cmd/compile: "truncation is not exact" ICE while compiling on ppc64le on QEMU

[SuperQ]

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

$ go version
go version go1.13 linux/ppc64le

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="ppc64le"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="ppc64le"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/peon/godev/go1.13/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/peon/godev/go1.13/go/pkg/tool/linux_ppc64le"
GCCGO="gccgo"
GOPPC64="power8"
AR="ar"
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 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build688207401=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Building prometheus/node_exporter fails.

Running a Debian 9 (stretch) ppc64le QEMU VM on Debian 10 (buster) amd64 host.
QEMU 3.1 and 4.1 both produce the same compile error.

GO111MODULE=on /home/peon/.buildkite-agent/builds/debian-9-4-0-ppc64le-build-prometheus-io-1/prometheus/node-exporter-5b1a191e7471d00deeee08ce305d1de245243936-2122-nYyt/bin/promu --config .promu.yml build --prefix /home/peon/.buildkite-agent/builds/debian-9-4-0-ppc64le-build-prometheus-io-1/prometheus/node-exporter-5b1a191e7471d00deeee08ce305d1de245243936-2122-nYyt/src/github.com/prometheus/node_exporter
  | >   node_exporter
  | # runtime
  | /home/peon/godev/go/src/runtime/runtime1.go:162:22: internal compiler error: 'check': panic during opt while compiling check:
  |  
  | truncate64Fto32F: truncation is not exact
  |  
  | goroutine 129 [running]:
  | cmd/compile/internal/ssa.Compile.func1(0xc0023aefa8, 0xc003c78f20)
  | /usr/local/go/src/cmd/compile/internal/ssa/compile.go:47 +0x9c
  | panic(0x8c63a0, 0xaf8740)
  | /usr/local/go/src/runtime/panic.go:679 +0x1bc
  | cmd/compile/internal/ssa.truncate64Fto32F(0xc7ffffffe0000000, 0xc000000852)
  | /usr/local/go/src/cmd/compile/internal/ssa/rewrite.go:444 +0xdc
  | cmd/compile/internal/ssa.auxTo32F(...)
  | /usr/local/go/src/cmd/compile/internal/ssa/rewrite.go:494
  | cmd/compile/internal/ssa.rewriteValuegeneric_OpEq32F_0(0xc00255ae58, 0xffffffffffffff01)
  | /usr/local/go/src/cmd/compile/internal/ssa/rewritegeneric.go:19739 +0x128
  | cmd/compile/internal/ssa.rewriteValuegeneric(0xc00255ae58, 0x0)
  | /usr/local/go/src/cmd/compile/internal/ssa/rewritegeneric.go:105 +0x18dc
  | cmd/compile/internal/ssa.applyRewrite(0xc003c78f20, 0x96be28, 0x96bea0)
  | /usr/local/go/src/cmd/compile/internal/ssa/rewrite.go:80 +0x538
  | cmd/compile/internal/ssa.opt(0xc003c78f20)
  | /usr/local/go/src/cmd/compile/internal/ssa/opt.go:9 +0x44
  | cmd/compile/internal/ssa.Compile(0xc003c78f20)
  | /usr/local/go/src/cmd/compile/internal/ssa/compile.go:92 +0x8a4
  | cmd/compile/internal/gc.buildssa(0xc0016f2840, 0x1, 0x0)
  | /usr/local/go/src/cmd/compile/internal/gc/ssa.go:289 +0x778
  | cmd/compile/internal/gc.compileSSA(0xc0016f2840, 0x1)
  | /usr/local/go/src/cmd/compile/internal/gc/pgen.go:298 +0x38
  | cmd/compile/internal/gc.compileFunctions.func2(0xc0026f4480, 0xc000501280, 0x1)
  | /usr/local/go/src/cmd/compile/internal/gc/pgen.go:363 +0x40
  | created by cmd/compile/internal/gc.compileFunctions
  | /usr/local/go/src/cmd/compile/internal/gc/pgen.go:361 +0x12c
  |  
  |  
  |  
  | Please file a bug report including a short program that triggers the error.
  | https://golang.org/issue/new
  | !! command failed: build -o /home/peon/.buildkite-agent/builds/debian-9-4-0-ppc64le-build-prometheus-io-1/prometheus/node-exporter-5b1a191e7471d00deeee08ce305d1de245243936-2122-nYyt/src/github.com/prometheus/node_exporter/node_exporter -ldflags -X github.com/prometheus/common/version.Version=0.18.1 -X github.com/prometheus/common/version.Revision=non-git -X github.com/prometheus/common/version.Branch=non-git -X github.com/prometheus/common/version.BuildUser=peon@debian-9-4-0-ppc64le.build.prometheus.io -X github.com/prometheus/common/version.BuildDate=20190906-08:37:12  -extldflags '-static' -mod=vendor -a -tags 'netgo static_build' github.com/prometheus/node_exporter: exit status 2

[ALTree]

Thanks for opening this. I've changed the title to clarify that this issue is only reproducible when emulating a ppc64le system on QEMU, since this a (possibly) relevant piece of information.

Feel free to speak up if I'm mistaken and this is also reproducible outside of QEMU.

[SuperQ]

Looks fine, thanks. I don't have any ppc64le hardware to reproduce on.

[laboger]

If you had a short reproducer program or better directions on how to get to the failure I could try it on ppc64le.

[SuperQ]

Just running make build on https://github.com/prometheus/node_exporter should do it.

[laboger]

node_exporter built successfully on all variations I tried: Debian 9 power8 and SLES power9. On the power8 I compiled using go from Go 1.13 and upstream on hardware, not QEMU.

This must have built successfully in Go 1.12?

[SuperQ]

@laboger Are you using a QEMU ppc64le guest VM? What version of QEMU?

[laboger]

I am not using QEMU. I only tried it on ppc64le hardware.

[SuperQ]

This issue is about QEMU.

[ALTree]

This issue is about QEMU.

I mean... we weren't sure. Now we (more or less) are. Thanks @laboger for testing on real hardware.

My question now is... is this a QEMU bug? It could be. After all, Go produces binaries that work on real ppc64le hardware.