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// Copyright 2014 The llgo Authors.
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
package ssaopt
import (
"go/token"
"llvm.org/llgo/third_party/gotools/go/ssa"
)
func escapes(val ssa.Value, bb *ssa.BasicBlock, pending []ssa.Value) bool {
for _, p := range pending {
if val == p {
return false
}
}
for _, ref := range *val.Referrers() {
switch ref := ref.(type) {
case *ssa.Phi:
// We must consider the variable to have escaped if it is
// possible for the program to see more than one "version"
// of the variable at once, as this requires the program
// to use heap allocation for the multiple versions.
//
// I (pcc) think that this is only possible (without stores)
// in the case where a phi node that (directly or indirectly)
// refers to the allocation dominates the allocation.
if ref.Block().Dominates(bb) {
return true
}
if escapes(ref, bb, append(pending, val)) {
return true
}
case *ssa.BinOp, *ssa.ChangeType, *ssa.Convert, *ssa.ChangeInterface, *ssa.MakeInterface, *ssa.Slice, *ssa.FieldAddr, *ssa.IndexAddr, *ssa.TypeAssert, *ssa.Extract:
if escapes(ref.(ssa.Value), bb, append(pending, val)) {
return true
}
case *ssa.Range, *ssa.DebugRef:
continue
case *ssa.UnOp:
if ref.Op == token.MUL || ref.Op == token.ARROW {
continue
}
if escapes(ref, bb, append(pending, val)) {
return true
}
case *ssa.Store:
if val == ref.Val {
return true
}
case *ssa.Call:
if builtin, ok := ref.Call.Value.(*ssa.Builtin); ok {
switch builtin.Name() {
case "cap", "len", "copy", "ssa:wrapnilchk":
continue
case "append":
if ref.Call.Args[0] == val && escapes(ref, bb, append(pending, val)) {
return true
}
default:
return true
}
} else {
return true
}
default:
return true
}
}
return false
}
func LowerAllocsToStack(f *ssa.Function) {
pending := make([]ssa.Value, 0, 10)
for _, b := range f.Blocks {
for _, instr := range b.Instrs {
if alloc, ok := instr.(*ssa.Alloc); ok && alloc.Heap && !escapes(alloc, alloc.Block(), pending) {
alloc.Heap = false
f.Locals = append(f.Locals, alloc)
}
}
}
}
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