build: make.bash fails for GOOS=plan9 GOARCH=386

[dmitshur]

As reported by the plan9-386-0intro builder and legacy misc-compile-plan9-386 trybot, the plan9/386 port fails to bootstrap:

gotip $ git rev-parse HEAD
e7bf9959fd9ea649e1513cef16f91f81b136045f
gotip $ cd src                           
src $ GOOS=plan9 GOARCH=386 ./make.bash
Building Go cmd/dist using /usr/local/go. (go1.22.3 darwin/arm64)
Building Go toolchain1 using /usr/local/go.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building commands for host, darwin/arm64.
Building packages and commands for target, plan9/386.
go tool dist: unexpected stale targets reported by /Users/gopher/gotip/pkg/tool/darwin_arm64/go_bootstrap list -gcflags="" -ldflags="" for [cmd/asm cmd/cgo cmd/compile cmd/link cmd/preprofile] (consider rerunning with GOMAXPROCS=1 GODEBUG=gocachehash=1):
	STALE cmd/compile: not installed but available in build cache

src $ echo $?
2

Also see https://build.golang.org/log/f237bed35a32f61819468d4cfd1b28946cb3e4d1 and https://storage.googleapis.com/go-build-log/ecc40e66/misc-compile-plan9-386_f210191c.log.

This doesn't happen for other ports. It also doesn't happen for other GOARCH values of GOOS=plan9 like plan9/amd64 and plan9/arm, only for plan9/386.

CC @golang/plan9.

[0intro]

It looks like it's broken since CL 577935.

CC @millerresearch

[0intro]

This change works around the issue:

--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -7316,7 +7316,7 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
 		//   good for amd64
 		//   not helpful for Apple Silicon
 		//
-		case "amd64", "386":
+		case "amd64":
 			// Align to 64 if 31 or fewer bytes remain in a cache line
 			// benchmarks a little better than always aligning, and also
 			// adds slightly less to the (PGO-compiled) binary size.

The question is now why it doesn't work for plan9/386?

[gopherbot]

Change https://go.dev/cl/586775 mentions this issue: dashboard: remove misc-compile-plan9-386

[gopherbot]

Change https://go.dev/cl/586835 mentions this issue: cmd/compile: disable AlignHot on plan9/386

[gopherbot]

Change https://go.dev/cl/589656 mentions this issue: dashboard: restore misc-compile-plan9-386

[dmitshur]

The bootstrap failure is now resolved via CL 586835, which is what the original report was about. Perhaps it would work well to close this issue and open a separate one to investigate why AlignHot breaks plan9/386 bootstrapping, and possibly track re-enabling it.