cmd/compile: inline multiplication corrupts an argument on arm

[frbrno]

What version of Go are you using (go version)?

go version go1.11.2 linux/amd64

Does this issue reproduce with the latest release?

YES

What operating system and processor architecture are you using (go env)?

go env Output

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/fred/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/fred/workspace/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build795351668=/tmp/go-build -gno-record-gcc-switches"

### What did you do?

package main
import (

"fmt"

)
func main() {

id := 1

a := float32(2.0)

b := float32(5.0)

testOut(id, a*b)

}
func testOut(id int, a float32) {

fmt.Println(id, a)

}
$ env GOOS=linux GOARCH=arm go build -o test.arm7 main.go
running on raspberry pi 3 Model:B V:2

Linux PiOne 4.14.79-1-ARCH #1 SMP Tue Nov 6 03:01:46 UTC 2018 armv7l GNU/Linux
$ ./test.arm7

What did you expect to see?

1 10

What did you see instead?

1073741824 10

When I do the multiplication outside the function call testOut() I get output (1 10).
Only happens when I do cross compilation.

When I cross compile and set GOARM=7, it works just fine.
env GOOS=linux GOARCH=arm GOARM=7 go build -o test.arm7 main.go

[mvdan]

@derfbn does this occur with Go 1.10 or previous Go versions?

[mvdan]

Tentatively marking as a release blocker for 1.12, until we're sure that this isn't important enough.

[frbrno]

go version go1.10.5 linux/amd64

go env Output

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/fred/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/fred/workspace/go"
GORACE=""
GOROOT="/home/fred/trash/gotest/go1.10.5/go"
GOTMPDIR=""
GOTOOLDIR="/home/fred/trash/gotest/go1.10.5/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build790837178=/tmp/go-build -gno-record-gcc-switches"

@mvdan does not occur on Go 1.10.5

[ianlancetaylor]

CC @randall77

[josharian]

Seems like a backport candidate. Let's wait to see what the diagnosis is.

[gopherbot]

Change https://golang.org/cl/148837 mentions this issue: cmd/compile/internal/gc: OMUL should be evaluated when using soft-float

[milanknezevic]

The issue can be reproduced on mips too.

[josharian]

@gopherbot please open a backport tracking issue for 1.11. This is a compiler correctness bug.

[gopherbot]

Backport issue(s) opened: #28694 (for 1.11).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[milanknezevic]

@josharian Could this also be backported to 1.10 because it affects mips softfloat support which is added in 1.10?