[go] cmd/compile: teach deadstore about moves
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Keith Randall (Gerrit)
Apr 28, 2026, 5:49:00 PM (11 hours ago) Apr 28
to David Chase, Cuong Manh Le, goph...@pubsubhelper.golang.org, Milind Chabbi, Keith Randall, golang-co...@googlegroups.com
Attention needed from Cuong Manh Le and David Chase
Keith Randall has uploaded the change for review![]( "Open in Gerrit")
Keith Randall would like David Chase and Cuong Manh Le to review this change.
Commit message
cmd/compile: teach deadstore about moves
Moves that read from read-only memory can't be reading the results
of a previous store. These are often generated by constant struct literals.
Moves whose results aren't needed because that memory is immediately
overwritten, are not needed.
Saves a few bytes of generated code (~<0.1%).
Change-Id: I8dab6d1b9c066d6b623eae8b8fe31a51dd3de006
Change diff
diff --git a/src/cmd/compile/internal/ssa/deadstore.go b/src/cmd/compile/internal/ssa/deadstore.go
index 17a0809..fc796d1 100644
--- a/src/cmd/compile/internal/ssa/deadstore.go
+++ b/src/cmd/compile/internal/ssa/deadstore.go
@@ -50,7 +50,18 @@
for _, a := range v.Args {
if a.Block == b && a.Type.IsMemory() {
storeUse.add(a.ID)
- if v.Op != OpStore && v.Op != OpZero && v.Op != OpVarDef {
+ switch v.Op {
+ case OpStore, OpZero, OpVarDef:
+ // These ops never read from their memory input.
+ case OpMove:
+ // This op reads from its memory argument, but
+ // we can treat it as not doing so if we know
+ // the read is from read-only memory.
+ if v.Args[1].Op == OpAddr && symIsRO(auxToSym(v.Args[1].Aux)) {
+ break
+ }
+ fallthrough
+ default:
// CALL, DUFFCOPY, etc. are both
// reads and writes.
loadUse.add(a.ID)
@@ -111,7 +122,7 @@
shadowed.clear()
shadowedRanges = shadowedRanges[:0]
}
- if v.Op == OpStore || v.Op == OpZero {
+ if v.Op == OpStore || v.Op == OpZero || v.Op == OpMove {
ptr := v.Args[0]
var off int64
for ptr.Op == OpOffPtr { // Walk to base pointer
@@ -119,7 +130,7 @@
ptr = ptr.Args[0]
}
var sz int64
- if v.Op == OpStore {
+ if v.Op == OpStore || v.Op == OpMove {
sz = v.Aux.(*types.Type).Size()
} else { // OpZero
sz = v.AuxInt
@@ -137,13 +148,14 @@
}
if si != nil && si.contains(off, off+sz) {
- // Modify the store/zero into a copy of the memory state,
+ // Modify the store/zero/move into a copy of the memory state,
// effectively eliding the store operation.
- if v.Op == OpStore {
- // store addr value mem
+ if v.Op == OpStore || v.Op == OpMove {
+ // Store addr value mem
+ // or Move dst src mem
v.SetArgs1(v.Args[2])
} else {
- // zero addr mem
+ // Zero addr mem
v.SetArgs1(v.Args[1])
}
v.Aux = nil
diff --git a/test/codegen/deadstore.go b/test/codegen/deadstore.go
new file mode 100644
index 0000000..fcea34f
--- /dev/null
+++ b/test/codegen/deadstore.go
@@ -0,0 +1,29 @@
+// asmcheck
+
+// Copyright 2026 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 codegen
+
+type S struct {
+ a, b, c, d, e int
+}
+
+func f1(s *S) {
+ // amd64:-`MOVUPS`
+ // arm64:-`STP` - `MOVD`
+ *s = S{}
+ *s = S{a: 3, b: 4, c: 5, d: 6, e: 7}
+}
+
+func f2(s *S) {
+ // amd64:-`MOVUPS`
+ // arm64:-`MOVD` -`FSTPQ`
+ *s = S{a: 1, b: 2, c: 3, d: 4, e: 5}
+ s.a = 3
+ s.b = 4
+ s.c = 5
+ s.d = 6
+ s.e = 7
+}
Change information
Files:
- M src/cmd/compile/internal/ssa/deadstore.go
- A test/codegen/deadstore.go
Change size: M
Delta: 2 files changed, 48 insertions(+), 7 deletions(-)
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- David Chase
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Cuong Manh Le (Gerrit)
Apr 28, 2026, 8:57:25 PM (8 hours ago) Apr 28
to Keith Randall, goph...@pubsubhelper.golang.org, golang...@luci-project-accounts.iam.gserviceaccount.com, David Chase, Milind Chabbi, golang-co...@googlegroups.com
Attention needed from David Chase and Keith Randall
Cuong Manh Le added 1 comment![]( "Open in Gerrit")
File test/codegen/deadstore.go
Line 15, Patchset 1 (Latest):
// arm64:-`STP` - `MOVD`Cuong Manh Le . unresolved
Should be no space here, I guess.
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Keith Randall (Gerrit)
Apr 28, 2026, 9:08:58 PM (8 hours ago) Apr 28
to Keith Randall, goph...@pubsubhelper.golang.org, golang...@luci-project-accounts.iam.gserviceaccount.com, David Chase, Cuong Manh Le, Milind Chabbi, golang-co...@googlegroups.com
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Keith Randall added 1 comment![]( "Open in Gerrit")
File test/codegen/deadstore.go
Line 15, Patchset 1 (Latest):
// arm64:-`STP` - `MOVD`Cuong Manh Le . resolved
Should be no space here, I guess.
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Keith Randall (Gerrit)
Apr 28, 2026, 9:09:24 PM (8 hours ago) Apr 28
to Keith Randall, goph...@pubsubhelper.golang.org, golang-co...@googlegroups.com
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Keith Randall uploaded new patchset![]( "Open in Gerrit")
Keith Randall uploaded patch set #2 to this change.
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Cuong Manh Le (Gerrit)
Apr 28, 2026, 9:10:01 PM (8 hours ago) Apr 28
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Cuong Manh Le voted Code-Review+2![]( "Open in Gerrit")
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Keith Randall (Gerrit)
Apr 28, 2026, 9:20:35 PM (8 hours ago) Apr 28
to Keith Randall, goph...@pubsubhelper.golang.org, Cuong Manh Le, golang...@luci-project-accounts.iam.gserviceaccount.com, David Chase, Milind Chabbi, golang-co...@googlegroups.com
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Keith Randall voted Code-Review+1![]( "Open in Gerrit")
| Code-Review | +1 |
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