go: cmd/compile, x/sync/errgroup: TestWithContext failing after devirtualization CL

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

$ go version
go version devel +fe70a3a0fd Thu Oct 29 21:46:54 2020 +0000 linux/amd64

Does this issue reproduce with the latest release?

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jake/.cache/go-build"
GOENV="/home/jake/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/jake/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jake/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/jake/sdk/gotip"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/jake/sdk/gotip/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/jake/zikaeroh/sync/go.mod"
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-build875916662=/tmp/go-build -gno-record-gcc-switches"
GOROOT/bin/go version: go version devel +fe70a3a0fd Thu Oct 29 21:46:54 2020 +0000 linux/amd64
GOROOT/bin/go tool compile -V: compile version devel +fe70a3a0fd Thu Oct 29 21:46:54 2020 +0000
uname -sr: Linux 5.9.1-zen2-1-zen
/usr/lib/libc.so.6: GNU C Library (GNU libc) release release version 2.32.
gdb --version: GNU gdb (GDB) 9.2

What did you do?

In the golang.org/x/sync/errgroup package, run go test.

What did you expect to see?

Passing tests.

What did you see instead?

--- FAIL: TestWithContext (0.00s)
panic: interface conversion: context.Context is *context.cancelCtx, not *context.emptyCtx [recovered]
	panic: interface conversion: context.Context is *context.cancelCtx, not *context.emptyCtx

goroutine 29 [running]:
testing.tRunner.func1.2(0x5b0e80, 0xc0000a4e70)
	/home/jake/sdk/gotip/src/testing/testing.go:1123 +0x332
testing.tRunner.func1(0xc000083080)
	/home/jake/sdk/gotip/src/testing/testing.go:1126 +0x4b6
panic(0x5b0e80, 0xc0000a4e70)
	/home/jake/sdk/gotip/src/runtime/panic.go:965 +0x1b9
golang.org/x/sync/errgroup_test.TestWithContext(0xc000083080)
	/home/jake/zikaeroh/sync/errgroup/errgroup_test.go:166 +0x652
testing.tRunner(0xc000083080, 0x5f4c88)
	/home/jake/sdk/gotip/src/testing/testing.go:1173 +0xef
created by testing.(*T).Run
	/home/jake/sdk/gotip/src/testing/testing.go:1218 +0x2b3
exit status 2
FAIL	golang.org/x/sync/errgroup	0.005s

https://build.golang.org/log/8759ffb3dd087325958f6d2d67773f3dd2f70cf2 https://build.golang.org/log/32b25547fddc3b46c217c9efffb9aa124df3766e

The dashboard shows this test consistently failing after the devirtualization CL, but this differs from #42279 as it affects runtime behavior.

cc @mdempsky

About this issue

Original URL
State: closed
Created 4 years ago
Comments: 15 (11 by maintainers)

Most upvoted comments

@kivikakk Thanks for the report! I was able to create a reproducer.

mdempsky on Dec 20, 2020

@cespare That’s a fair point. There’s certainly a trade off though: the more effort put into improving the early devirtualization code is effort taken away from moving escape analysis to SSA. The current early devirtualization pass is basically just a minor extension of the inlining / escape analysis improvements implemented for #41474

If you do see that practice developing, let us know and we can revisit whether there are more cases that we can handle without too much trouble.

mdempsky on Oct 30, 2020

Ah, I had no idea this was at the AST level where you couldn’t distinguish it. Clearly I’m not paying enough attention during your streams. 🙂

zikaeroh on Oct 30, 2020

See https://build.golang.org/?repo=golang.org%2Fx%2Fsync; the page is all red on tip.