cmd/compile: ppc64le: sign extension issue in go 1.21rc2

[eliben]

Reported by Jan Mercl on golang-dev@

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

$ go version
go version go1.21rc2 linux/ppc64le

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

$ uname -a
        Linux sqlite1 5.10.0-18-powerpc64le #1 SMP Debian 5.10.140-1 (2022-09-02) ppc64le GNU/Linux

What did you do?

Minimized reproducer at https://go.dev/play/p/ccmhhPkt0PI?v=gotip outputs

        55282
        55282

in the playground. Running the same code on linux/ppc64le:

        debian@sqlite1:~/tmp$ cat bug.go
        package main
       
        import (
                "fmt"
                "strconv"
        )
       
        func f(n int) int8 {
                return int8(n)
        }
       
        func main() {
                n, _ := strconv.Atoi("9")
                fmt.Println(int64(0xd7f2) & int64(f(-n)))
                fmt.Println(int64(0xd7f2) & int64(f(-9)))
        }

        debian@sqlite1:~/tmp$ go run bug.go
        242
        55282

[eliben]

cc @golang/ppc64

[gopherbot]

Change https://go.dev/cl/508775 mentions this issue: cmd/compile: On PPC64, preserve sign extension when masking

[pmur]

@gopherbot please consider a backport for 1.20 and 1.19, this is a compiler bug without a workaround.

[gopherbot]

Backport issue(s) opened: #61319 (for 1.19), #61320 (for 1.20).

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