cmd/compile/internal/ssa: occurred the wrong rewrite cycle detection

[orisano]

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

$ go version
go version go1.18rc1 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/orisano/Library/Caches/go-build"
GOENV="/Users/orisano/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/orisano/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/orisano/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/orisano/sdk/go1.18rc1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/orisano/sdk/go1.18rc1/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18rc1"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/orisano/tmp/repro/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/5s/d4b31rld7l7d1169gfk7cfl80000gn/T/go-build2915424394=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://go.dev/play/p/sw3yvtCuPYW?v=gotip

I tried to build this program with -gcflags='-d "ssa/opt/debug=2"'

What did you expect to see?

debug logs.

What did you see instead?

$ go build -gcflags='-d "ssa/opt/debug=2"'
# repro
opt: rewriting for f
rewriting v13 = Convert <unsafe.Pointer> v12 v1  ->  v13 = AddPtr <unsafe.Pointer> v7 v8
./a.go:6:56: internal compiler error: 'f': rewrite cycle detected

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

Note

I investigated the cause of this issue.
it only rewrote rewriting v13 = Convert <unsafe.Pointer> v12 v1 -> v13 = AddPtr <unsafe.Pointer> v7 v8 on the 1st step.
and then calculate the hash of this function, store it to the states.
on the 2nd step, it only proceeded to remove dead values.

go/src/cmd/compile/internal/ssa/rewrite.go

Lines 69 to 80 in baf61e4

	if v.Uses == 0 && v.removeable() {
	if v.Op != OpInvalid && deadcode == removeDeadValues {
	// Reset any values that are now unused, so that we decrement
	// the use count of all of its arguments.
	// Not quite a deadcode pass, because it does not handle cycles.
	// But it should help Uses==1 rules to fire.
	v.reset(OpInvalid)
	change = true
	}
	// No point rewriting values which aren't used.
	continue
	}

it calculated the hash of this function again, got the same result to trigger the rewrite cycle detected.

[cuonglm]

cc @josharian

[gopherbot]

Change https://go.dev/cl/392760 mentions this issue: cmd/compile: disable rewrite loop detector for deadcode-only changes

[randall77]

@gopherbot please open a backport issue for 1.18.

[gopherbot]

Backport issue(s) opened: #52366 (for 1.18).

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

[bo-er]

I had the same problem using GO version 1.18, after switching to Go 1.14 the problem is gone.

[randall77]

@bo-er This issue was fixed in 1.18.2.