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