cmd/compile: fix x=x assignments
No point in doing anything for x=x assignments.
In addition, skipping these assignments prevents generating:
VARDEF x
COPY x -> x
which is bad because x is incorrectly considered
dead before the vardef.
Fixes #14904
Change-Id: I6817055ec20bcc34a9648617e0439505ee355f82
Reviewed-on: https://go-review.googlesource.com/21470
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 359f4b2..1c2e528 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -661,6 +661,17 @@
return
}
+ if n.Left == n.Right && n.Left.Op == ONAME {
+ // An x=x assignment. No point in doing anything
+ // here. In addition, skipping this assignment
+ // prevents generating:
+ // VARDEF x
+ // COPY x -> x
+ // which is bad because x is incorrectly considered
+ // dead before the vardef. See issue #14904.
+ return
+ }
+
var t *Type
if n.Right != nil {
t = n.Right.Type
