src

builder.go (94823B)

---

 // Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package ssa
 
 // This file defines the builder, which builds SSA-form IR for function bodies.
 //
 // SSA construction has two phases, "create" and "build". First, one
 // or more packages are created in any order by a sequence of calls to
 // CreatePackage, either from syntax or from mere type information.
 // Each created package has a complete set of Members (const, var,
 // type, func) that can be accessed through methods like
 // Program.FuncValue.
 //
 // It is not necessary to call CreatePackage for all dependencies of
 // each syntax package, only for its direct imports. (In future
 // perhaps even this restriction may be lifted.)
 //
 // Second, packages created from syntax are built, by one or more
 // calls to Package.Build, which may be concurrent; or by a call to
 // Program.Build, which builds all packages in parallel. Building
 // traverses the type-annotated syntax tree of each function body and
 // creates SSA-form IR, a control-flow graph of instructions,
 // populating fields such as Function.Body, .Params, and others.
 //
 // Building may create additional methods, including:
 // - wrapper methods (e.g. for embedding, or implicit &recv)
 // - bound method closures (e.g. for use(recv.f))
 // - thunks (e.g. for use(I.f) or use(T.f))
 // - generic instances (e.g. to produce f[int] from f[any]).
 // As these methods are created, they are added to the build queue,
 // and then processed in turn, until a fixed point is reached,
 // Since these methods might belong to packages that were not
 // created (by a call to CreatePackage), their Pkg field is unset.
 //
 // Instances of generic functions may be either instantiated (f[int]
 // is a copy of f[T] with substitutions) or wrapped (f[int] delegates
 // to f[T]), depending on the availability of generic syntax and the
 // InstantiateGenerics mode flag.
 //
 // Each package has an initializer function named "init" that calls
 // the initializer functions of each direct import, computes and
 // assigns the initial value of each global variable, and calls each
 // source-level function named "init". (These generate SSA functions
 // named "init#1", "init#2", etc.)
 //
 // Runtime types
 //
 // Each MakeInterface operation is a conversion from a non-interface
 // type to an interface type. The semantics of this operation requires
 // a runtime type descriptor, which is the type portion of an
 // interface, and the value abstracted by reflect.Type.
 //
 // The program accumulates all non-parameterized types that are
 // encountered as MakeInterface operands, along with all types that
 // may be derived from them using reflection. This set is available as
 // Program.RuntimeTypes, and the methods of these types may be
 // reachable via interface calls or reflection even if they are never
 // referenced from the SSA IR. (In practice, algorithms such as RTA
 // that compute reachability from package main perform their own
 // tracking of runtime types at a finer grain, so this feature is not
 // very useful.)
 //
 // Function literals
 //
 // Anonymous functions must be built as soon as they are encountered,
 // as it may affect locals of the enclosing function, but they are not
 // marked 'built' until the end of the outermost enclosing function.
 // (Among other things, this causes them to be logged in top-down order.)
 //
 // The Function.build fields determines the algorithm for building the
 // function body. It is cleared to mark that building is complete.
 
 import (
 	"fmt"
 	"go/ast"
 	"go/constant"
 	"go/token"
 	"go/types"
 	"os"
 	"runtime"
 	"sync"
 
 	"slices"
 
 	"golang.org/x/tools/internal/typeparams"
 	"golang.org/x/tools/internal/typesinternal"
 	"golang.org/x/tools/internal/versions"
 )
 
 type opaqueType struct{ name string }
 
 func (t *opaqueType) String() string         { return t.name }
 func (t *opaqueType) Underlying() types.Type { return t }
 
 var (
 	varOk    = newVar("ok", tBool)
 	varIndex = newVar("index", tInt)
 
 	// Type constants.
 	tBool       = types.Typ[types.Bool]
 	tByte       = types.Typ[types.Byte]
 	tRune       = types.Universe.Lookup("rune").Type() // prints as "rune" (Typ[Rune] is same as Int32)
 	tInt        = types.Typ[types.Int]
 	tInvalid    = types.Typ[types.Invalid]
 	tString     = types.Typ[types.String]
 	tUntypedNil = types.Typ[types.UntypedNil]
 
 	tRangeIter  = &opaqueType{"iter"}                         // the type of all "range" iterators
 	tDeferStack = types.NewPointer(&opaqueType{"deferStack"}) // the type of a "deferStack" from ssa:deferstack()
 	tEface      = types.NewInterfaceType(nil, nil).Complete()
 
 	// SSA Value constants.
 	vZero     = intConst(0)
 	vOne      = intConst(1)
 	vTrue     = NewConst(constant.MakeBool(true), tBool)
 	vFalse    = NewConst(constant.MakeBool(false), tBool)
 	vNoReturn = NewConst(constant.MakeString("noreturn"), tString)
 
 	jReady = intConst(0)  // range-over-func jump is READY
 	jBusy  = intConst(-1) // range-over-func jump is BUSY
 	jDone  = intConst(-2) // range-over-func jump is DONE
 
 	// The ssa:deferstack intrinsic returns the current function's defer stack.
 	vDeferStack = &Builtin{
 		name: "ssa:deferstack",
 		sig:  types.NewSignatureType(nil, nil, nil, nil, typesinternal.TupleOf(tDeferStack), false),
 	}
 )
 
 // builder holds state associated with the package currently being built.
 // Its methods contain all the logic for AST-to-SSA conversion.
 //
 // All Functions belong to the same Program.
 //
 // builders are not thread-safe.
 type builder struct {
 	fns []*Function // Functions that have finished their CREATE phases.
 
 	finished int // finished is the length of the prefix of fns containing built functions.
 
 	// The task of building shared functions within the builder.
 	// Shared functions are ones the builder may either create or lookup.
 	// These may be built by other builders in parallel.
 	// The task is done when the builder has finished iterating, and it
 	// waits for all shared functions to finish building.
 	// nil implies there are no hared functions to wait on.
 	buildshared *task
 }
 
 // shared is done when the builder has built all of the
 // enqueued functions to a fixed-point.
 func (b *builder) shared() *task {
 	if b.buildshared == nil { // lazily-initialize
 		b.buildshared = &task{done: make(chan unit)}
 	}
 	return b.buildshared
 }
 
 // enqueue fn to be built by the builder.
 func (b *builder) enqueue(fn *Function) {
 	b.fns = append(b.fns, fn)
 }
 
 // waitForSharedFunction indicates that the builder should wait until
 // the potentially shared function fn has finished building.
 //
 // This should include any functions that may be built by other
 // builders.
 func (b *builder) waitForSharedFunction(fn *Function) {
 	if fn.buildshared != nil { // maybe need to wait?
 		s := b.shared()
 		s.addEdge(fn.buildshared)
 	}
 }
 
 // cond emits to fn code to evaluate boolean condition e and jump
 // to t or f depending on its value, performing various simplifications.
 //
 // Postcondition: fn.currentBlock is nil.
 func (b *builder) cond(fn *Function, e ast.Expr, t, f *BasicBlock) {
 	switch e := e.(type) {
 	case *ast.ParenExpr:
 		b.cond(fn, e.X, t, f)
 		return
 
 	case *ast.BinaryExpr:
 		switch e.Op {
 		case token.LAND:
 			ltrue := fn.newBasicBlock("cond.true")
 			b.cond(fn, e.X, ltrue, f)
 			fn.currentBlock = ltrue
 			b.cond(fn, e.Y, t, f)
 			return
 
 		case token.LOR:
 			lfalse := fn.newBasicBlock("cond.false")
 			b.cond(fn, e.X, t, lfalse)
 			fn.currentBlock = lfalse
 			b.cond(fn, e.Y, t, f)
 			return
 		}
 
 	case *ast.UnaryExpr:
 		if e.Op == token.NOT {
 			b.cond(fn, e.X, f, t)
 			return
 		}
 	}
 
 	// A traditional compiler would simplify "if false" (etc) here
 	// but we do not, for better fidelity to the source code.
 	//
 	// The value of a constant condition may be platform-specific,
 	// and may cause blocks that are reachable in some configuration
 	// to be hidden from subsequent analyses such as bug-finding tools.
 	emitIf(fn, b.expr(fn, e), t, f)
 }
 
 // logicalBinop emits code to fn to evaluate e, a &&- or
 // ||-expression whose reified boolean value is wanted.
 // The value is returned.
 func (b *builder) logicalBinop(fn *Function, e *ast.BinaryExpr) Value {
 	rhs := fn.newBasicBlock("binop.rhs")
 	done := fn.newBasicBlock("binop.done")
 
 	// T(e) = T(e.X) = T(e.Y) after untyped constants have been
 	// eliminated.
 	// TODO(adonovan): not true; MyBool==MyBool yields UntypedBool.
 	t := fn.typeOf(e)
 
 	var short Value // value of the short-circuit path
 	switch e.Op {
 	case token.LAND:
 		b.cond(fn, e.X, rhs, done)
 		short = NewConst(constant.MakeBool(false), t)
 
 	case token.LOR:
 		b.cond(fn, e.X, done, rhs)
 		short = NewConst(constant.MakeBool(true), t)
 	}
 
 	// Is rhs unreachable?
 	if rhs.Preds == nil {
 		// Simplify false&&y to false, true||y to true.
 		fn.currentBlock = done
 		return short
 	}
 
 	// Is done unreachable?
 	if done.Preds == nil {
 		// Simplify true&&y (or false||y) to y.
 		fn.currentBlock = rhs
 		return b.expr(fn, e.Y)
 	}
 
 	// All edges from e.X to done carry the short-circuit value.
 	var edges []Value
 	for range done.Preds {
 		edges = append(edges, short)
 	}
 
 	// The edge from e.Y to done carries the value of e.Y.
 	fn.currentBlock = rhs
 	edges = append(edges, b.expr(fn, e.Y))
 	emitJump(fn, done)
 	fn.currentBlock = done
 
 	phi := &Phi{Edges: edges, Comment: e.Op.String()}
 	phi.pos = e.OpPos
 	phi.typ = t
 	return done.emit(phi)
 }
 
 // exprN lowers a multi-result expression e to SSA form, emitting code
 // to fn and returning a single Value whose type is a *types.Tuple.
 // The caller must access the components via Extract.
 //
 // Multi-result expressions include CallExprs in a multi-value
 // assignment or return statement, and "value,ok" uses of
 // TypeAssertExpr, IndexExpr (when X is a map), and UnaryExpr (when Op
 // is token.ARROW).
 func (b *builder) exprN(fn *Function, e ast.Expr) Value {
 	typ := fn.typeOf(e).(*types.Tuple)
 	switch e := e.(type) {
 	case *ast.ParenExpr:
 		return b.exprN(fn, e.X)
 
 	case *ast.CallExpr:
 		// Currently, no built-in function nor type conversion
 		// has multiple results, so we can avoid some of the
 		// cases for single-valued CallExpr.
 		var c Call
 		b.setCall(fn, e, &c.Call)
 		c.typ = typ
 		return emitCall(fn, &c)
 
 	case *ast.IndexExpr:
 		mapt := typeparams.CoreType(fn.typeOf(e.X)).(*types.Map) // ,ok must be a map.
 		lookup := &Lookup{
 			X:       b.expr(fn, e.X),
 			Index:   emitConv(fn, b.expr(fn, e.Index), mapt.Key()),
 			CommaOk: true,
 		}
 		lookup.setType(typ)
 		lookup.setPos(e.Lbrack)
 		return fn.emit(lookup)
 
 	case *ast.TypeAssertExpr:
 		return emitTypeTest(fn, b.expr(fn, e.X), typ.At(0).Type(), e.Lparen)
 
 	case *ast.UnaryExpr: // must be receive <-
 		unop := &UnOp{
 			Op:      token.ARROW,
 			X:       b.expr(fn, e.X),
 			CommaOk: true,
 		}
 		unop.setType(typ)
 		unop.setPos(e.OpPos)
 		return fn.emit(unop)
 	}
 	panic(fmt.Sprintf("exprN(%T) in %s", e, fn))
 }
 
 // builtin emits to fn SSA instructions to implement a call to the
 // built-in function obj with the specified arguments
 // and return type.  It returns the value defined by the result.
 //
 // The result is nil if no special handling was required; in this case
 // the caller should treat this like an ordinary library function
 // call.
 func (b *builder) builtin(fn *Function, obj *types.Builtin, args []ast.Expr, typ types.Type, pos token.Pos) Value {
 	typ = fn.typ(typ)
 	switch obj.Name() {
 	case "make":
 		switch ct := typeparams.CoreType(typ).(type) {
 		case *types.Slice:
 			n := b.expr(fn, args[1])
 			m := n
 			if len(args) == 3 {
 				m = b.expr(fn, args[2])
 			}
 			if m, ok := m.(*Const); ok {
 				// treat make([]T, n, m) as new([m]T)[:n]
 				cap := m.Int64()
 				at := types.NewArray(ct.Elem(), cap)
 				v := &Slice{
 					X:    emitNew(fn, at, pos, "makeslice"),
 					High: n,
 				}
 				v.setPos(pos)
 				v.setType(typ)
 				return fn.emit(v)
 			}
 			v := &MakeSlice{
 				Len: n,
 				Cap: m,
 			}
 			v.setPos(pos)
 			v.setType(typ)
 			return fn.emit(v)
 
 		case *types.Map:
 			var res Value
 			if len(args) == 2 {
 				res = b.expr(fn, args[1])
 			}
 			v := &MakeMap{Reserve: res}
 			v.setPos(pos)
 			v.setType(typ)
 			return fn.emit(v)
 
 		case *types.Chan:
 			var sz Value = vZero
 			if len(args) == 2 {
 				sz = b.expr(fn, args[1])
 			}
 			v := &MakeChan{Size: sz}
 			v.setPos(pos)
 			v.setType(typ)
 			return fn.emit(v)
 		}
 
 	case "new":
 		alloc := emitNew(fn, typeparams.MustDeref(typ), pos, "new")
 		if !fn.info.Types[args[0]].IsType() {
 			// new(expr), requires go1.26
 			v := b.expr(fn, args[0])
 			emitStore(fn, alloc, v, pos)
 		}
 		return alloc
 
 	case "len", "cap":
 		// Special case: len or cap of an array or *array is
 		// based on the type, not the value which may be nil.
 		// We must still evaluate the value, though.  (If it
 		// was side-effect free, the whole call would have
 		// been constant-folded.)
 		t := typeparams.Deref(fn.typeOf(args[0]))
 		if at, ok := typeparams.CoreType(t).(*types.Array); ok {
 			b.expr(fn, args[0]) // for effects only
 			return intConst(at.Len())
 		}
 		// Otherwise treat as normal.
 
 	case "panic":
 		fn.emit(&Panic{
 			X:   emitConv(fn, b.expr(fn, args[0]), tEface),
 			pos: pos,
 		})
 		fn.currentBlock = fn.newBasicBlock("unreachable")
 		return vTrue // any non-nil Value will do
 	}
 	return nil // treat all others as a regular function call
 }
 
 // addr lowers a single-result addressable expression e to SSA form,
 // emitting code to fn and returning the location (an lvalue) defined
 // by the expression.
 //
 // If escaping is true, addr marks the base variable of the
 // addressable expression e as being a potentially escaping pointer
 // value.  For example, in this code:
 //
 //	a := A{
 //	  b: [1]B{B{c: 1}}
 //	}
 //	return &a.b[0].c
 //
 // the application of & causes a.b[0].c to have its address taken,
 // which means that ultimately the local variable a must be
 // heap-allocated.  This is a simple but very conservative escape
 // analysis.
 //
 // Operations forming potentially escaping pointers include:
 // - &x, including when implicit in method call or composite literals.
 // - a[:] iff a is an array (not *array)
 // - references to variables in lexically enclosing functions.
 func (b *builder) addr(fn *Function, e ast.Expr, escaping bool) lvalue {
 	switch e := e.(type) {
 	case *ast.Ident:
 		if isBlankIdent(e) {
 			return blank{}
 		}
 		obj := fn.objectOf(e).(*types.Var)
 		var v Value
 		if g := fn.Prog.packageLevelMember(obj); g != nil {
 			v = g.(*Global) // var (address)
 		} else {
 			v = fn.lookup(obj, escaping)
 		}
 		return &address{addr: v, pos: e.Pos(), expr: e}
 
 	case *ast.CompositeLit:
 		typ := typeparams.Deref(fn.typeOf(e))
 		var v *Alloc
 		if escaping {
 			v = emitNew(fn, typ, e.Lbrace, "complit")
 		} else {
 			v = emitLocal(fn, typ, e.Lbrace, "complit")
 		}
 		var sb storebuf
 		b.compLit(fn, v, e, true, &sb)
 		sb.emit(fn)
 		return &address{addr: v, pos: e.Lbrace, expr: e}
 
 	case *ast.ParenExpr:
 		return b.addr(fn, e.X, escaping)
 
 	case *ast.SelectorExpr:
 		sel := fn.selection(e)
 		if sel == nil {
 			// qualified identifier
 			return b.addr(fn, e.Sel, escaping)
 		}
 		if sel.kind != types.FieldVal {
 			panic(sel)
 		}
 		wantAddr := true
 		v := b.receiver(fn, e.X, wantAddr, escaping, sel)
 		index := sel.index[len(sel.index)-1]
 		fld := fieldOf(typeparams.MustDeref(v.Type()), index) // v is an addr.
 
 		// Due to the two phases of resolving AssignStmt, a panic from x.f = p()
 		// when x is nil is required to come after the side-effects of
 		// evaluating x and p().
 		emit := func(fn *Function) Value {
 			return emitFieldSelection(fn, v, index, true, e.Sel)
 		}
 		return &lazyAddress{addr: emit, t: fld.Type(), pos: e.Sel.Pos(), expr: e.Sel}
 
 	case *ast.IndexExpr:
 		xt := fn.typeOf(e.X)
 		elem, mode := indexType(xt)
 		var x Value
 		var et types.Type
 		switch mode {
 		case ixArrVar: // array, array|slice, array|*array, or array|*array|slice.
 			x = b.addr(fn, e.X, escaping).address(fn)
 			et = types.NewPointer(elem)
 		case ixVar: // *array, slice, *array|slice
 			x = b.expr(fn, e.X)
 			et = types.NewPointer(elem)
 		case ixMap:
 			mt := typeparams.CoreType(xt).(*types.Map)
 			return &element{
 				m:   b.expr(fn, e.X),
 				k:   emitConv(fn, b.expr(fn, e.Index), mt.Key()),
 				t:   mt.Elem(),
 				pos: e.Lbrack,
 			}
 		default:
 			panic("unexpected container type in IndexExpr: " + xt.String())
 		}
 		index := b.expr(fn, e.Index)
 		if isUntyped(index.Type()) {
 			index = emitConv(fn, index, tInt)
 		}
 		// Due to the two phases of resolving AssignStmt, a panic from x[i] = p()
 		// when x is nil or i is out-of-bounds is required to come after the
 		// side-effects of evaluating x, i and p().
 		emit := func(fn *Function) Value {
 			v := &IndexAddr{
 				X:     x,
 				Index: index,
 			}
 			v.setPos(e.Lbrack)
 			v.setType(et)
 			return fn.emit(v)
 		}
 		return &lazyAddress{addr: emit, t: typeparams.MustDeref(et), pos: e.Lbrack, expr: e}
 
 	case *ast.StarExpr:
 		return &address{addr: b.expr(fn, e.X), pos: e.Star, expr: e}
 	}
 
 	panic(fmt.Sprintf("unexpected address expression: %T", e))
 }
 
 type store struct {
 	lhs lvalue
 	rhs Value
 }
 
 type storebuf struct{ stores []store }
 
 func (sb *storebuf) store(lhs lvalue, rhs Value) {
 	sb.stores = append(sb.stores, store{lhs, rhs})
 }
 
 func (sb *storebuf) emit(fn *Function) {
 	for _, s := range sb.stores {
 		s.lhs.store(fn, s.rhs)
 	}
 }
 
 // assign emits to fn code to initialize the lvalue loc with the value
 // of expression e.  If isZero is true, assign assumes that loc holds
 // the zero value for its type.
 //
 // This is equivalent to loc.store(fn, b.expr(fn, e)), but may generate
 // better code in some cases, e.g., for composite literals in an
 // addressable location.
 //
 // If sb is not nil, assign generates code to evaluate expression e, but
 // not to update loc.  Instead, the necessary stores are appended to the
 // storebuf sb so that they can be executed later.  This allows correct
 // in-place update of existing variables when the RHS is a composite
 // literal that may reference parts of the LHS.
 func (b *builder) assign(fn *Function, loc lvalue, e ast.Expr, isZero bool, sb *storebuf) {
 	// Can we initialize it in place?
 	if e, ok := ast.Unparen(e).(*ast.CompositeLit); ok {
 		// A CompositeLit never evaluates to a pointer,
 		// so if the type of the location is a pointer,
 		// an &-operation is implied.
 		if !is[blank](loc) && isPointerCore(loc.typ()) { // avoid calling blank.typ()
 			ptr := b.addr(fn, e, true).address(fn)
 			// copy address
 			if sb != nil {
 				sb.store(loc, ptr)
 			} else {
 				loc.store(fn, ptr)
 			}
 			return
 		}
 	}
 
 	// simple case: just copy
 	rhs := b.expr(fn, e)
 	if sb != nil {
 		sb.store(loc, rhs)
 	} else {
 		loc.store(fn, rhs)
 	}
 }
 
 // expr lowers a single-result expression e to SSA form, emitting code
 // to fn and returning the Value defined by the expression.
 func (b *builder) expr(fn *Function, e ast.Expr) Value {
 	e = ast.Unparen(e)
 
 	tv := fn.info.Types[e]
 
 	// Is expression a constant?
 	if tv.Value != nil {
 		return NewConst(tv.Value, fn.typ(tv.Type))
 	}
 
 	var v Value
 	if tv.Addressable() {
 		// Prefer pointer arithmetic ({Index,Field}Addr) followed
 		// by Load over subelement extraction (e.g. Index, Field),
 		// to avoid large copies.
 		v = b.addr(fn, e, false).load(fn)
 	} else {
 		v = b.expr0(fn, e, tv)
 	}
 	if fn.debugInfo() {
 		emitDebugRef(fn, e, v, false)
 	}
 	return v
 }
 
 func (b *builder) expr0(fn *Function, e ast.Expr, tv types.TypeAndValue) Value {
 	switch e := e.(type) {
 	case *ast.BasicLit:
 		panic("non-constant BasicLit") // unreachable
 
 	case *ast.FuncLit:
 		/* function literal */
 		anon := &Function{
 			name:           fmt.Sprintf("%s$%d", fn.Name(), 1+len(fn.AnonFuncs)),
 			Signature:      fn.typeOf(e.Type).(*types.Signature),
 			pos:            e.Type.Func,
 			parent:         fn,
 			anonIdx:        int32(len(fn.AnonFuncs)),
 			Pkg:            fn.Pkg,
 			Prog:           fn.Prog,
 			syntax:         e,
 			info:           fn.info,
 			goversion:      fn.goversion,
 			build:          (*builder).buildFromSyntax,
 			topLevelOrigin: nil,           // use anonIdx to lookup an anon instance's origin.
 			typeparams:     fn.typeparams, // share the parent's type parameters.
 			typeargs:       fn.typeargs,   // share the parent's type arguments.
 			subst:          fn.subst,      // share the parent's type substitutions.
 			uniq:           fn.uniq,       // start from parent's unique values
 		}
 		fn.AnonFuncs = append(fn.AnonFuncs, anon)
 		// Build anon immediately, as it may cause fn's locals to escape.
 		// (It is not marked 'built' until the end of the enclosing FuncDecl.)
 		anon.build(b, anon)
 		fn.uniq = anon.uniq // resume after anon's unique values
 		if anon.FreeVars == nil {
 			return anon
 		}
 		v := &MakeClosure{Fn: anon}
 		v.setType(fn.typ(tv.Type))
 		for _, fv := range anon.FreeVars {
 			v.Bindings = append(v.Bindings, fv.outer)
 			fv.outer = nil
 		}
 		return fn.emit(v)
 
 	case *ast.TypeAssertExpr: // single-result form only
 		return emitTypeAssert(fn, b.expr(fn, e.X), fn.typ(tv.Type), e.Lparen)
 
 	case *ast.CallExpr:
 		if fn.info.Types[e.Fun].IsType() {
 			// Explicit type conversion, e.g. string(x) or big.Int(x)
 			x := b.expr(fn, e.Args[0])
 			y := emitConv(fn, x, fn.typ(tv.Type))
 			if y != x {
 				switch y := y.(type) {
 				case *Convert:
 					y.pos = e.Lparen
 				case *ChangeType:
 					y.pos = e.Lparen
 				case *MakeInterface:
 					y.pos = e.Lparen
 				case *SliceToArrayPointer:
 					y.pos = e.Lparen
 				case *UnOp: // conversion from slice to array.
 					y.pos = e.Lparen
 				}
 			}
 			return y
 		}
 		// Call to "intrinsic" built-ins, e.g. new, make, panic.
 		if id, ok := ast.Unparen(e.Fun).(*ast.Ident); ok {
 			if obj, ok := fn.info.Uses[id].(*types.Builtin); ok {
 				if v := b.builtin(fn, obj, e.Args, fn.typ(tv.Type), e.Lparen); v != nil {
 					return v
 				}
 			}
 		}
 		// Regular function call.
 		var v Call
 		b.setCall(fn, e, &v.Call)
 		v.setType(fn.typ(tv.Type))
 		return emitCall(fn, &v)
 
 	case *ast.UnaryExpr:
 		switch e.Op {
 		case token.AND: // &X --- potentially escaping.
 			addr := b.addr(fn, e.X, true)
 			if _, ok := ast.Unparen(e.X).(*ast.StarExpr); ok {
 				// &*p must panic if p is nil (http://golang.org/s/go12nil).
 				// For simplicity, we'll just (suboptimally) rely
 				// on the side effects of a load.
 				// TODO(adonovan): emit dedicated nilcheck.
 				addr.load(fn)
 			}
 			return addr.address(fn)
 		case token.ADD:
 			return b.expr(fn, e.X)
 		case token.NOT, token.ARROW, token.SUB, token.XOR: // ! <- - ^
 			v := &UnOp{
 				Op: e.Op,
 				X:  b.expr(fn, e.X),
 			}
 			v.setPos(e.OpPos)
 			v.setType(fn.typ(tv.Type))
 			return fn.emit(v)
 		default:
 			panic(e.Op)
 		}
 
 	case *ast.BinaryExpr:
 		switch e.Op {
 		case token.LAND, token.LOR:
 			return b.logicalBinop(fn, e)
 		case token.SHL, token.SHR:
 			fallthrough
 		case token.ADD, token.SUB, token.MUL, token.QUO, token.REM, token.AND, token.OR, token.XOR, token.AND_NOT:
 			return emitArith(fn, e.Op, b.expr(fn, e.X), b.expr(fn, e.Y), fn.typ(tv.Type), e.OpPos)
 
 		case token.EQL, token.NEQ, token.GTR, token.LSS, token.LEQ, token.GEQ:
 			cmp := emitCompare(fn, e.Op, b.expr(fn, e.X), b.expr(fn, e.Y), e.OpPos)
 			// The type of x==y may be UntypedBool.
 			return emitConv(fn, cmp, types.Default(fn.typ(tv.Type)))
 		default:
 			panic("illegal op in BinaryExpr: " + e.Op.String())
 		}
 
 	case *ast.SliceExpr:
 		var low, high, max Value
 		var x Value
 		xtyp := fn.typeOf(e.X)
 		switch typeparams.CoreType(xtyp).(type) {
 		case *types.Array:
 			// Potentially escaping.
 			x = b.addr(fn, e.X, true).address(fn)
 		case *types.Basic, *types.Slice, *types.Pointer: // *array
 			x = b.expr(fn, e.X)
 		default:
 			// core type exception?
 			if isBytestring(xtyp) {
 				x = b.expr(fn, e.X) // bytestring is handled as string and []byte.
 			} else {
 				panic("unexpected sequence type in SliceExpr")
 			}
 		}
 		if e.Low != nil {
 			low = b.expr(fn, e.Low)
 		}
 		if e.High != nil {
 			high = b.expr(fn, e.High)
 		}
 		if e.Slice3 {
 			max = b.expr(fn, e.Max)
 		}
 		v := &Slice{
 			X:    x,
 			Low:  low,
 			High: high,
 			Max:  max,
 		}
 		v.setPos(e.Lbrack)
 		v.setType(fn.typ(tv.Type))
 		return fn.emit(v)
 
 	case *ast.Ident:
 		obj := fn.info.Uses[e]
 		// Universal built-in or nil?
 		switch obj := obj.(type) {
 		case *types.Builtin:
 			return &Builtin{name: obj.Name(), sig: fn.instanceType(e).(*types.Signature)}
 		case *types.Nil:
 			return zeroConst(fn.instanceType(e))
 		}
 
 		// Package-level func or var?
 		// (obj must belong to same package or a direct import.)
 		if v := fn.Prog.packageLevelMember(obj); v != nil {
 			if g, ok := v.(*Global); ok {
 				return emitLoad(fn, g) // var (address)
 			}
 			callee := v.(*Function) // (func)
 			if callee.typeparams.Len() > 0 {
 				targs := fn.subtargs(e)
 				callee = callee.instance(nil, targs, b)
 			}
 			return callee
 		}
 		// Local var.
 		return emitLoad(fn, fn.lookup(obj.(*types.Var), false)) // var (address)
 
 	case *ast.SelectorExpr:
 		sel := fn.selection(e)
 		if sel == nil {
 			// builtin unsafe.{Add,Slice}
 			if obj, ok := fn.info.Uses[e.Sel].(*types.Builtin); ok {
 				return &Builtin{name: obj.Name(), sig: fn.typ(tv.Type).(*types.Signature)}
 			}
 			// qualified identifier
 			return b.expr(fn, e.Sel)
 		}
 		switch sel.kind {
 		case types.MethodExpr:
 			// (*T).f or T.f, the method f from the method-set of type T.
 			// The result is a "thunk".
 			targs := fn.subtargs(e.Sel)
 			thunk := createThunk(fn.Prog, sel, targs)
 			b.enqueue(thunk)
 			return thunk
 
 		case types.MethodVal:
 			// e.f where e is an expression and f is a method.
 			// The result is a "bound".
 			m := sel.obj.(*types.Func)
 			rt := fn.typ(recvType(m))
 			wantAddr := isPointer(rt)
 			escaping := true
 			v := b.receiver(fn, e.X, wantAddr, escaping, sel)
 
 			if types.IsInterface(rt) {
 				// If v may be an interface type I (after instantiating),
 				// we must emit a check that v is non-nil.
 				if recv, ok := types.Unalias(sel.recv).(*types.TypeParam); ok {
 					// Emit a nil check if any possible instantiation of the
 					// type parameter is an interface type.
 					if !typeSetIsEmpty(recv) {
 						// recv has a concrete term its typeset.
 						// So it cannot be instantiated as an interface.
 						//
 						// Example:
 						// func _[T interface{~int; Foo()}] () {
 						//    var v T
 						//    _ = v.Foo // <-- MethodVal
 						// }
 					} else {
 						// rt may be instantiated as an interface.
 						// Emit nil check: typeassert (any(v)).(any).
 						emitTypeAssert(fn, emitConv(fn, v, tEface), tEface, token.NoPos)
 					}
 				} else {
 					// non-type param interface
 					// Emit nil check: typeassert v.(I).
 					emitTypeAssert(fn, v, rt, e.Sel.Pos())
 				}
 			}
 
 			if rtargs := fn.subrtargs(m); len(rtargs) > 0 {
 				m = fn.Prog.canon.instantiateMethod(m, rtargs, fn.Prog.ctxt)
 			}
 
 			targs := fn.subtargs(e.Sel)
 			bound := createBound(fn.Prog, m, targs)
 			b.enqueue(bound)
 
 			// The assignment may widen a type parameter to its
 			// interface bound (case #3 of go.dev/issue.78110).
 			v = emitConv(fn, v, bound.FreeVars[0].Type())
 
 			c := &MakeClosure{
 				Fn:       bound,
 				Bindings: []Value{v},
 			}
 			c.setPos(e.Sel.Pos())
 			c.setType(bound.Signature)
 			return fn.emit(c)
 
 		case types.FieldVal:
 			indices := sel.index
 			last := len(indices) - 1
 			v := b.expr(fn, e.X)
 			v = emitImplicitSelections(fn, v, indices[:last], e.Pos())
 			v = emitFieldSelection(fn, v, indices[last], false, e.Sel)
 			return v
 		}
 
 		panic("unexpected expression-relative selector")
 
 	case *ast.IndexListExpr:
 		// f[X, Y] must be a generic function
 		if !instance(fn.info, e.X) {
 			panic("unexpected expression-could not match index list to instantiation")
 		}
 		return b.expr(fn, e.X) // Handle instantiation within the *Ident or *SelectorExpr cases.
 
 	case *ast.IndexExpr:
 		if instance(fn.info, e.X) {
 			return b.expr(fn, e.X) // Handle instantiation within the *Ident or *SelectorExpr cases.
 		}
 		// not a generic instantiation.
 		xt := fn.typeOf(e.X)
 		switch et, mode := indexType(xt); mode {
 		case ixVar:
 			// Addressable slice/array; use IndexAddr and Load.
 			return b.addr(fn, e, false).load(fn)
 
 		case ixArrVar, ixValue:
 			// An array in a register, a string or a combined type that contains
 			// either an [_]array (ixArrVar) or string (ixValue).
 
 			// Note: for ixArrVar and CoreType(xt)==nil can be IndexAddr and Load.
 			index := b.expr(fn, e.Index)
 			if isUntyped(index.Type()) {
 				index = emitConv(fn, index, tInt)
 			}
 			v := &Index{
 				X:     b.expr(fn, e.X),
 				Index: index,
 			}
 			v.setPos(e.Lbrack)
 			v.setType(et)
 			return fn.emit(v)
 
 		case ixMap:
 			ct := typeparams.CoreType(xt).(*types.Map)
 			v := &Lookup{
 				X:     b.expr(fn, e.X),
 				Index: emitConv(fn, b.expr(fn, e.Index), ct.Key()),
 			}
 			v.setPos(e.Lbrack)
 			v.setType(ct.Elem())
 			return fn.emit(v)
 		default:
 			panic("unexpected container type in IndexExpr: " + xt.String())
 		}
 
 	case *ast.CompositeLit, *ast.StarExpr:
 		// Addressable types (lvalues)
 		return b.addr(fn, e, false).load(fn)
 	}
 
 	panic(fmt.Sprintf("unexpected expr: %T", e))
 }
 
 // stmtList emits to fn code for all statements in list.
 func (b *builder) stmtList(fn *Function, list []ast.Stmt) {
 	for _, s := range list {
 		b.stmt(fn, s)
 	}
 }
 
 // receiver emits to fn code for expression e in the "receiver"
 // position of selection e.f (where f may be a field or a method) and
 // returns the effective receiver after applying the implicit field
 // selections of sel.
 //
 // wantAddr requests that the result is an address.  If
 // !sel.indirect, this may require that e be built in addr() mode; it
 // must thus be addressable.
 //
 // escaping is defined as per builder.addr().
 func (b *builder) receiver(fn *Function, e ast.Expr, wantAddr, escaping bool, sel *selection) Value {
 	var v Value
 	if wantAddr && !sel.indirect && !isPointerCore(fn.typeOf(e)) {
 		v = b.addr(fn, e, escaping).address(fn)
 	} else {
 		v = b.expr(fn, e)
 	}
 
 	last := len(sel.index) - 1
 	// The position of implicit selection is the position of the inducing receiver expression.
 	v = emitImplicitSelections(fn, v, sel.index[:last], e.Pos())
 	if types.IsInterface(v.Type()) {
 		// When v is an interface, sel.Kind()==MethodValue and v.f is invoked.
 		// So v is not loaded, even if v has a pointer core type.
 	} else if !wantAddr && isPointerCore(v.Type()) {
 		v = emitLoad(fn, v)
 	}
 	return v
 }
 
 // setCallFunc populates the function parts of a CallCommon structure
 // (Func, Method, Recv, Args[0]) based on the kind of invocation
 // occurring in e.
 func (b *builder) setCallFunc(fn *Function, e *ast.CallExpr, c *CallCommon) {
 	c.pos = e.Lparen
 
 	// Is this a (possibly generic) method call?
 	m := ast.Unparen(e.Fun)
 	switch e := m.(type) {
 	case *ast.IndexExpr:
 		m = e.X
 	case *ast.IndexListExpr:
 		m = e.X
 	}
 	if selector, ok := m.(*ast.SelectorExpr); ok {
 		sel := fn.selection(selector)
 		if sel != nil && sel.kind == types.MethodVal {
 			obj := sel.obj.(*types.Func)
 			recv := recvType(obj)
 
 			wantAddr := isPointer(recv)
 			escaping := true
 			v := b.receiver(fn, selector.X, wantAddr, escaping, sel)
 			if types.IsInterface(recv) {
 				// Invoke-mode call.
 				c.Value = v // possibly type param
 				c.Method = obj
 			} else {
 				// "Call"-mode call.
 				targs := fn.subtargs(selector.Sel)
 				c.Value = fn.Prog.objectMethod(obj, targs, b)
 				c.Args = append(c.Args, v)
 			}
 			return
 		}
 
 		// sel.kind==MethodExpr indicates T.f() or (*T).f():
 		// a statically dispatched call to the method f in the
 		// method-set of T or *T.  T may be an interface.
 		//
 		// e.Fun would evaluate to a concrete method, interface
 		// wrapper function, or promotion wrapper.
 		//
 		// For now, we evaluate it in the usual way.
 		//
 		// TODO(adonovan): opt: inline expr() here, to make the
 		// call static and to avoid generation of wrappers.
 		// It's somewhat tricky as it may consume the first
 		// actual parameter if the call is "invoke" mode.
 		//
 		// Examples:
 		//  type T struct{}; func (T) f() {}   // "call" mode
 		//  type T interface { f() }           // "invoke" mode
 		//
 		//  type S struct{ T }
 		//
 		//  var s S
 		//  S.f(s)
 		//  (*S).f(&s)
 		//
 		// Suggested approach:
 		// - consume the first actual parameter expression
 		//   and build it with b.expr().
 		// - apply implicit field selections.
 		// - use MethodVal logic to populate fields of c.
 	}
 
 	// Evaluate the function operand in the usual way.
 	c.Value = b.expr(fn, e.Fun)
 }
 
 // emitCallArgs emits to f code for the actual parameters of call e to
 // a (possibly built-in) function of effective type sig.
 // The argument values are appended to args, which is then returned.
 func (b *builder) emitCallArgs(fn *Function, sig *types.Signature, e *ast.CallExpr, args []Value) []Value {
 	// f(x, y, z...): pass slice z straight through.
 	if e.Ellipsis != 0 {
 		for i, arg := range e.Args {
 			v := emitConv(fn, b.expr(fn, arg), sig.Params().At(i).Type())
 			args = append(args, v)
 		}
 		return args
 	}
 
 	offset := len(args) // 1 if call has receiver, 0 otherwise
 
 	// Evaluate actual parameter expressions.
 	//
 	// If this is a chained call of the form f(g()) where g has
 	// multiple return values (MRV), they are flattened out into
 	// args; a suffix of them may end up in a varargs slice.
 	for _, arg := range e.Args {
 		v := b.expr(fn, arg)
 		if ttuple, ok := v.Type().(*types.Tuple); ok { // MRV chain
 			for i, n := 0, ttuple.Len(); i < n; i++ {
 				args = append(args, emitExtract(fn, v, i))
 			}
 		} else {
 			args = append(args, v)
 		}
 	}
 
 	// Actual->formal assignability conversions for normal parameters.
 	np := sig.Params().Len() // number of normal parameters
 	if sig.Variadic() {
 		np--
 	}
 	for i := 0; i < np; i++ {
 		args[offset+i] = emitConv(fn, args[offset+i], sig.Params().At(i).Type())
 	}
 
 	// Actual->formal assignability conversions for variadic parameter,
 	// and construction of slice.
 	if sig.Variadic() {
 		varargs := args[offset+np:]
 		st := sig.Params().At(np).Type().(*types.Slice)
 		vt := st.Elem()
 		if len(varargs) == 0 {
 			args = append(args, zeroConst(st))
 		} else {
 			// Replace a suffix of args with a slice containing it.
 			at := types.NewArray(vt, int64(len(varargs)))
 			a := emitNew(fn, at, token.NoPos, "varargs")
 			a.setPos(e.Rparen)
 			for i, arg := range varargs {
 				iaddr := &IndexAddr{
 					X:     a,
 					Index: intConst(int64(i)),
 				}
 				iaddr.setType(types.NewPointer(vt))
 				fn.emit(iaddr)
 				emitStore(fn, iaddr, arg, arg.Pos())
 			}
 			s := &Slice{X: a}
 			s.setType(st)
 			args[offset+np] = fn.emit(s)
 			args = args[:offset+np+1]
 		}
 	}
 	return args
 }
 
 // setCall emits to fn code to evaluate all the parameters of a function
 // call e, and populates *c with those values.
 func (b *builder) setCall(fn *Function, e *ast.CallExpr, c *CallCommon) {
 	// First deal with the f(...) part and optional receiver.
 	b.setCallFunc(fn, e, c)
 
 	// Then append the other actual parameters.
 	sig, _ := typeparams.CoreType(fn.typeOf(e.Fun)).(*types.Signature)
 	if sig == nil {
 		panic(fmt.Sprintf("no signature for call of %s", e.Fun))
 	}
 	c.Args = b.emitCallArgs(fn, sig, e, c.Args)
 }
 
 // assignOp emits to fn code to perform loc <op>= val.
 func (b *builder) assignOp(fn *Function, loc lvalue, val Value, op token.Token, pos token.Pos) {
 	loc.store(fn, emitArith(fn, op, loc.load(fn), val, loc.typ(), pos))
 }
 
 // localValueSpec emits to fn code to define all of the vars in the
 // function-local ValueSpec, spec.
 func (b *builder) localValueSpec(fn *Function, spec *ast.ValueSpec) {
 	switch {
 	case len(spec.Values) == len(spec.Names):
 		// e.g. var x, y = 0, 1
 		// 1:1 assignment
 		for i, id := range spec.Names {
 			if !isBlankIdent(id) {
 				emitLocalVar(fn, identVar(fn, id))
 			}
 			lval := b.addr(fn, id, false) // non-escaping
 			b.assign(fn, lval, spec.Values[i], true, nil)
 		}
 
 	case len(spec.Values) == 0:
 		// e.g. var x, y int
 		// Locals are implicitly zero-initialized.
 		for _, id := range spec.Names {
 			if !isBlankIdent(id) {
 				lhs := emitLocalVar(fn, identVar(fn, id))
 				if fn.debugInfo() {
 					emitDebugRef(fn, id, lhs, true)
 				}
 			}
 		}
 
 	default:
 		// e.g. var x, y = pos()
 		tuple := b.exprN(fn, spec.Values[0])
 		for i, id := range spec.Names {
 			if !isBlankIdent(id) {
 				emitLocalVar(fn, identVar(fn, id))
 				lhs := b.addr(fn, id, false) // non-escaping
 				lhs.store(fn, emitExtract(fn, tuple, i))
 			}
 		}
 	}
 }
 
 // assignStmt emits code to fn for a parallel assignment of rhss to lhss.
 // isDef is true if this is a short variable declaration (:=).
 //
 // Note the similarity with localValueSpec.
 func (b *builder) assignStmt(fn *Function, lhss, rhss []ast.Expr, isDef bool) {
 	// Side effects of all LHSs and RHSs must occur in left-to-right order.
 	lvals := make([]lvalue, len(lhss))
 	isZero := make([]bool, len(lhss))
 	for i, lhs := range lhss {
 		var lval lvalue = blank{}
 		if !isBlankIdent(lhs) {
 			if isDef {
 				if obj, ok := fn.info.Defs[lhs.(*ast.Ident)].(*types.Var); ok {
 					emitLocalVar(fn, obj)
 					isZero[i] = true
 				}
 			}
 			lval = b.addr(fn, lhs, false) // non-escaping
 		}
 		lvals[i] = lval
 	}
 	if len(lhss) == len(rhss) {
 		// Simple assignment:   x     = f()        (!isDef)
 		// Parallel assignment: x, y  = f(), g()   (!isDef)
 		// or short var decl:   x, y := f(), g()   (isDef)
 		//
 		// In all cases, the RHSs may refer to the LHSs,
 		// so we need a storebuf.
 		var sb storebuf
 		for i := range rhss {
 			b.assign(fn, lvals[i], rhss[i], isZero[i], &sb)
 		}
 		sb.emit(fn)
 	} else {
 		// e.g. x, y = pos()
 		tuple := b.exprN(fn, rhss[0])
 		emitDebugRef(fn, rhss[0], tuple, false)
 		for i, lval := range lvals {
 			lval.store(fn, emitExtract(fn, tuple, i))
 		}
 	}
 }
 
 // arrayLen returns the length of the array whose composite literal elements are elts.
 func (b *builder) arrayLen(fn *Function, elts []ast.Expr) int64 {
 	var max int64 = -1
 	var i int64 = -1
 	for _, e := range elts {
 		if kv, ok := e.(*ast.KeyValueExpr); ok {
 			i = b.expr(fn, kv.Key).(*Const).Int64()
 		} else {
 			i++
 		}
 		if i > max {
 			max = i
 		}
 	}
 	return max + 1
 }
 
 // compLit emits to fn code to initialize a composite literal e at
 // address addr with type typ.
 //
 // Nested composite literals are recursively initialized in place
 // where possible. If isZero is true, compLit assumes that addr
 // holds the zero value for typ.
 //
 // Because the elements of a composite literal may refer to the
 // variables being updated, as in the second line below,
 //
 //	x := T{a: 1}
 //	x = T{a: x.a}
 //
 // all the reads must occur before all the writes. Thus all stores to
 // loc are emitted to the storebuf sb for later execution.
 //
 // A CompositeLit may have pointer type only in the recursive (nested)
 // case when the type name is implicit.  e.g. in []*T{{}}, the inner
 // literal has type *T behaves like &T{}.
 // In that case, addr must hold a T, not a *T.
 func (b *builder) compLit(fn *Function, addr Value, e *ast.CompositeLit, isZero bool, sb *storebuf) {
 	typ := typeparams.Deref(fn.typeOf(e)) // retain the named/alias/param type, if any
 	switch t := typeparams.CoreType(typ).(type) {
 	case *types.Struct:
 		if !isZero && len(e.Elts) != t.NumFields() {
 			// memclear
 			zt := typeparams.MustDeref(addr.Type())
 			sb.store(&address{addr, e.Lbrace, nil}, zeroConst(zt))
 			isZero = true
 		}
 		var fIndices []int
 		for i, e := range e.Elts {
 			var (
 				pos   token.Pos
 				fType types.Type
 			)
 
 			if kv, ok := e.(*ast.KeyValueExpr); ok { // tagged field
 				fname := kv.Key.(*ast.Ident).Name
 				obj, index, _ := types.LookupFieldOrMethod(t, true, fn.declaredPackage().Pkg, fname)
 				fIndices = append(fIndices[:0], index...)
 				pos = kv.Colon
 				e = kv.Value
 				fType = obj.Type()
 			} else { // untagged field
 				fIndices = append(fIndices[:0], i)
 				pos = e.Pos()
 				fType = t.Field(i).Type()
 			}
 
 			last := len(fIndices) - 1
 			v := emitImplicitSelections(fn, addr, fIndices[:last], pos)
 
 			faddr := &FieldAddr{
 				X:     v,
 				Field: fIndices[last],
 			}
 			faddr.setPos(pos)
 			faddr.setType(types.NewPointer(fType))
 			fn.emit(faddr)
 			b.assign(fn, &address{addr: faddr, pos: pos, expr: e}, e, isZero, sb)
 		}
 
 	case *types.Array, *types.Slice:
 		var at *types.Array
 		var array Value
 		switch t := t.(type) {
 		case *types.Slice:
 			at = types.NewArray(t.Elem(), b.arrayLen(fn, e.Elts))
 			array = emitNew(fn, at, e.Lbrace, "slicelit")
 		case *types.Array:
 			at = t
 			array = addr
 
 			if !isZero && int64(len(e.Elts)) != at.Len() {
 				// memclear
 				zt := typeparams.MustDeref(array.Type())
 				sb.store(&address{array, e.Lbrace, nil}, zeroConst(zt))
 			}
 		}
 
 		var idx *Const
 		for _, e := range e.Elts {
 			pos := e.Pos()
 			if kv, ok := e.(*ast.KeyValueExpr); ok {
 				idx = b.expr(fn, kv.Key).(*Const)
 				pos = kv.Colon
 				e = kv.Value
 			} else {
 				var idxval int64
 				if idx != nil {
 					idxval = idx.Int64() + 1
 				}
 				idx = intConst(idxval)
 			}
 			iaddr := &IndexAddr{
 				X:     array,
 				Index: idx,
 			}
 			iaddr.setType(types.NewPointer(at.Elem()))
 			fn.emit(iaddr)
 			if t != at { // slice
 				// backing array is unaliased => storebuf not needed.
 				b.assign(fn, &address{addr: iaddr, pos: pos, expr: e}, e, true, nil)
 			} else {
 				b.assign(fn, &address{addr: iaddr, pos: pos, expr: e}, e, true, sb)
 			}
 		}
 
 		if t != at { // slice
 			s := &Slice{X: array}
 			s.setPos(e.Lbrace)
 			s.setType(typ)
 			sb.store(&address{addr: addr, pos: e.Lbrace, expr: e}, fn.emit(s))
 		}
 
 	case *types.Map:
 		m := &MakeMap{Reserve: intConst(int64(len(e.Elts)))}
 		m.setPos(e.Lbrace)
 		m.setType(typ)
 		fn.emit(m)
 		for _, e := range e.Elts {
 			e := e.(*ast.KeyValueExpr)
 
 			// If a key expression in a map literal is itself a
 			// composite literal, the type may be omitted.
 			// For example:
 			//	map[*struct{}]bool{{}: true}
 			// An &-operation may be implied:
 			//	map[*struct{}]bool{&struct{}{}: true}
 			wantAddr := false
 			if _, ok := ast.Unparen(e.Key).(*ast.CompositeLit); ok {
 				wantAddr = isPointerCore(t.Key())
 			}
 
 			var key Value
 			if wantAddr {
 				// A CompositeLit never evaluates to a pointer,
 				// so if the type of the location is a pointer,
 				// an &-operation is implied.
 				key = b.addr(fn, e.Key, true).address(fn)
 			} else {
 				key = b.expr(fn, e.Key)
 			}
 
 			loc := element{
 				m:   m,
 				k:   emitConv(fn, key, t.Key()),
 				t:   t.Elem(),
 				pos: e.Colon,
 			}
 
 			// We call assign() only because it takes care
 			// of any &-operation required in the recursive
 			// case, e.g.,
 			// map[int]*struct{}{0: {}} implies &struct{}{}.
 			// In-place update is of course impossible,
 			// and no storebuf is needed.
 			b.assign(fn, &loc, e.Value, true, nil)
 		}
 		sb.store(&address{addr: addr, pos: e.Lbrace, expr: e}, m)
 
 	default:
 		panic("unexpected CompositeLit type: " + typ.String())
 	}
 }
 
 // switchStmt emits to fn code for the switch statement s, optionally
 // labelled by label.
 func (b *builder) switchStmt(fn *Function, s *ast.SwitchStmt, label *lblock) {
 	// We treat SwitchStmt like a sequential if-else chain.
 	// Multiway dispatch can be recovered later by ssautil.Switches()
 	// to those cases that are free of side effects.
 	if s.Init != nil {
 		b.stmt(fn, s.Init)
 	}
 	var tag Value = vTrue
 	if s.Tag != nil {
 		tag = b.expr(fn, s.Tag)
 	}
 	done := fn.newBasicBlock("switch.done")
 	if label != nil {
 		label._break = done
 	}
 	// We pull the default case (if present) down to the end.
 	// But each fallthrough label must point to the next
 	// body block in source order, so we preallocate a
 	// body block (fallthru) for the next case.
 	// Unfortunately this makes for a confusing block order.
 	var dfltBody *[]ast.Stmt
 	var dfltFallthrough *BasicBlock
 	var fallthru, dfltBlock *BasicBlock
 	ncases := len(s.Body.List)
 	for i, clause := range s.Body.List {
 		body := fallthru
 		if body == nil {
 			body = fn.newBasicBlock("switch.body") // first case only
 		}
 
 		// Preallocate body block for the next case.
 		fallthru = done
 		if i+1 < ncases {
 			fallthru = fn.newBasicBlock("switch.body")
 		}
 
 		cc := clause.(*ast.CaseClause)
 		if cc.List == nil {
 			// Default case.
 			dfltBody = &cc.Body
 			dfltFallthrough = fallthru
 			dfltBlock = body
 			continue
 		}
 
 		var nextCond *BasicBlock
 		for _, cond := range cc.List {
 			nextCond = fn.newBasicBlock("switch.next")
 			// For boolean switches, emit short-circuit control flow,
 			// just like an if/else-chain.
 			if tag == vTrue && !isNonTypeParamInterface(fn.info.Types[cond].Type) {
 				b.cond(fn, cond, body, nextCond)
 			} else {
 				c := emitCompare(fn, token.EQL, tag, b.expr(fn, cond), cond.Pos())
 				emitIf(fn, c, body, nextCond)
 			}
 			fn.currentBlock = nextCond
 		}
 		fn.currentBlock = body
 		fn.targets = &targets{
 			tail:         fn.targets,
 			_break:       done,
 			_fallthrough: fallthru,
 		}
 		b.stmtList(fn, cc.Body)
 		fn.targets = fn.targets.tail
 		emitJump(fn, done)
 		fn.currentBlock = nextCond
 	}
 	if dfltBlock != nil {
 		emitJump(fn, dfltBlock)
 		fn.currentBlock = dfltBlock
 		fn.targets = &targets{
 			tail:         fn.targets,
 			_break:       done,
 			_fallthrough: dfltFallthrough,
 		}
 		b.stmtList(fn, *dfltBody)
 		fn.targets = fn.targets.tail
 	}
 	emitJump(fn, done)
 	fn.currentBlock = done
 }
 
 // typeSwitchStmt emits to fn code for the type switch statement s, optionally
 // labelled by label.
 func (b *builder) typeSwitchStmt(fn *Function, s *ast.TypeSwitchStmt, label *lblock) {
 	// We treat TypeSwitchStmt like a sequential if-else chain.
 	// Multiway dispatch can be recovered later by ssautil.Switches().
 
 	// Typeswitch lowering:
 	//
 	// var x X
 	// switch y := x.(type) {
 	// case T1, T2: S1                  // >1 	(y := x)
 	// case nil:    SN                  // nil 	(y := x)
 	// default:     SD                  // 0 types 	(y := x)
 	// case T3:     S3                  // 1 type 	(y := x.(T3))
 	// }
 	//
 	//      ...s.Init...
 	// 	x := eval x
 	// .caseT1:
 	// 	t1, ok1 := typeswitch,ok x <T1>
 	// 	if ok1 then goto S1 else goto .caseT2
 	// .caseT2:
 	// 	t2, ok2 := typeswitch,ok x <T2>
 	// 	if ok2 then goto S1 else goto .caseNil
 	// .S1:
 	//      y := x
 	// 	...S1...
 	// 	goto done
 	// .caseNil:
 	// 	if t2, ok2 := typeswitch,ok x <T2>
 	// 	if x == nil then goto SN else goto .caseT3
 	// .SN:
 	//      y := x
 	// 	...SN...
 	// 	goto done
 	// .caseT3:
 	// 	t3, ok3 := typeswitch,ok x <T3>
 	// 	if ok3 then goto S3 else goto default
 	// .S3:
 	//      y := t3
 	// 	...S3...
 	// 	goto done
 	// .default:
 	//      y := x
 	// 	...SD...
 	// 	goto done
 	// .done:
 	if s.Init != nil {
 		b.stmt(fn, s.Init)
 	}
 
 	var x Value
 	switch ass := s.Assign.(type) {
 	case *ast.ExprStmt: // x.(type)
 		x = b.expr(fn, ast.Unparen(ass.X).(*ast.TypeAssertExpr).X)
 	case *ast.AssignStmt: // y := x.(type)
 		x = b.expr(fn, ast.Unparen(ass.Rhs[0]).(*ast.TypeAssertExpr).X)
 	}
 
 	done := fn.newBasicBlock("typeswitch.done")
 	if label != nil {
 		label._break = done
 	}
 	var default_ *ast.CaseClause
 	for _, clause := range s.Body.List {
 		cc := clause.(*ast.CaseClause)
 		if cc.List == nil {
 			default_ = cc
 			continue
 		}
 		body := fn.newBasicBlock("typeswitch.body")
 		var next *BasicBlock
 		var casetype types.Type
 		var ti Value // ti, ok := typeassert,ok x <Ti>
 		for _, cond := range cc.List {
 			next = fn.newBasicBlock("typeswitch.next")
 			casetype = fn.typeOf(cond)
 			var condv Value
 			if casetype == tUntypedNil {
 				condv = emitCompare(fn, token.EQL, x, zeroConst(x.Type()), cond.Pos())
 				ti = x
 			} else {
 				yok := emitTypeTest(fn, x, casetype, cc.Case)
 				ti = emitExtract(fn, yok, 0)
 				condv = emitExtract(fn, yok, 1)
 			}
 			emitIf(fn, condv, body, next)
 			fn.currentBlock = next
 		}
 		if len(cc.List) != 1 {
 			ti = x
 		}
 		fn.currentBlock = body
 		b.typeCaseBody(fn, cc, ti, done)
 		fn.currentBlock = next
 	}
 	if default_ != nil {
 		b.typeCaseBody(fn, default_, x, done)
 	} else {
 		emitJump(fn, done)
 	}
 	fn.currentBlock = done
 }
 
 func (b *builder) typeCaseBody(fn *Function, cc *ast.CaseClause, x Value, done *BasicBlock) {
 	if obj, ok := fn.info.Implicits[cc].(*types.Var); ok {
 		// In a switch y := x.(type), each case clause
 		// implicitly declares a distinct object y.
 		// In a single-type case, y has that type.
 		// In multi-type cases, 'case nil' and default,
 		// y has the same type as the interface operand.
 		emitStore(fn, emitLocalVar(fn, obj), x, obj.Pos())
 	}
 	fn.targets = &targets{
 		tail:   fn.targets,
 		_break: done,
 	}
 	b.stmtList(fn, cc.Body)
 	fn.targets = fn.targets.tail
 	emitJump(fn, done)
 }
 
 // selectStmt emits to fn code for the select statement s, optionally
 // labelled by label.
 func (b *builder) selectStmt(fn *Function, s *ast.SelectStmt, label *lblock) {
 	// A blocking select of a single case degenerates to a
 	// simple send or receive.
 	// TODO(adonovan): opt: is this optimization worth its weight?
 	if len(s.Body.List) == 1 {
 		clause := s.Body.List[0].(*ast.CommClause)
 		if clause.Comm != nil {
 			b.stmt(fn, clause.Comm)
 			done := fn.newBasicBlock("select.done")
 			if label != nil {
 				label._break = done
 			}
 			fn.targets = &targets{
 				tail:   fn.targets,
 				_break: done,
 			}
 			b.stmtList(fn, clause.Body)
 			fn.targets = fn.targets.tail
 			emitJump(fn, done)
 			fn.currentBlock = done
 			return
 		}
 	}
 
 	// First evaluate all channels in all cases, and find
 	// the directions of each state.
 	var states []*SelectState
 	blocking := true
 	debugInfo := fn.debugInfo()
 	for _, clause := range s.Body.List {
 		var st *SelectState
 		switch comm := clause.(*ast.CommClause).Comm.(type) {
 		case nil: // default case
 			blocking = false
 			continue
 
 		case *ast.SendStmt: // ch<- i
 			ch := b.expr(fn, comm.Chan)
 			chtyp := typeparams.CoreType(fn.typ(ch.Type())).(*types.Chan)
 			st = &SelectState{
 				Dir:  types.SendOnly,
 				Chan: ch,
 				Send: emitConv(fn, b.expr(fn, comm.Value), chtyp.Elem()),
 				Pos:  comm.Arrow,
 			}
 			if debugInfo {
 				st.DebugNode = comm
 			}
 
 		case *ast.AssignStmt: // x := <-ch
 			recv := ast.Unparen(comm.Rhs[0]).(*ast.UnaryExpr)
 			st = &SelectState{
 				Dir:  types.RecvOnly,
 				Chan: b.expr(fn, recv.X),
 				Pos:  recv.OpPos,
 			}
 			if debugInfo {
 				st.DebugNode = recv
 			}
 
 		case *ast.ExprStmt: // <-ch
 			recv := ast.Unparen(comm.X).(*ast.UnaryExpr)
 			st = &SelectState{
 				Dir:  types.RecvOnly,
 				Chan: b.expr(fn, recv.X),
 				Pos:  recv.OpPos,
 			}
 			if debugInfo {
 				st.DebugNode = recv
 			}
 		}
 		states = append(states, st)
 	}
 
 	// We dispatch on the (fair) result of Select using a
 	// sequential if-else chain, in effect:
 	//
 	// idx, recvOk, r0...r_n-1 := select(...)
 	// if idx == 0 {  // receive on channel 0  (first receive => r0)
 	//     x, ok := r0, recvOk
 	//     ...state0...
 	// } else if v == 1 {   // send on channel 1
 	//     ...state1...
 	// } else {
 	//     ...default...
 	// }
 	sel := &Select{
 		States:   states,
 		Blocking: blocking,
 	}
 	sel.setPos(s.Select)
 	var vars []*types.Var
 	vars = append(vars, varIndex, varOk)
 	for _, st := range states {
 		if st.Dir == types.RecvOnly {
 			chtyp := typeparams.CoreType(fn.typ(st.Chan.Type())).(*types.Chan)
 			vars = append(vars, newVar("", chtyp.Elem()))
 		}
 	}
 	sel.setType(types.NewTuple(vars...))
 
 	fn.emit(sel)
 	idx := emitExtract(fn, sel, 0)
 
 	done := fn.newBasicBlock("select.done")
 	if label != nil {
 		label._break = done
 	}
 
 	var defaultBody *[]ast.Stmt
 	state := 0
 	r := 2 // index in 'sel' tuple of value; increments if st.Dir==RECV
 	for _, cc := range s.Body.List {
 		clause := cc.(*ast.CommClause)
 		if clause.Comm == nil {
 			defaultBody = &clause.Body
 			continue
 		}
 		body := fn.newBasicBlock("select.body")
 		next := fn.newBasicBlock("select.next")
 		emitIf(fn, emitCompare(fn, token.EQL, idx, intConst(int64(state)), token.NoPos), body, next)
 		fn.currentBlock = body
 		fn.targets = &targets{
 			tail:   fn.targets,
 			_break: done,
 		}
 		switch comm := clause.Comm.(type) {
 		case *ast.ExprStmt: // <-ch
 			if debugInfo {
 				v := emitExtract(fn, sel, r)
 				emitDebugRef(fn, states[state].DebugNode.(ast.Expr), v, false)
 			}
 			r++
 
 		case *ast.AssignStmt: // x := <-states[state].Chan
 			if comm.Tok == token.DEFINE {
 				emitLocalVar(fn, identVar(fn, comm.Lhs[0].(*ast.Ident)))
 			}
 			x := b.addr(fn, comm.Lhs[0], false) // non-escaping
 			v := emitExtract(fn, sel, r)
 			if debugInfo {
 				emitDebugRef(fn, states[state].DebugNode.(ast.Expr), v, false)
 			}
 			x.store(fn, v)
 
 			if len(comm.Lhs) == 2 { // x, ok := ...
 				if comm.Tok == token.DEFINE {
 					emitLocalVar(fn, identVar(fn, comm.Lhs[1].(*ast.Ident)))
 				}
 				ok := b.addr(fn, comm.Lhs[1], false) // non-escaping
 				ok.store(fn, emitExtract(fn, sel, 1))
 			}
 			r++
 		}
 		b.stmtList(fn, clause.Body)
 		fn.targets = fn.targets.tail
 		emitJump(fn, done)
 		fn.currentBlock = next
 		state++
 	}
 	if defaultBody != nil {
 		fn.targets = &targets{
 			tail:   fn.targets,
 			_break: done,
 		}
 		b.stmtList(fn, *defaultBody)
 		fn.targets = fn.targets.tail
 	} else {
 		// A blocking select must match some case.
 		// (This should really be a runtime.errorString, not a string.)
 		fn.emit(&Panic{
 			X: emitConv(fn, stringConst("blocking select matched no case"), tEface),
 		})
 		fn.currentBlock = fn.newBasicBlock("unreachable")
 	}
 	emitJump(fn, done)
 	fn.currentBlock = done
 }
 
 // forStmt emits to fn code for the for statement s, optionally
 // labelled by label.
 func (b *builder) forStmt(fn *Function, s *ast.ForStmt, label *lblock) {
 	// Use forStmtGo122 instead if it applies.
 	if s.Init != nil {
 		if assign, ok := s.Init.(*ast.AssignStmt); ok && assign.Tok == token.DEFINE {
 			if versions.AtLeast(fn.goversion, versions.Go1_22) {
 				b.forStmtGo122(fn, s, label)
 				return
 			}
 		}
 	}
 
 	//     ...init...
 	//     jump loop
 	// loop:
 	//     if cond goto body else done
 	// body:
 	//     ...body...
 	//     jump post
 	// post:                                 (target of continue)
 	//     ...post...
 	//     jump loop
 	// done:                                 (target of break)
 	if s.Init != nil {
 		b.stmt(fn, s.Init)
 	}
 
 	body := fn.newBasicBlock("for.body")
 	done := fn.newBasicBlock("for.done") // target of 'break'
 	loop := body                         // target of back-edge
 	if s.Cond != nil {
 		loop = fn.newBasicBlock("for.loop")
 	}
 	cont := loop // target of 'continue'
 	if s.Post != nil {
 		cont = fn.newBasicBlock("for.post")
 	}
 	if label != nil {
 		label._break = done
 		label._continue = cont
 	}
 	emitJump(fn, loop)
 	fn.currentBlock = loop
 	if loop != body {
 		b.cond(fn, s.Cond, body, done)
 		fn.currentBlock = body
 	}
 	fn.targets = &targets{
 		tail:      fn.targets,
 		_break:    done,
 		_continue: cont,
 	}
 	b.stmt(fn, s.Body)
 	fn.targets = fn.targets.tail
 	emitJump(fn, cont)
 
 	if s.Post != nil {
 		fn.currentBlock = cont
 		b.stmt(fn, s.Post)
 		emitJump(fn, loop) // back-edge
 	}
 	fn.currentBlock = done
 }
 
 // forStmtGo122 emits to fn code for the for statement s, optionally
 // labelled by label. s must define its variables.
 //
 // This allocates once per loop iteration. This is only correct in
 // GoVersions >= go1.22.
 func (b *builder) forStmtGo122(fn *Function, s *ast.ForStmt, label *lblock) {
 	//     i_outer = alloc[T]
 	//     *i_outer = ...init...        // under objects[i] = i_outer
 	//     jump loop
 	// loop:
 	//     i = phi [head: i_outer, loop: i_next]
 	//     ...cond...                   // under objects[i] = i
 	//     if cond goto body else done
 	// body:
 	//     ...body...                   // under objects[i] = i (same as loop)
 	//     jump post
 	// post:
 	//     tmp = *i
 	//     i_next = alloc[T]
 	//     *i_next = tmp
 	//     ...post...                   // under objects[i] = i_next
 	//     goto loop
 	// done:
 
 	init := s.Init.(*ast.AssignStmt)
 	startingBlocks := len(fn.Blocks)
 
 	pre := fn.currentBlock               // current block before starting
 	loop := fn.newBasicBlock("for.loop") // target of back-edge
 	body := fn.newBasicBlock("for.body")
 	post := fn.newBasicBlock("for.post") // target of 'continue'
 	done := fn.newBasicBlock("for.done") // target of 'break'
 
 	// For each of the n loop variables, we create five SSA values,
 	// outer, phi, next, load, and store in pre, loop, and post.
 	// There is no limit on n.
 	type loopVar struct {
 		obj   *types.Var
 		outer *Alloc
 		phi   *Phi
 		load  *UnOp
 		next  *Alloc
 		store *Store
 	}
 	vars := make([]loopVar, len(init.Lhs))
 	for i, lhs := range init.Lhs {
 		v := identVar(fn, lhs.(*ast.Ident))
 		typ := fn.typ(v.Type())
 
 		fn.currentBlock = pre
 		outer := emitLocal(fn, typ, v.Pos(), v.Name())
 
 		fn.currentBlock = loop
 		phi := &Phi{Comment: v.Name()}
 		phi.pos = v.Pos()
 		phi.typ = outer.Type()
 		fn.emit(phi)
 
 		fn.currentBlock = post
 		// If next is local, it reuses the address and zeroes the old value so
 		// load before allocating next.
 		load := emitLoad(fn, phi)
 		next := emitLocal(fn, typ, v.Pos(), v.Name())
 		store := emitStore(fn, next, load, token.NoPos)
 
 		phi.Edges = []Value{outer, next} // pre edge is emitted before post edge.
 
 		vars[i] = loopVar{v, outer, phi, load, next, store}
 	}
 
 	// ...init... under fn.objects[v] = i_outer
 	fn.currentBlock = pre
 	for _, v := range vars {
 		fn.vars[v.obj] = v.outer
 	}
 	const isDef = false // assign to already-allocated outers
 	b.assignStmt(fn, init.Lhs, init.Rhs, isDef)
 	if label != nil {
 		label._break = done
 		label._continue = post
 	}
 	emitJump(fn, loop)
 
 	// ...cond... under fn.objects[v] = i
 	fn.currentBlock = loop
 	for _, v := range vars {
 		fn.vars[v.obj] = v.phi
 	}
 	if s.Cond != nil {
 		b.cond(fn, s.Cond, body, done)
 	} else {
 		emitJump(fn, body)
 	}
 
 	// ...body... under fn.objects[v] = i
 	fn.currentBlock = body
 	fn.targets = &targets{
 		tail:      fn.targets,
 		_break:    done,
 		_continue: post,
 	}
 	b.stmt(fn, s.Body)
 	fn.targets = fn.targets.tail
 	emitJump(fn, post)
 
 	// ...post... under fn.objects[v] = i_next
 	for _, v := range vars {
 		fn.vars[v.obj] = v.next
 	}
 	fn.currentBlock = post
 	if s.Post != nil {
 		b.stmt(fn, s.Post)
 	}
 	emitJump(fn, loop) // back-edge
 	fn.currentBlock = done
 
 	// For each loop variable that does not escape,
 	// (the common case), fuse its next cells into its
 	// (local) outer cell as they have disjoint live ranges.
 	//
 	// It is sufficient to test whether i_next escapes,
 	// because its Heap flag will be marked true if either
 	// the cond or post expression causes i to escape
 	// (because escape distributes over phi).
 	var nlocals int
 	for _, v := range vars {
 		if !v.next.Heap {
 			nlocals++
 		}
 	}
 	if nlocals > 0 {
 		replace := make(map[Value]Value, 2*nlocals)
 		dead := make(map[Instruction]bool, 4*nlocals)
 		for _, v := range vars {
 			if !v.next.Heap {
 				replace[v.next] = v.outer
 				replace[v.phi] = v.outer
 				dead[v.phi], dead[v.next], dead[v.load], dead[v.store] = true, true, true, true
 			}
 		}
 
 		// Replace all uses of i_next and phi with i_outer.
 		// Referrers have not been built for fn yet so only update Instruction operands.
 		// We need only look within the blocks added by the loop.
 		var operands []*Value // recycle storage
 		for _, b := range fn.Blocks[startingBlocks:] {
 			for _, instr := range b.Instrs {
 				operands = instr.Operands(operands[:0])
 				for _, ptr := range operands {
 					k := *ptr
 					if v := replace[k]; v != nil {
 						*ptr = v
 					}
 				}
 			}
 		}
 
 		// Remove instructions for phi, load, and store.
 		// lift() will remove the unused i_next *Alloc.
 		isDead := func(i Instruction) bool { return dead[i] }
 		loop.Instrs = slices.DeleteFunc(loop.Instrs, isDead)
 		post.Instrs = slices.DeleteFunc(post.Instrs, isDead)
 	}
 }
 
 // rangeIndexed emits to fn the header for an integer-indexed loop
 // over array, *array or slice value x.
 // The v result is defined only if tv is non-nil.
 // forPos is the position of the "for" token.
 func (b *builder) rangeIndexed(fn *Function, x Value, tv types.Type, pos token.Pos) (k, v Value, loop, done *BasicBlock) {
 	//
 	//     length = len(x)
 	//     index = -1
 	// loop:                                     (target of continue)
 	//     index++
 	//     if index < length goto body else done
 	// body:
 	//     k = index
 	//     v = x[index]
 	//     ...body...
 	//     jump loop
 	// done:                                     (target of break)
 
 	// Determine number of iterations.
 	var length Value
 	dt := typeparams.Deref(x.Type())
 	if arr, ok := typeparams.CoreType(dt).(*types.Array); ok {
 		// For array or *array, the number of iterations is
 		// known statically thanks to the type.  We avoid a
 		// data dependence upon x, permitting later dead-code
 		// elimination if x is pure, static unrolling, etc.
 		// Ranging over a nil *array may have >0 iterations.
 		// We still generate code for x, in case it has effects.
 		length = intConst(arr.Len())
 	} else {
 		// length = len(x).
 		var c Call
 		c.Call.Value = makeLen(x.Type())
 		c.Call.Args = []Value{x}
 		c.setType(tInt)
 		length = fn.emit(&c)
 	}
 
 	index := emitLocal(fn, tInt, token.NoPos, "rangeindex")
 	emitStore(fn, index, intConst(-1), pos)
 
 	loop = fn.newBasicBlock("rangeindex.loop")
 	emitJump(fn, loop)
 	fn.currentBlock = loop
 
 	incr := &BinOp{
 		Op: token.ADD,
 		X:  emitLoad(fn, index),
 		Y:  vOne,
 	}
 	incr.setType(tInt)
 	emitStore(fn, index, fn.emit(incr), pos)
 
 	body := fn.newBasicBlock("rangeindex.body")
 	done = fn.newBasicBlock("rangeindex.done")
 	emitIf(fn, emitCompare(fn, token.LSS, incr, length, token.NoPos), body, done)
 	fn.currentBlock = body
 
 	k = emitLoad(fn, index)
 	if tv != nil {
 		switch t := typeparams.CoreType(x.Type()).(type) {
 		case *types.Array:
 			instr := &Index{
 				X:     x,
 				Index: k,
 			}
 			instr.setType(t.Elem())
 			instr.setPos(x.Pos())
 			v = fn.emit(instr)
 
 		case *types.Pointer: // *array
 			instr := &IndexAddr{
 				X:     x,
 				Index: k,
 			}
 			instr.setType(types.NewPointer(t.Elem().Underlying().(*types.Array).Elem()))
 			instr.setPos(x.Pos())
 			v = emitLoad(fn, fn.emit(instr))
 
 		case *types.Slice:
 			instr := &IndexAddr{
 				X:     x,
 				Index: k,
 			}
 			instr.setType(types.NewPointer(t.Elem()))
 			instr.setPos(x.Pos())
 			v = emitLoad(fn, fn.emit(instr))
 
 		default:
 			panic("rangeIndexed x:" + t.String())
 		}
 	}
 	return
 }
 
 // rangeIter emits to fn the header for a loop using
 // Range/Next/Extract to iterate over map or string value x.
 // tk and tv are the types of the key/value results k and v, or nil
 // if the respective component is not wanted.
 func (b *builder) rangeIter(fn *Function, x Value, tk, tv types.Type, pos token.Pos) (k, v Value, loop, done *BasicBlock) {
 	//
 	//     it = range x
 	// loop:                                   (target of continue)
 	//     okv = next it                       (ok, key, value)
 	//     ok = extract okv #0
 	//     if ok goto body else done
 	// body:
 	//     k = extract okv #1
 	//     v = extract okv #2
 	//     ...body...
 	//     jump loop
 	// done:                                   (target of break)
 	//
 
 	rng := &Range{X: x}
 	rng.setPos(pos)
 	rng.setType(tRangeIter)
 	it := fn.emit(rng)
 
 	loop = fn.newBasicBlock("rangeiter.loop")
 	emitJump(fn, loop)
 	fn.currentBlock = loop
 
 	var ak, av types.Type
 	isString := false
 	if m, ok := typeparams.CoreType(x.Type()).(*types.Map); ok {
 		ak, av = m.Key(), m.Elem()
 	} else {
 		isString = true
 		ak, av = tInt, tRune
 	}
 	if tk == nil {
 		ak = tInvalid
 	}
 	if tv == nil {
 		av = tInvalid
 	}
 
 	okv := &Next{
 		Iter:     it,
 		IsString: isString,
 	}
 	okv.setType(types.NewTuple(
 		varOk,
 		newVar("k", ak),
 		newVar("v", av),
 	))
 	fn.emit(okv)
 
 	body := fn.newBasicBlock("rangeiter.body")
 	done = fn.newBasicBlock("rangeiter.done")
 	emitIf(fn, emitExtract(fn, okv, 0), body, done)
 	fn.currentBlock = body
 
 	// The assignment may widen a map or string
 	// key/value to a variable's interface type
 	// (cases #1 and #2 of go.dev/issue/78110).
 	if tk != nil {
 		k = emitConv(fn, emitExtract(fn, okv, 1), tk)
 	}
 	if tv != nil {
 		v = emitConv(fn, emitExtract(fn, okv, 2), tv)
 	}
 	return
 }
 
 // rangeChan emits to fn the header for a loop that receives from
 // channel x until it fails.
 // tk is the channel's element type, or nil if the k result is
 // not wanted
 // pos is the position of the '=' or ':=' token.
 func (b *builder) rangeChan(fn *Function, x Value, tk types.Type, pos token.Pos) (k Value, loop, done *BasicBlock) {
 	//
 	// loop:                                   (target of continue)
 	//     ko = <-x                            (key, ok)
 	//     ok = extract ko #1
 	//     if ok goto body else done
 	// body:
 	//     k = extract ko #0
 	//     ...body...
 	//     goto loop
 	// done:                                   (target of break)
 
 	loop = fn.newBasicBlock("rangechan.loop")
 	emitJump(fn, loop)
 	fn.currentBlock = loop
 	recv := &UnOp{
 		Op:      token.ARROW,
 		X:       x,
 		CommaOk: true,
 	}
 	recv.setPos(pos)
 	recv.setType(types.NewTuple(
 		newVar("k", typeparams.CoreType(x.Type()).(*types.Chan).Elem()),
 		varOk,
 	))
 	ko := fn.emit(recv)
 	body := fn.newBasicBlock("rangechan.body")
 	done = fn.newBasicBlock("rangechan.done")
 	emitIf(fn, emitExtract(fn, ko, 1), body, done)
 	fn.currentBlock = body
 	if tk != nil {
 		k = emitExtract(fn, ko, 0)
 	}
 	return
 }
 
 // rangeInt emits to fn the header for a range loop with an integer operand.
 // tk is the key value's type, or nil if the k result is not wanted.
 // pos is the position of the "for" token.
 func (b *builder) rangeInt(fn *Function, x Value, tk types.Type, pos token.Pos) (k Value, loop, done *BasicBlock) {
 	//
 	//     iter = 0
 	//     if 0 < x goto body else done
 	// loop:                                   (target of continue)
 	//     iter++
 	//     if iter < x goto body else done
 	// body:
 	//     k = x
 	//     ...body...
 	//     jump loop
 	// done:                                   (target of break)
 
 	if isUntyped(x.Type()) {
 		x = emitConv(fn, x, tInt)
 	}
 
 	T := x.Type()
 	iter := emitLocal(fn, T, token.NoPos, "rangeint.iter")
 	// x may be unsigned. Avoid initializing x to -1.
 
 	body := fn.newBasicBlock("rangeint.body")
 	done = fn.newBasicBlock("rangeint.done")
 	emitIf(fn, emitCompare(fn, token.LSS, zeroConst(T), x, token.NoPos), body, done)
 
 	loop = fn.newBasicBlock("rangeint.loop")
 	fn.currentBlock = loop
 
 	incr := &BinOp{
 		Op: token.ADD,
 		X:  emitLoad(fn, iter),
 		Y:  emitConv(fn, vOne, T),
 	}
 	incr.setType(T)
 	emitStore(fn, iter, fn.emit(incr), pos)
 	emitIf(fn, emitCompare(fn, token.LSS, incr, x, token.NoPos), body, done)
 	fn.currentBlock = body
 
 	if tk != nil {
 		// Integer types (int, uint8, etc.) are named and
 		// we know that k is assignable to x when tk != nil.
 		// This implies tk and T are identical so no conversion is needed.
 		k = emitLoad(fn, iter)
 	}
 
 	return
 }
 
 // rangeStmt emits to fn code for the range statement s, optionally
 // labelled by label.
 func (b *builder) rangeStmt(fn *Function, s *ast.RangeStmt, label *lblock) {
 	var tk, tv types.Type
 	if s.Key != nil && !isBlankIdent(s.Key) {
 		tk = fn.typeOf(s.Key)
 	}
 	if s.Value != nil && !isBlankIdent(s.Value) {
 		tv = fn.typeOf(s.Value)
 	}
 
 	// create locals for s.Key and s.Value.
 	createVars := func() {
 		// Unlike a short variable declaration, a RangeStmt
 		// using := never redeclares an existing variable; it
 		// always creates a new one.
 		if tk != nil {
 			emitLocalVar(fn, identVar(fn, s.Key.(*ast.Ident)))
 		}
 		if tv != nil {
 			emitLocalVar(fn, identVar(fn, s.Value.(*ast.Ident)))
 		}
 	}
 
 	afterGo122 := versions.AtLeast(fn.goversion, versions.Go1_22)
 	if s.Tok == token.DEFINE && !afterGo122 {
 		// pre-go1.22: If iteration variables are defined (:=), this
 		// occurs once outside the loop.
 		createVars()
 	}
 
 	x := b.expr(fn, s.X)
 
 	var k, v Value
 	var loop, done *BasicBlock
 	switch rt := typeparams.CoreType(x.Type()).(type) {
 	case *types.Slice, *types.Array, *types.Pointer: // *array
 		k, v, loop, done = b.rangeIndexed(fn, x, tv, s.For)
 
 	case *types.Chan:
 		k, loop, done = b.rangeChan(fn, x, tk, s.For)
 
 	case *types.Map:
 		k, v, loop, done = b.rangeIter(fn, x, tk, tv, s.For)
 
 	case *types.Basic:
 		switch {
 		case rt.Info()&types.IsString != 0:
 			k, v, loop, done = b.rangeIter(fn, x, tk, tv, s.For)
 
 		case rt.Info()&types.IsInteger != 0:
 			k, loop, done = b.rangeInt(fn, x, tk, s.For)
 
 		default:
 			panic("Cannot range over basic type: " + rt.String())
 		}
 
 	case *types.Signature:
 		// Special case rewrite (fn.goversion >= go1.23):
 		// 	for x := range f { ... }
 		// into
 		// 	f(func(x T) bool { ... })
 		b.rangeFunc(fn, x, s, label)
 		return
 
 	default:
 		panic("Cannot range over: " + rt.String())
 	}
 
 	if s.Tok == token.DEFINE && afterGo122 {
 		// go1.22: If iteration variables are defined (:=), this occurs inside the loop.
 		createVars()
 	}
 
 	// Evaluate both LHS expressions before we update either.
 	var kl, vl lvalue
 	if tk != nil {
 		kl = b.addr(fn, s.Key, false) // non-escaping
 	}
 	if tv != nil {
 		vl = b.addr(fn, s.Value, false) // non-escaping
 	}
 	if tk != nil {
 		kl.store(fn, k)
 	}
 	if tv != nil {
 		vl.store(fn, v)
 	}
 
 	if label != nil {
 		label._break = done
 		label._continue = loop
 	}
 
 	fn.targets = &targets{
 		tail:      fn.targets,
 		_break:    done,
 		_continue: loop,
 	}
 	b.stmt(fn, s.Body)
 	fn.targets = fn.targets.tail
 	emitJump(fn, loop) // back-edge
 	fn.currentBlock = done
 }
 
 // rangeFunc emits to fn code for the range-over-func rng.Body of the iterator
 // function x, optionally labelled by label. It creates a new anonymous function
 // yield for rng and builds the function.
 func (b *builder) rangeFunc(fn *Function, x Value, rng *ast.RangeStmt, label *lblock) {
 	// Consider the SSA code for the outermost range-over-func in fn:
 	//
 	//   func fn(...) (ret R) {
 	//     ...
 	//     for k, v = range x {
 	// 	     ...
 	//     }
 	//     ...
 	//   }
 	//
 	// The code emitted into fn will look something like this.
 	//
 	// loop:
 	//     jump := READY
 	//     y := make closure yield [ret, deferstack, jump, k, v]
 	//     x(y)
 	//     switch jump {
 	//        [see resuming execution]
 	//     }
 	//     goto done
 	// done:
 	//     ...
 	//
 	// where yield is a new synthetic yield function:
 	//
 	// func yield(_k tk, _v tv) bool
 	//   free variables: [ret, stack, jump, k, v]
 	// {
 	//    entry:
 	//      if jump != READY then goto invalid else valid
 	//    invalid:
 	//      panic("iterator called when it is not in a ready state")
 	//    valid:
 	//      jump = BUSY
 	//      k = _k
 	//      v = _v
 	//    ...
 	//    cont:
 	//      jump = READY
 	//      return true
 	// }
 	//
 	// Yield state:
 	//
 	// Each range loop has an associated jump variable that records
 	// the state of the iterator. A yield function is initially
 	// in a READY (0) and callable state.  If the yield function is called
 	// and is not in READY state, it panics. When it is called in a callable
 	// state, it becomes BUSY. When execution reaches the end of the body
 	// of the loop (or a continue statement targeting the loop is executed),
 	// the yield function returns true and resumes being in a READY state.
 	// After the iterator function x(y) returns, then if the yield function
 	// is in a READY state, the yield enters the DONE state.
 	//
 	// Each lowered control statement (break X, continue X, goto Z, or return)
 	// that exits the loop sets the variable to a unique positive EXIT value,
 	// before returning false from the yield function.
 	//
 	// If the yield function returns abruptly due to a panic or GoExit,
 	// it remains in a BUSY state. The generated code asserts that, after
 	// the iterator call x(y) returns normally, the jump variable state
 	// is DONE.
 	//
 	// Resuming execution:
 	//
 	// The code generated for the range statement checks the jump
 	// variable to determine how to resume execution.
 	//
 	//    switch jump {
 	//    case BUSY:  panic("...")
 	//    case DONE:  goto done
 	//    case READY: state = DONE; goto done
 	//    case 123:   ... // action for exit 123.
 	//    case 456:   ... // action for exit 456.
 	//    ...
 	//    }
 	//
 	// Forward goto statements within a yield are jumps to labels that
 	// have not yet been traversed in fn. They may be in the Body of the
 	// function. What we emit for these is:
 	//
 	//    goto target
 	//  target:
 	//    ...
 	//
 	// We leave an unresolved exit in yield.exits to check at the end
 	// of building yield if it encountered target in the body. If it
 	// encountered target, no additional work is required. Otherwise,
 	// the yield emits a new early exit in the basic block for target.
 	// We expect that blockopt will fuse the early exit into the case
 	// block later. The unresolved exit is then added to yield.parent.exits.
 
 	loop := fn.newBasicBlock("rangefunc.loop")
 	done := fn.newBasicBlock("rangefunc.done")
 
 	// These are targets within y.
 	fn.targets = &targets{
 		tail:   fn.targets,
 		_break: done,
 		// _continue is within y.
 	}
 	if label != nil {
 		label._break = done
 		// _continue is within y
 	}
 
 	emitJump(fn, loop)
 	fn.currentBlock = loop
 
 	// loop:
 	//     jump := READY
 
 	anonIdx := len(fn.AnonFuncs)
 
 	jump := newVar(fmt.Sprintf("jump$%d", anonIdx+1), tInt)
 	emitLocalVar(fn, jump) // zero value is READY
 
 	xsig := typeparams.CoreType(x.Type()).(*types.Signature)
 	ysig := typeparams.CoreType(xsig.Params().At(0).Type()).(*types.Signature)
 
 	/* synthetic yield function for body of range-over-func loop */
 	y := &Function{
 		name:           fmt.Sprintf("%s$%d", fn.Name(), anonIdx+1),
 		Signature:      ysig,
 		Synthetic:      "range-over-func yield",
 		pos:            rng.Range,
 		parent:         fn,
 		anonIdx:        int32(len(fn.AnonFuncs)),
 		Pkg:            fn.Pkg,
 		Prog:           fn.Prog,
 		syntax:         rng,
 		info:           fn.info,
 		goversion:      fn.goversion,
 		build:          (*builder).buildYieldFunc,
 		topLevelOrigin: nil,
 		typeparams:     fn.typeparams,
 		typeargs:       fn.typeargs,
 		subst:          fn.subst,
 		jump:           jump,
 		deferstack:     fn.deferstack,
 		returnVars:     fn.returnVars, // use the parent's return variables
 		uniq:           fn.uniq,       // start from parent's unique values
 	}
 
 	// If the RangeStmt has a label, this is how it is passed to buildYieldFunc.
 	if label != nil {
 		y.lblocks = map[*types.Label]*lblock{label.label: nil}
 	}
 	fn.AnonFuncs = append(fn.AnonFuncs, y)
 
 	// Build y immediately. It may:
 	// * cause fn's locals to escape, and
 	// * create new exit nodes in exits.
 	// (y is not marked 'built' until the end of the enclosing FuncDecl.)
 	unresolved := len(fn.exits)
 	y.build(b, y)
 	fn.uniq = y.uniq // resume after y's unique values
 
 	// Emit the call of y.
 	//   c := MakeClosure y
 	//   x(c)
 	c := &MakeClosure{Fn: y}
 	c.setType(ysig)
 	for _, fv := range y.FreeVars {
 		c.Bindings = append(c.Bindings, fv.outer)
 		fv.outer = nil
 	}
 	fn.emit(c)
 	call := Call{
 		Call: CallCommon{
 			Value: x,
 			Args:  []Value{c},
 			pos:   token.NoPos,
 		},
 	}
 	call.setType(xsig.Results())
 	fn.emit(&call)
 
 	exits := fn.exits[unresolved:]
 	b.buildYieldResume(fn, jump, exits, done)
 
 	emitJump(fn, done)
 	fn.currentBlock = done
 	// pop the stack for the range-over-func
 	fn.targets = fn.targets.tail
 }
 
 // buildYieldResume emits to fn code for how to resume execution once a call to
 // the iterator function over the yield function returns x(y). It does this by building
 // a switch over the value of jump for when it is READY, BUSY, or EXIT(id).
 func (b *builder) buildYieldResume(fn *Function, jump *types.Var, exits []*exit, done *BasicBlock) {
 	//    v := *jump
 	//    switch v {
 	//    case BUSY:    panic("...")
 	//    case READY:   jump = DONE; goto done
 	//    case EXIT(a): ...
 	//    case EXIT(b): ...
 	//    ...
 	//    }
 	v := emitLoad(fn, fn.lookup(jump, false))
 
 	// case BUSY: panic("...")
 	isbusy := fn.newBasicBlock("rangefunc.resume.busy")
 	ifready := fn.newBasicBlock("rangefunc.resume.ready.check")
 	emitIf(fn, emitCompare(fn, token.EQL, v, jBusy, token.NoPos), isbusy, ifready)
 	fn.currentBlock = isbusy
 	fn.emit(&Panic{
 		X: emitConv(fn, stringConst("iterator call did not preserve panic"), tEface),
 	})
 	fn.currentBlock = ifready
 
 	// case READY: jump = DONE; goto done
 	isready := fn.newBasicBlock("rangefunc.resume.ready")
 	ifexit := fn.newBasicBlock("rangefunc.resume.exits")
 	emitIf(fn, emitCompare(fn, token.EQL, v, jReady, token.NoPos), isready, ifexit)
 	fn.currentBlock = isready
 	storeVar(fn, jump, jDone, token.NoPos)
 	emitJump(fn, done)
 	fn.currentBlock = ifexit
 
 	for _, e := range exits {
 		id := intConst(e.id)
 
 		//  case EXIT(id): { /* do e */ }
 		cond := emitCompare(fn, token.EQL, v, id, e.pos)
 		matchb := fn.newBasicBlock("rangefunc.resume.match")
 		cndb := fn.newBasicBlock("rangefunc.resume.cnd")
 		emitIf(fn, cond, matchb, cndb)
 		fn.currentBlock = matchb
 
 		// Cases to fill in the { /* do e */ } bit.
 		switch {
 		case e.label != nil: // forward goto?
 			// case EXIT(id): goto lb // label
 			lb := fn.lblockOf(e.label)
 			// Do not mark lb as resolved.
 			// If fn does not contain label, lb remains unresolved and
 			// fn must itself be a range-over-func function. lb will be:
 			//   lb:
 			//     fn.jump = id
 			//     return false
 			emitJump(fn, lb._goto)
 
 		case e.to != fn: // e jumps to an ancestor of fn?
 			// case EXIT(id): { fn.jump = id; return false }
 			// fn is a range-over-func function.
 			storeVar(fn, fn.jump, id, token.NoPos)
 			fn.emit(&Return{Results: []Value{vFalse}, pos: e.pos})
 
 		case e.block == nil && e.label == nil: // return from fn?
 			// case EXIT(id): { return ... }
 			fn.emit(new(RunDefers))
 			results := make([]Value, len(fn.results))
 			for i, r := range fn.results {
 				results[i] = emitLoad(fn, r)
 			}
 			fn.emit(&Return{Results: results, pos: e.pos})
 
 		case e.block != nil:
 			// case EXIT(id): goto block
 			emitJump(fn, e.block)
 
 		default:
 			panic("unreachable")
 		}
 		fn.currentBlock = cndb
 	}
 }
 
 // stmt lowers statement s to SSA form, emitting code to fn.
 func (b *builder) stmt(fn *Function, _s ast.Stmt) {
 	// The label of the current statement.  If non-nil, its _goto
 	// target is always set; its _break and _continue are set only
 	// within the body of switch/typeswitch/select/for/range.
 	// It is effectively an additional default-nil parameter of stmt().
 	var label *lblock
 start:
 	switch s := _s.(type) {
 	case *ast.EmptyStmt:
 		// ignore.  (Usually removed by gofmt.)
 
 	case *ast.DeclStmt: // Con, Var or Typ
 		d := s.Decl.(*ast.GenDecl)
 		if d.Tok == token.VAR {
 			for _, spec := range d.Specs {
 				if vs, ok := spec.(*ast.ValueSpec); ok {
 					b.localValueSpec(fn, vs)
 				}
 			}
 		}
 
 	case *ast.LabeledStmt:
 		if s.Label.Name == "_" {
 			// Blank labels can't be the target of a goto, break,
 			// or continue statement, so we don't need a new block.
 			_s = s.Stmt
 			goto start
 		}
 		label = fn.lblockOf(fn.label(s.Label))
 		label.resolved = true
 		emitJump(fn, label._goto)
 		fn.currentBlock = label._goto
 		_s = s.Stmt
 		goto start // effectively: tailcall stmt(fn, s.Stmt, label)
 
 	case *ast.ExprStmt:
 		b.expr(fn, s.X)
 
 	case *ast.SendStmt:
 		chtyp := typeparams.CoreType(fn.typeOf(s.Chan)).(*types.Chan)
 		fn.emit(&Send{
 			Chan: b.expr(fn, s.Chan),
 			X:    emitConv(fn, b.expr(fn, s.Value), chtyp.Elem()),
 			pos:  s.Arrow,
 		})
 
 	case *ast.IncDecStmt:
 		op := token.ADD
 		if s.Tok == token.DEC {
 			op = token.SUB
 		}
 		loc := b.addr(fn, s.X, false)
 		b.assignOp(fn, loc, NewConst(constant.MakeInt64(1), loc.typ()), op, s.Pos())
 
 	case *ast.AssignStmt:
 		switch s.Tok {
 		case token.ASSIGN, token.DEFINE:
 			b.assignStmt(fn, s.Lhs, s.Rhs, s.Tok == token.DEFINE)
 
 		default: // +=, etc.
 			op := s.Tok + token.ADD - token.ADD_ASSIGN
 			b.assignOp(fn, b.addr(fn, s.Lhs[0], false), b.expr(fn, s.Rhs[0]), op, s.Pos())
 		}
 
 	case *ast.GoStmt:
 		// The "intrinsics" new/make/len/cap are forbidden here.
 		// panic is treated like an ordinary function call.
 		v := Go{pos: s.Go}
 		b.setCall(fn, s.Call, &v.Call)
 		fn.emit(&v)
 
 	case *ast.DeferStmt:
 		// The "intrinsics" new/make/len/cap are forbidden here.
 		// panic is treated like an ordinary function call.
 		deferstack := emitLoad(fn, fn.lookup(fn.deferstack, false))
 		v := Defer{pos: s.Defer, DeferStack: deferstack}
 		b.setCall(fn, s.Call, &v.Call)
 		fn.emit(&v)
 
 		// A deferred call can cause recovery from panic,
 		// and control resumes at the Recover block.
 		createRecoverBlock(fn.source)
 
 	case *ast.ReturnStmt:
 		b.returnStmt(fn, s)
 
 	case *ast.BranchStmt:
 		b.branchStmt(fn, s)
 
 	case *ast.BlockStmt:
 		b.stmtList(fn, s.List)
 
 	case *ast.IfStmt:
 		if s.Init != nil {
 			b.stmt(fn, s.Init)
 		}
 		then := fn.newBasicBlock("if.then")
 		done := fn.newBasicBlock("if.done")
 		els := done
 		if s.Else != nil {
 			els = fn.newBasicBlock("if.else")
 		}
 		b.cond(fn, s.Cond, then, els)
 		fn.currentBlock = then
 		b.stmt(fn, s.Body)
 		emitJump(fn, done)
 
 		if s.Else != nil {
 			fn.currentBlock = els
 			b.stmt(fn, s.Else)
 			emitJump(fn, done)
 		}
 
 		fn.currentBlock = done
 
 	case *ast.SwitchStmt:
 		b.switchStmt(fn, s, label)
 
 	case *ast.TypeSwitchStmt:
 		b.typeSwitchStmt(fn, s, label)
 
 	case *ast.SelectStmt:
 		b.selectStmt(fn, s, label)
 
 	case *ast.ForStmt:
 		b.forStmt(fn, s, label)
 
 	case *ast.RangeStmt:
 		b.rangeStmt(fn, s, label)
 
 	default:
 		panic(fmt.Sprintf("unexpected statement kind: %T", s))
 	}
 }
 
 func (b *builder) branchStmt(fn *Function, s *ast.BranchStmt) {
 	var block *BasicBlock
 	if s.Label == nil {
 		block = targetedBlock(fn, s.Tok)
 	} else {
 		target := fn.label(s.Label)
 		block = labelledBlock(fn, target, s.Tok)
 		if block == nil { // forward goto
 			lb := fn.lblockOf(target)
 			block = lb._goto // jump to lb._goto
 			if fn.jump != nil {
 				// fn is a range-over-func and the goto may exit fn.
 				// Create an exit and resolve it at the end of
 				// builder.buildYieldFunc.
 				labelExit(fn, target, s.Pos())
 			}
 		}
 	}
 	to := block.parent
 
 	if to == fn {
 		emitJump(fn, block)
 	} else { // break outside of fn.
 		// fn must be a range-over-func
 		e := blockExit(fn, block, s.Pos())
 		storeVar(fn, fn.jump, intConst(e.id), e.pos)
 		fn.emit(&Return{Results: []Value{vFalse}, pos: e.pos})
 	}
 	fn.currentBlock = fn.newBasicBlock("unreachable")
 }
 
 func (b *builder) returnStmt(fn *Function, s *ast.ReturnStmt) {
 	var results []Value
 
 	sig := fn.source.Signature // signature of the enclosing source function
 
 	// Convert return operands to result type.
 	if len(s.Results) == 1 && sig.Results().Len() > 1 {
 		// Return of one expression in a multi-valued function.
 		tuple := b.exprN(fn, s.Results[0])
 		ttuple := tuple.Type().(*types.Tuple)
 		for i, n := 0, ttuple.Len(); i < n; i++ {
 			results = append(results,
 				emitConv(fn, emitExtract(fn, tuple, i),
 					sig.Results().At(i).Type()))
 		}
 	} else {
 		// 1:1 return, or no-arg return in non-void function.
 		for i, r := range s.Results {
 			v := emitConv(fn, b.expr(fn, r), sig.Results().At(i).Type())
 			results = append(results, v)
 		}
 	}
 
 	// Store the results.
 	for i, r := range results {
 		var result Value // fn.source.result[i] conceptually
 		if fn == fn.source {
 			result = fn.results[i]
 		} else { // lookup needed?
 			result = fn.lookup(fn.returnVars[i], false)
 		}
 		emitStore(fn, result, r, s.Return)
 	}
 
 	if fn.jump != nil {
 		// Return from body of a range-over-func.
 		// The return statement is syntactically within the loop,
 		// but the generated code is in the 'switch jump {...}' after it.
 		e := returnExit(fn, s.Pos())
 		storeVar(fn, fn.jump, intConst(e.id), e.pos)
 		fn.emit(&Return{Results: []Value{vFalse}, pos: e.pos})
 		fn.currentBlock = fn.newBasicBlock("unreachable")
 		return
 	}
 
 	// Run function calls deferred in this
 	// function when explicitly returning from it.
 	fn.emit(new(RunDefers))
 	// Reload (potentially) named result variables to form the result tuple.
 	results = results[:0]
 	for _, nr := range fn.results {
 		results = append(results, emitLoad(fn, nr))
 	}
 	fn.emit(&Return{Results: results, pos: s.Return})
 	fn.currentBlock = fn.newBasicBlock("unreachable")
 }
 
 // A buildFunc is a strategy for building the SSA body for a function.
 type buildFunc = func(*builder, *Function)
 
 // iterate causes all created but unbuilt functions to be built. As
 // this may create new methods, the process is iterated until it
 // converges.
 //
 // Waits for any dependencies to finish building.
 func (b *builder) iterate() {
 	for ; b.finished < len(b.fns); b.finished++ {
 		fn := b.fns[b.finished]
 		b.buildFunction(fn)
 	}
 
 	b.buildshared.markDone()
 	b.buildshared.wait()
 }
 
 // buildFunction builds SSA code for the body of function fn.  Idempotent.
 func (b *builder) buildFunction(fn *Function) {
 	if fn.build != nil {
 		assert(fn.parent == nil, "anonymous functions should not be built by buildFunction()")
 
 		if fn.Prog.mode&LogSource != 0 {
 			defer logStack("build %s @ %s", fn, fn.Prog.Fset.Position(fn.pos))()
 		}
 		fn.build(b, fn)
 		fn.done()
 	}
 }
 
 // buildParamsOnly builds fn.Params from fn.Signature, but does not build fn.Body.
 func (b *builder) buildParamsOnly(fn *Function) {
 	// For external (C, asm) functions or functions loaded from
 	// export data, we must set fn.Params even though there is no
 	// body code to reference them.
 	if recv := fn.Signature.Recv(); recv != nil {
 		fn.addParamVar(recv)
 	}
 	params := fn.Signature.Params()
 	for i, n := 0, params.Len(); i < n; i++ {
 		fn.addParamVar(params.At(i))
 	}
 
 	// clear out other function state (keep consistent with finishBody)
 	fn.subst = nil
 }
 
 // buildFromSyntax builds fn.Body from fn.syntax, which must be non-nil.
 func (b *builder) buildFromSyntax(fn *Function) {
 	var (
 		recvField *ast.FieldList
 		body      *ast.BlockStmt
 		functype  *ast.FuncType
 	)
 	switch syntax := fn.syntax.(type) {
 	case *ast.FuncDecl:
 		functype = syntax.Type
 		recvField = syntax.Recv
 		body = syntax.Body
 		if body == nil {
 			b.buildParamsOnly(fn) // no body (non-Go function)
 			return
 		}
 	case *ast.FuncLit:
 		functype = syntax.Type
 		body = syntax.Body
 	case nil:
 		panic("no syntax")
 	default:
 		panic(syntax) // unexpected syntax
 	}
 	fn.source = fn
 	fn.startBody()
 	fn.createSyntacticParams(recvField, functype)
 	fn.createDeferStack()
 	b.stmt(fn, body)
 	if cb := fn.currentBlock; cb != nil && (cb == fn.Blocks[0] || cb == fn.Recover || cb.Preds != nil) {
 		// Control fell off the end of the function's body block.
 		//
 		// Block optimizations eliminate the current block, if
 		// unreachable.  It is a builder invariant that
 		// if this no-arg return is ill-typed for
 		// fn.Signature.Results, this block must be
 		// unreachable.  The sanity checker checks this.
 		fn.emit(new(RunDefers))
 		fn.emit(new(Return))
 	}
 	fn.finishBody()
 }
 
 // buildYieldFunc builds the body of the yield function created
 // from a range-over-func *ast.RangeStmt.
 func (b *builder) buildYieldFunc(fn *Function) {
 	// See builder.rangeFunc for detailed documentation on how fn is set up.
 	//
 	// In pseudo-Go this roughly builds:
 	// func yield(_k tk, _v tv) bool {
 	// 	   if jump != READY { panic("yield function called after range loop exit") }
 	//     jump = BUSY
 	//     k, v = _k, _v // assign the iterator variable (if needed)
 	//     ... // rng.Body
 	//   continue:
 	//     jump = READY
 	//     return true
 	// }
 	s := fn.syntax.(*ast.RangeStmt)
 	fn.source = fn.parent.source
 	fn.startBody()
 	params := fn.Signature.Params()
 	for v := range params.Variables() {
 		fn.addParamVar(v)
 	}
 
 	// Initial targets
 	ycont := fn.newBasicBlock("yield-continue")
 	// lblocks is either {} or is {label: nil} where label is the label of syntax.
 	for label := range fn.lblocks {
 		fn.lblocks[label] = &lblock{
 			label:     label,
 			resolved:  true,
 			_goto:     ycont,
 			_continue: ycont,
 			// `break label` statement targets fn.parent.targets._break
 		}
 	}
 	fn.targets = &targets{
 		tail:      fn.targets,
 		_continue: ycont,
 		// `break` statement targets fn.parent.targets._break.
 	}
 
 	// continue:
 	//   jump = READY
 	//   return true
 	saved := fn.currentBlock
 	fn.currentBlock = ycont
 	storeVar(fn, fn.jump, jReady, s.Body.Rbrace)
 	// A yield function's own deferstack is always empty, so rundefers is not needed.
 	fn.emit(&Return{Results: []Value{vTrue}, pos: token.NoPos})
 
 	// Emit header:
 	//
 	//   if jump != READY { panic("yield iterator accessed after exit") }
 	//   jump = BUSY
 	//   k, v = _k, _v
 	fn.currentBlock = saved
 	yloop := fn.newBasicBlock("yield-loop")
 	invalid := fn.newBasicBlock("yield-invalid")
 
 	jumpVal := emitLoad(fn, fn.lookup(fn.jump, true))
 	emitIf(fn, emitCompare(fn, token.EQL, jumpVal, jReady, token.NoPos), yloop, invalid)
 	fn.currentBlock = invalid
 	fn.emit(&Panic{
 		X: emitConv(fn, stringConst("yield function called after range loop exit"), tEface),
 	})
 
 	fn.currentBlock = yloop
 	storeVar(fn, fn.jump, jBusy, s.Body.Rbrace)
 
 	// Initialize k and v from params.
 	var tk, tv types.Type
 	if s.Key != nil && !isBlankIdent(s.Key) {
 		tk = fn.typeOf(s.Key) // fn.parent.typeOf is identical
 	}
 	if s.Value != nil && !isBlankIdent(s.Value) {
 		tv = fn.typeOf(s.Value)
 	}
 	if s.Tok == token.DEFINE {
 		if tk != nil {
 			emitLocalVar(fn, identVar(fn, s.Key.(*ast.Ident)))
 		}
 		if tv != nil {
 			emitLocalVar(fn, identVar(fn, s.Value.(*ast.Ident)))
 		}
 	}
 	var k, v Value
 	if len(fn.Params) > 0 {
 		k = fn.Params[0]
 	}
 	if len(fn.Params) > 1 {
 		v = fn.Params[1]
 	}
 	var kl, vl lvalue
 	if tk != nil {
 		kl = b.addr(fn, s.Key, false) // non-escaping
 	}
 	if tv != nil {
 		vl = b.addr(fn, s.Value, false) // non-escaping
 	}
 	if tk != nil {
 		kl.store(fn, k)
 	}
 	if tv != nil {
 		vl.store(fn, v)
 	}
 
 	// Build the body of the range loop.
 	b.stmt(fn, s.Body)
 	if cb := fn.currentBlock; cb != nil && (cb == fn.Blocks[0] || cb == fn.Recover || cb.Preds != nil) {
 		// Control fell off the end of the function's body block.
 		// Block optimizations eliminate the current block, if
 		// unreachable.
 		emitJump(fn, ycont)
 	}
 	// pop the stack for the yield function
 	fn.targets = fn.targets.tail
 
 	// Clean up exits and promote any unresolved exits to fn.parent.
 	for _, e := range fn.exits {
 		if e.label != nil {
 			lb := fn.lblocks[e.label]
 			if lb.resolved {
 				// label was resolved. Do not turn lb into an exit.
 				// e does not need to be handled by the parent.
 				continue
 			}
 
 			// _goto becomes an exit.
 			//   _goto:
 			//     jump = id
 			//     return false
 			fn.currentBlock = lb._goto
 			id := intConst(e.id)
 			storeVar(fn, fn.jump, id, e.pos)
 			fn.emit(&Return{Results: []Value{vFalse}, pos: e.pos})
 		}
 
 		if e.to != fn { // e needs to be handled by the parent too.
 			fn.parent.exits = append(fn.parent.exits, e)
 		}
 	}
 
 	fn.finishBody()
 }
 
 // addMakeInterfaceType records non-interface type t as the type of
 // the operand a MakeInterface operation, for [Program.RuntimeTypes].
 //
 // Acquires prog.makeInterfaceTypesMu.
 func addMakeInterfaceType(prog *Program, t types.Type) {
 	prog.makeInterfaceTypesMu.Lock()
 	defer prog.makeInterfaceTypesMu.Unlock()
 	if prog.makeInterfaceTypes == nil {
 		prog.makeInterfaceTypes = make(map[types.Type]unit)
 	}
 	prog.makeInterfaceTypes[t] = unit{}
 }
 
 // Build calls Package.Build for each package in prog.
 // Building occurs in parallel unless the BuildSerially mode flag was set.
 //
 // Build is intended for whole-program analysis; a typical compiler
 // need only build a single package.
 //
 // Build is idempotent and thread-safe.
 func (prog *Program) Build() {
 	var wg sync.WaitGroup
 	for _, p := range prog.packages {
 		if prog.mode&BuildSerially != 0 {
 			p.Build()
 		} else {
 			wg.Add(1)
 			cpuLimit <- unit{} // acquire a token
 			go func(p *Package) {
 				p.Build()
 				wg.Done()
 				<-cpuLimit // release a token
 			}(p)
 		}
 	}
 	wg.Wait()
 }
 
 // cpuLimit is a counting semaphore to limit CPU parallelism.
 var cpuLimit = make(chan unit, runtime.GOMAXPROCS(0))
 
 // Build builds SSA code for all functions and vars in package p.
 //
 // CreatePackage must have been called for all of p's direct imports
 // (and hence its direct imports must have been error-free). It is not
 // necessary to call CreatePackage for indirect dependencies.
 // Functions will be created for all necessary methods in those
 // packages on demand.
 //
 // Build is idempotent and thread-safe.
 func (p *Package) Build() { p.buildOnce.Do(p.build) }
 
 func (p *Package) build() {
 	if p.info == nil {
 		return // synthetic package, e.g. "testmain"
 	}
 	if p.Prog.mode&LogSource != 0 {
 		defer logStack("build %s", p)()
 	}
 
 	b := builder{fns: p.created}
 	b.iterate()
 
 	// We no longer need transient information: ASTs or go/types deductions.
 	p.info = nil
 	p.created = nil
 	p.files = nil
 	p.initVersion = nil
 
 	if p.Prog.mode&SanityCheckFunctions != 0 {
 		sanityCheckPackage(p)
 	}
 }
 
 // buildPackageInit builds fn.Body for the synthetic package initializer.
 func (b *builder) buildPackageInit(fn *Function) {
 	p := fn.Pkg
 	fn.startBody()
 
 	var done *BasicBlock
 
 	if p.Prog.mode&BareInits == 0 {
 		// Make init() skip if package is already initialized.
 		initguard := p.Var("init$guard")
 		doinit := fn.newBasicBlock("init.start")
 		done = fn.newBasicBlock("init.done")
 		emitIf(fn, emitLoad(fn, initguard), done, doinit)
 		fn.currentBlock = doinit
 		emitStore(fn, initguard, vTrue, token.NoPos)
 
 		// Call the init() function of each package we import.
 		for _, pkg := range p.Pkg.Imports() {
 			prereq := p.Prog.packages[pkg]
 			if prereq == nil {
 				panic(fmt.Sprintf("Package(%q).Build(): unsatisfied import: Program.CreatePackage(%q) was not called", p.Pkg.Path(), pkg.Path()))
 			}
 			var v Call
 			v.Call.Value = prereq.init
 			v.Call.pos = fn.pos
 			v.setType(types.NewTuple())
 			fn.emit(&v)
 		}
 	}
 
 	// Initialize package-level vars in correct order.
 	if len(p.info.InitOrder) > 0 && len(p.files) == 0 {
 		panic("no source files provided for package. cannot initialize globals")
 	}
 
 	for _, varinit := range p.info.InitOrder {
 		if fn.Prog.mode&LogSource != 0 {
 			fmt.Fprintf(os.Stderr, "build global initializer %v @ %s\n",
 				varinit.Lhs, p.Prog.Fset.Position(varinit.Rhs.Pos()))
 		}
 		// Initializers for global vars are evaluated in dependency
 		// order, but may come from arbitrary files of the package
 		// with different versions, so we transiently update
 		// fn.goversion for each one. (Since init is a synthetic
 		// function it has no syntax of its own that needs a version.)
 		fn.goversion = p.initVersion[varinit.Rhs]
 		if len(varinit.Lhs) == 1 {
 			// 1:1 initialization: var x, y = a(), b()
 			var lval lvalue
 			if v := varinit.Lhs[0]; v.Name() != "_" {
 				lval = &address{addr: p.objects[v].(*Global), pos: v.Pos()}
 			} else {
 				lval = blank{}
 			}
 			b.assign(fn, lval, varinit.Rhs, true, nil)
 		} else {
 			// n:1 initialization: var x, y :=  f()
 			tuple := b.exprN(fn, varinit.Rhs)
 			for i, v := range varinit.Lhs {
 				if v.Name() == "_" {
 					continue
 				}
 				emitStore(fn, p.objects[v].(*Global), emitExtract(fn, tuple, i), v.Pos())
 			}
 		}
 	}
 
 	// The rest of the init function is synthetic:
 	// no syntax, info, goversion.
 	fn.info = nil
 	fn.goversion = ""
 
 	// Call all of the declared init() functions in source order.
 	for _, file := range p.files {
 		for _, decl := range file.Decls {
 			if decl, ok := decl.(*ast.FuncDecl); ok {
 				id := decl.Name
 				if !isBlankIdent(id) && id.Name == "init" && decl.Recv == nil {
 					declaredInit := p.objects[p.info.Defs[id]].(*Function)
 					var v Call
 					v.Call.Value = declaredInit
 					v.setType(types.NewTuple())
 					p.init.emit(&v)
 				}
 			}
 		}
 	}
 
 	// Finish up init().
 	if p.Prog.mode&BareInits == 0 {
 		emitJump(fn, done)
 		fn.currentBlock = done
 	}
 	fn.emit(new(Return))
 	fn.finishBody()
 }