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cmd/compile: avoid an assignment of n.Type in walk

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In the future, walk will probably run concurrently
with SSA construction. It is possible for walk
to be walking a function node that is referred
to by another function undergoing SSA construction.
In that case, this particular assignment to n.Type
is race-y.

This assignment is also not necessary;
evconst does not change the type of n.
Both arguments to evconst must have the same type,
and at the end of evconst, n is replaced with n.Left.

Remove the assignment, and add a check to ensure
that its removal remains correct.

Updates #15756

Change-Id: Id95faaff42d5abd76be56445d1d3e285775de8bf
Reviewed-on: https://go-review.googlesource.com/38609
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2017-03-24 13:30:19 -07:00
parent 5e954047bc
commit 26be4b9113
1 changed files with 3 additions and 2 deletions
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5
src/cmd/compile/internal/gc/walk.go
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@ -1614,9 +1614,10 @@ opswitch:
// walk of y%1 may have replaced it by 0.
// Check whether n with its updated args is itself now a constant.
t := n.Type
evconst(n)
n.Type = t
if n.Type != t {
Fatalf("evconst changed Type: %v had type %v, now %v", n, t, n.Type)
}
if n.Op == OLITERAL {
n = typecheck(n, Erv)
}