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cmd/compile: internal compiler error: b3.Succs has duplicate block b3 #11593

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dvyukov opened this issue Jul 4, 2015 · 7 comments
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cmd/compile: internal compiler error: b3.Succs has duplicate block b3 #11593

dvyukov opened this issue Jul 4, 2015 · 7 comments
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Go1.6

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@dvyukov
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dvyukov commented Jul 4, 2015

on dev.ssa branch
go version devel +be2a3e2 Thu Jul 2 08:29:33 2015 +0000 linux/amd64

gc crashes on the following program:

package a
func f_ssa() {_:{_:_:}}
go.go:2: internal compiler error: b3.Succs has duplicate block b3
@dvyukov
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dvyukov commented Jul 4, 2015

@josharian @DanielMorsing

@DanielMorsing
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Are labels named _ valid go? It would seem like you can't use them ever, yet an unused label is invalid.

@dvyukov
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dvyukov commented Jul 4, 2015

@griesemer for spec question

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dvyukov commented Jul 4, 2015

Worth checking whether it crashes the same way with named labels.

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@DanielMorsing @dvyukov Labels named _ are valid. The _ identifier is a valid identifier everywhere a name is declared (as in a label declaration), but _ is never entered into a scope and thus is never defined/declared. Thus it doesn't "exist" and cannot be used or found as being unused. Very much like _ variables are valid and the compiler does not complain if they are not used.

@ianlancetaylor ianlancetaylor added this to the Go1.6 milestone Jul 11, 2015
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CL https://golang.org/cl/12093 mentions this issue.

gopherbot pushed a commit that referenced this issue Jul 12, 2015
@randall77
[dev.ssa] cmd/compile/internal/gc: handle _ label correctly
7e4c06d 
An empty label statement can just be ignored, as it cannot
be the target of any gotos.

Tests are already in test/fixedbugs/issue7538*.go

Fixes #11589
Fixes #11593

Change-Id: Iadcd639e7200ce16aa40fd7fa3eaf82522513e82
Reviewed-on: https://go-review.googlesource.com/12093
Reviewed-by: Daniel Morsing <daniel.morsing@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
@josharian
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Fixed by CL 12093.

@mikioh mikioh modified the milestones: Go1.5, Go1.6 Jul 23, 2015
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@josharian @mikioh @DanielMorsing @dvyukov @ianlancetaylor @randall77 @griesemer @gopherbot