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cmd/compile/internal/escape: add debug hash for literal allocation optimizations

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Several CLs earlier in this stack added optimizations to reduce
user allocations by recognizing and taking advantage of literals,
including CL 649555, CL 649079, and CL 649035.

This CL adds debug hashing of those changes, which enables use of the
bisect tool, such as 'bisect -compile=literalalloc go test -run=Foo'.
This also allows these optimizations to be manually disabled via
'-gcflags=all=-d=literalallochash=n'.

Updates #71359

Change-Id: I854f7742a6efa5b17d914932d61a32b2297f0c88
Reviewed-on: https://go-review.googlesource.com/c/go/+/675415
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
thepudds 2025-06-28 16:53:37 -04:00 • committed by t hepudds
parent 479b51ee1f
commit e46d586edd
5 changed files with 20 additions and 2 deletions
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1
src/cmd/compile/internal/base/debug.go
View file

@ -40,6 +40,7 @@ type DebugFlags struct {
InlFuncsWithClosures int `help:"allow functions with closures to be inlined" concurrent:"ok"`
InlStaticInit int `help:"allow static initialization of inlined calls" concurrent:"ok"`
Libfuzzer int `help:"enable coverage instrumentation for libfuzzer"`
LiteralAllocHash string `help:"hash value for use in debugging literal allocation optimizations" concurrent:"ok"`
LoopVar int `help:"shared (0, default), 1 (private loop variables), 2, private + log"`
LoopVarHash string `help:"for debugging changes in loop behavior. Overrides experiment and loopvar flag."`
LocationLists int `help:"print information about DWARF location list creation"`

4
src/cmd/compile/internal/base/flag.go
View file

@ -268,6 +268,10 @@ func ParseFlags() {
if Debug.PGOHash != "" {
PGOHash = NewHashDebug("pgohash", Debug.PGOHash, nil)
}
if Debug.LiteralAllocHash != "" {
LiteralAllocHash = NewHashDebug("literalalloc", Debug.LiteralAllocHash, nil)
}
if Debug.MergeLocalsHash != "" {
MergeLocalsHash = NewHashDebug("mergelocals", Debug.MergeLocalsHash, nil)
}

1
src/cmd/compile/internal/base/hashdebug.go
View file

@ -56,6 +56,7 @@ var hashDebug *HashDebug
var FmaHash *HashDebug // for debugging fused-multiply-add floating point changes
var LoopVarHash *HashDebug // for debugging shared/private loop variable changes
var PGOHash *HashDebug // for debugging PGO optimization decisions
var LiteralAllocHash *HashDebug // for debugging literal allocation optimizations
var MergeLocalsHash *HashDebug // for debugging local stack slot merging changes
var VariableMakeHash *HashDebug // for debugging variable-sized make optimizations

8
src/cmd/compile/internal/escape/escape.go
View file

@ -567,6 +567,10 @@ func (b *batch) rewriteWithLiterals(n ir.Node, fn *ir.Func) {
base.Fatalf("unexpected BasicLit Kind")
}
if constant.Compare(lit.Val(), token.GEQ, constant.MakeInt64(0)) {
if !base.LiteralAllocHash.MatchPos(n.Pos(), nil) {
// De-selected by literal alloc optimizations debug hash.
return
}
// Preserve any side effects of the original expression, then replace it.
assignTemp(*r, n.PtrInit())
*r = lit
@ -580,6 +584,10 @@ func (b *batch) rewriteWithLiterals(n ir.Node, fn *ir.Func) {
if conv.X.Op() != ir.OLITERAL && !conv.X.Type().IsInterface() {
v := ro.StaticValue(conv.X)
if v != nil && v.Op() == ir.OLITERAL && ir.ValidTypeForConst(conv.X.Type(), v.Val()) {
if !base.LiteralAllocHash.MatchPos(n.Pos(), nil) {
// De-selected by literal alloc optimizations debug hash.
return
}
if base.Debug.EscapeDebug >= 3 {
base.WarnfAt(n.Pos(), "rewriting OCONVIFACE value from %v (%v) to %v (%v)", conv.X, conv.X.Type(), v, v.Type())
}

8
src/cmd/compile/internal/walk/order.go
View file

@ -246,14 +246,18 @@ func (o *orderState) addrTemp(n ir.Node) ir.Node {
if v == nil {
v = n
}
optEnabled := func(n ir.Node) bool {
// Do this optimization only when enabled for this node.
return base.LiteralAllocHash.MatchPos(n.Pos(), nil)
}
if (v.Op() == ir.OSTRUCTLIT || v.Op() == ir.OARRAYLIT) && !base.Ctxt.IsFIPS() {
if ir.IsZero(v) && 0 < v.Type().Size() && v.Type().Size() <= abi.ZeroValSize {
if ir.IsZero(v) && 0 < v.Type().Size() && v.Type().Size() <= abi.ZeroValSize && optEnabled(n) {
// This zero value can be represented by the read-only zeroVal.
zeroVal := ir.NewLinksymExpr(v.Pos(), ir.Syms.ZeroVal, n.Type())
vstat := typecheck.Expr(zeroVal).(*ir.LinksymOffsetExpr)
return vstat
}
if isStaticCompositeLiteral(v) {
if isStaticCompositeLiteral(v) && optEnabled(n) {
// v can be directly represented in the read-only data section.
lit := v.(*ir.CompLitExpr)
vstat := readonlystaticname(n.Type())