cmd/compile: internal compiler error: Value live at entry. It shouldn't be.

[LK4D4]

Please answer these questions before submitting your issue. Thanks!

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

go version devel +6e02750 Wed Oct 26 02:24:45 2016 +0000 linux/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH=""
GORACE=""
GOROOT="/home/moroz/go"
GOTOOLDIR="/home/moroz/go/pkg/tool/linux_amd64"
GCCGO="/usr/bin/gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build703362554=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

go get github.com/nsqio/nsq/apps/nsqd

What did you expect to see?

Compiled nsqd

What did you see instead?

# github.com/nsqio/go-nsq
src/github.com/nsqio/go-nsq/config.go:517: internal compiler error: Value live at entry. It shouldn't be. func coerce, node autotmp_499, value v1019

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
        /home/moroz/go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0xa47006, 0x40, 0xc4217b07b0, 0x3, 0x3)
        /home/moroz/go/src/cmd/compile/internal/gc/subr.go:165 +0x226
cmd/compile/internal/gc.(*ssaExport).Fatalf(0xd0f2f5, 0x33e, 0xa47006, 0x40, 0xc4217b07b0, 0x3, 0x3)
        /home/moroz/go/src/cmd/compile/internal/gc/ssa.go:4615 +0x5d
cmd/compile/internal/ssa.(*Config).Fatalf(0xc421454000, 0xc40000033e, 0xa47006, 0x40, 0xc4217b07b0, 0x3, 0x3)
        /home/moroz/go/src/cmd/compile/internal/ssa/config.go:319 +0x6e
cmd/compile/internal/gc.(*state).Fatalf(0xc42140ab40, 0xa47006, 0x40, 0xc4217b07b0, 0x3, 0x3)
        /home/moroz/go/src/cmd/compile/internal/gc/ssa.go:282 +0x83
cmd/compile/internal/gc.(*simplePhiState).insertPhis(0xc42124d528)
        /home/moroz/go/src/cmd/compile/internal/gc/phi.go:458 +0x284
cmd/compile/internal/gc.(*state).insertPhis(0xc42140ab40)
        /home/moroz/go/src/cmd/compile/internal/gc/phi.go:33 +0x172
cmd/compile/internal/gc.buildssa(0xc420e71830, 0x0)
        /home/moroz/go/src/cmd/compile/internal/gc/ssa.go:170 +0x901
cmd/compile/internal/gc.compile(0xc420e71830)
        /home/moroz/go/src/cmd/compile/internal/gc/pgen.go:359 +0x204
cmd/compile/internal/gc.funccompile(0xc420e71830)
        /home/moroz/go/src/cmd/compile/internal/gc/dcl.go:1282 +0xdc
cmd/compile/internal/gc.Main()
        /home/moroz/go/src/cmd/compile/internal/gc/main.go:469 +0x1eff
main.main()
        /home/moroz/go/src/cmd/compile/main.go:47 +0x15d

[dr2chase]

(Even) smaller reproducer:

package foo

import "fmt"

//go:noinline
func coerceStringer(v interface{}) (fmt.Stringer, error) {
    return &StringyThing{}, nil
}

type StringyThing struct {
}

func (*StringyThing) String() string {
    return "stringything"
}

func coerce(v interface{}, typ string) (interface{}, error) {
    var err error

    if typ == "Stringer" {
        v, err = coerceStringer(v)
    } else {
        v = nil
    }

    return v, err
}

[dr2chase]

Shorter reproducer above.
The badness seems to be entirely within walk.go, it constructs AST that looks like this (first mention of autotmp_2:

.   IF-body
.   .   BLOCK-init
.   .   .   AS l(21)
.   .   .   .   NAME-foo.autotmp_3 u(1) a(true) l(21) x(0) class(PAUTO) esc(N) tc(1) used(true) fmt.Stringer
.   .   .   .   NAME-foo.autotmp_2 u(1) a(true) l(21) x(0) class(PAUTO) esc(N) tc(1) used(true) fmt.Stringer

[dr2chase]

Problematic OAS node is constructed at this stack trace (common to both examples, involves OAS2FUNC going wrong in some special way):

#0  cmd/compile/internal/gc.nod (op=20 '\024', nleft=0xc4203d9560, nright=0xc4203d93b0, ~r3=0xc42035a2e0)
    at .../cmd/compile/internal/gc/subr.go:362
#1  0x0000000000547c4d in cmd/compile/internal/gc.walkexpr (n#150=0xc4203d94d0, init=0xc42036b310, ~r2=0x631013 <string.*+38683>)
    at .../cmd/compile/internal/gc/walk.go:1090
#2  0x0000000000553835 in cmd/compile/internal/gc.convas (n=0xc4203d9440, init=0xc42036b310, ~r2=0xc4203d93b0)
    at .../cmd/compile/internal/gc/walk.go:2340
#3  0x00000000005501a7 in cmd/compile/internal/gc.ascompatet (op=22 '\026', nl=..., nr=0xc420358360, fp=0, init=0xc42036b310, 
    ~r5= []*cmd/compile/internal/gc.Node) at .../cmd/compile/internal/gc/walk.go:1874
#4  0x000000000054371b in cmd/compile/internal/gc.walkexpr (n#150=0xc42035bcb0, init=0xc42036b310, ~r2=0x0)
    at .../cmd/compile/internal/gc/walk.go:823
#5  0x000000000054182a in cmd/compile/internal/gc.walkstmt (n#20=0xc42035bcb0, ~r1=0xc4203d8750)
    at .../cmd/compile/internal/gc/walk.go:192
#6  0x00000000005407c4 in cmd/compile/internal/gc.walkstmtlist (s= []*cmd/compile/internal/gc.Node = {...})
    at .../cmd/compile/internal/gc/walk.go:80

[bradfitz]

We just got this on an http2 trybot run:

https://storage.googleapis.com/go-build-log/1e6b12a2/linux-386_7f5f0646.log

linux-386 at 1e6b12a201e5fa7009510bb036367dfb0f5a6320 building net at 495e63a0f6f01eab21c56de7838a0139012a985e

# golang.org/x/net/http2
../../gopath/src/golang.org/x/net/http2/frame_test.go:859: internal compiler error: Value live at entry. It shouldn't be. func TestMetaFrameHeader, node autotmp_4023, value v1519

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /tmp/workdir/go/src/runtime/debug/stack.go:24 +0x64
cmd/compile/internal/gc.Fatalf(0x859805b, 0x40, 0x196125a0, 0x3, 0x3)
    /tmp/workdir/go/src/cmd/compile/internal/gc/subr.go:165 +0x1d2
cmd/compile/internal/gc.(*ssaExport).Fatalf(0x87f4115, 0x26d0, 0x859805b, 0x40, 0x196125a0, 0x3, 0x3)
    /tmp/workdir/go/src/cmd/compile/internal/gc/ssa.go:4615 +0x4b
cmd/compile/internal/ssa.(*Config).Fatalf(0x1a8da000, 0x26d0, 0x859805b, 0x40, 0x196125a0, 0x3, 0x3)
    /tmp/workdir/go/src/cmd/compile/internal/ssa/config.go:319 +0x57
cmd/compile/internal/gc.(*state).Fatalf(0x1af29500, 0x859805b, 0x40, 0x196125a0, 0x3, 0x3)
    /tmp/workdir/go/src/cmd/compile/internal/gc/ssa.go:282 +0x60
cmd/compile/internal/gc.(*simplePhiState).insertPhis(0x1ab49a78)
    /tmp/workdir/go/src/cmd/compile/internal/gc/phi.go:458 +0x20e
cmd/compile/internal/gc.(*state).insertPhis(0x1af29500)
    /tmp/workdir/go/src/cmd/compile/internal/gc/phi.go:33 +0x109
cmd/compile/internal/gc.buildssa(0x19a91e00, 0x0)
    /tmp/workdir/go/src/cmd/compile/internal/gc/ssa.go:170 +0x782
cmd/compile/internal/gc.compile(0x19a91e00)
    /tmp/workdir/go/src/cmd/compile/internal/gc/pgen.go:357 +0x1b9
cmd/compile/internal/gc.funccompile(0x19a91e00)
    /tmp/workdir/go/src/cmd/compile/internal/gc/dcl.go:1282 +0xd4
cmd/compile/internal/gc.Main()
    /tmp/workdir/go/src/cmd/compile/internal/gc/main.go:469 +0x1aa9
main.main()
    /tmp/workdir/go/src/cmd/compile/main.go:47 +0x137

ok      golang.org/x/net/bpf    0.465s
ok      golang.org/x/net/context    0.110s
ok      golang.org/x/net/context/ctxhttp    0.110s
?       golang.org/x/net/dict   [no test files]
ok      golang.org/x/net/html   0.089s
ok      golang.org/x/net/html/atom  0.005s
ok      golang.org/x/net/html/charset   0.006s
FAIL    golang.org/x/net/http2 [build failed]

/cc @tombergan

[bradfitz]

Actually trybot failure is unrelated; the net repo is all red on https://build.golang.org/ at tip already.

[josharian]

Bisecting.

[josharian]

Bisect says c78d072, which is re-enabling the convI2E optimization. Shall we revert the revert of the revert, @randall77?

[gopherbot]

CL https://golang.org/cl/32226 mentions this issue.

[dr2chase]

It's related to fncall, line 1834, which (incorrectly with I2E optimization) asserts that an I to E conversion requires a function call. Making the obvious fix clears the compile-time error and also passes all.bash, but generates bad code.

[gopherbot]

CL https://golang.org/cl/32184 mentions this issue.