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

[joneskoo]

internal compiler error: Value live at entry. It shouldn't be. func (*colorizer).Write, node line, value v81

I got this error in VS Code and here I've minimized it somewhat.

I'm using go version go1.8 darwin/amd64 but this problem can be reproduced at play.golang.org.

https://play.golang.org/p/kN2xSXSzH5

If you run it, you get:

tmp/sandbox374087104/main.go:26: internal compiler error: Value live at entry. It shouldn't be. func (*colorizer).Write, node line, value v81

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
	/usr/local/go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0xacd433, 0x40, 0xc4204071a0, 0x3, 0x3)
	/usr/local/go/src/cmd/compile/internal/gc/subr.go:167 +0x226
cmd/compile/internal/gc.(*ssaExport).Fatalf(0xdcb195, 0x1a, 0xacd433, 0x40, 0xc4204071a0, 0x3, 0x3)
	/usr/local/go/src/cmd/compile/internal/gc/ssa.go:4979 +0x5d
cmd/compile/internal/ssa.(*Config).Fatalf(0xc4203ae000, 0xc40000001a, 0xacd433, 0x40, 0xc4204071a0, 0x3, 0x3)
	/usr/local/go/src/cmd/compile/internal/ssa/config.go:343 +0x6e
cmd/compile/internal/gc.(*state).Fatalf(0xc42031e4b0, 0xacd433, 0x40, 0xc4204071a0, 0x3, 0x3)
	/usr/local/go/src/cmd/compile/internal/gc/ssa.go:286 +0x83
cmd/compile/internal/gc.(*simplePhiState).insertPhis(0xc4203a74b0)
	/usr/local/go/src/cmd/compile/internal/gc/phi.go:458 +0x2c5
cmd/compile/internal/gc.(*state).insertPhis(0xc42031e4b0)
	/usr/local/go/src/cmd/compile/internal/gc/phi.go:33 +0x172
cmd/compile/internal/gc.buildssa(0xc420397e60, 0x0)
	/usr/local/go/src/cmd/compile/internal/gc/ssa.go:174 +0x8ee
cmd/compile/internal/gc.compile(0xc420397e60)
	/usr/local/go/src/cmd/compile/internal/gc/pgen.go:362 +0x204
cmd/compile/internal/gc.funccompile(0xc420397e60)
	/usr/local/go/src/cmd/compile/internal/gc/dcl.go:1292 +0xdc
cmd/compile/internal/gc.Main()
	/usr/local/go/src/cmd/compile/internal/gc/main.go:464 +0x1f08
main.main()
	/usr/local/go/src/cmd/compile/main.go:50 +0xfe

I think this looks like an internal error that shouldn't be due to my incorrect code (which may or may not have been the original trigger).

[joneskoo]

https://play.golang.org/p/qFArI-VoUn further minimized.

[ALTree]

Thanks for the report.

This issue is still present at tip, and it was introduced in CL 27203 (cmd/compile/internal/gc: enable new parser by default).

cc @mdempsky @griesemer

[joneskoo]

Looking at the language spec, https://golang.org/ref/spec#ForClause I think this is an error because

The init statement may be a short variable declaration, but the post statement must not.

So it should raise an error about bad syntax, not internal error.

[zigo101]

btw, why define PostStmt as SimpleStmt https://golang.org/ref/spec#PostStmt

PostStmt = SimpleStmt .

instead of

PostStmt = EmptyStmt | ExpressionStmt | SendStmt | IncDecStmt | Assignment .

?

[griesemer]

@golang101 Because it's easier to see that similarities between Init and Post statements than if the one difference was emphasized in the grammar explicitly.

[griesemer]

@ALTree Thanks for tracking this down. It appears that I missed an extra test that was present in the old code:

if post != nil && post.Colas {
        yyerror("cannot declare in the for-increment")
}

Fix forthcoming.

[gopherbot]

CL https://golang.org/cl/38375 mentions this issue.