Golang cmd/compile: duplicate instructions after rewrite func results

Go version

go version go1.26-devel_b10eb1d042 Mon Jul 28 17:39:26 2025 -0700 linux/amd64

Output of `go env` in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='0'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/kylin/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/kylin/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3413711938=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/kylin/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/kylin/go'
GOPRIVATE=''
GOPROXY='https://goproxy.cn,direct'
GOROOT='/home/kylin/go/src/googlesource.com/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/kylin/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/kylin/go/src/googlesource.com/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26-devel_b10eb1d042 Mon Jul 28 17:39:26 2025 -0700'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Disassemble the following function:

//go:noinline
func fn(a [2]int) (r [2]int) {
    return a
}

What did you see happen?

  0x4690e0              0f10442408              MOVUPS 0x8(SP), X0
  0x4690e5              0f11442418              MOVUPS X0, 0x18(SP)
  0x4690ea              0f10442408              MOVUPS 0x8(SP), X0
  0x4690ef              0f11442418              MOVUPS X0, 0x18(SP)
  0x4690f4              c3                      RET

What did you expect to see?

  0x4690e0              0f10442408              MOVUPS 0x8(SP), X0
  0x4690e5              0f11442418              MOVUPS X0, 0x18(SP)
  0x4690ea              c3                      RET

Comment From: gopherbot

Change https://go.dev/cl/691275 mentions this issue: cmd/compile: deduplicate instructions when rewrite func results