cmd/compile: coalesce adjacent writes to struct fields

[dsnet]

Go version

go1.22

Output of go env in your module/workspace:

GOARCH=amd64
GOOS=linux

What did you do?

Compile the following:

var sink A

func main() {
	sink = A{31, false, true, 12}
}

type A struct {
	a byte
	b bool
	c bool
	d int8
}

What did you see happen?

The compiler output something like:

0x0000 00000 (main.go:13)	MOVB	$31, main.sink(SB)
0x0007 00007 (main.go:13)	MOVB	$0, main.sink+1(SB)
0x000e 00014 (main.go:13)	MOVB	$1, main.sink+2(SB)
0x0015 00021 (main.go:13)	MOVB	$12, main.sink+3(SB)

What did you expect to see?

A single MOVL instruction.

[randall77]

Looks like just an oversight of the bool case in cmd/compile/internal/ssa/memcombine.go.
This patch fixes it, maybe:

--- a/src/cmd/compile/internal/ssa/memcombine.go
+++ b/src/cmd/compile/internal/ssa/memcombine.go
@@ -534,7 +534,7 @@ func combineStores(root *Value, n int64) bool {
        isConst := true
        for i := int64(0); i < n; i++ {
                switch a[i].store.Args[1].Op {
-               case OpConst32, OpConst16, OpConst8:
+               case OpConst32, OpConst16, OpConst8, OpConstBool:
                default:
                        isConst = false
                        break

[gopherbot]

Change https://go.dev/cl/573416 mentions this issue: cmd/compile: include constant bools in memcombine