* [C++ PATCH] Fix -Wunused-but-set-* on RHS of x op= rhs if rhs has side-effects (PR c++/50158)
@ 2011-08-23 16:03 Jakub Jelinek
2011-08-23 16:31 ` Jason Merrill
0 siblings, 1 reply; 2+ messages in thread
From: Jakub Jelinek @ 2011-08-23 16:03 UTC (permalink / raw)
To: Jason Merrill; +Cc: gcc-patches
Hi!
The recent cp_build_modify_expr change broke the following testcase,
we now complain that b is set but not used. The problem is that
when rhs has side-effects, stabilize_expr returns a temporary (+ creates
a TARGET_EXPR), which means that mark_exp_read isn't actually called on the
original RHS expression.
Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?
2011-08-23 Jakub Jelinek <jakub@redhat.com>
PR c++/50158
* typeck.c (cp_build_modify_expr): Call mark_rvalue_use on rhs
if it has side-effects and needs to be preevaluated.
* g++.dg/warn/Wunused-var-16.C: New test.
--- gcc/cp/typeck.c.jj 2011-08-18 08:35:38.000000000 +0200
+++ gcc/cp/typeck.c 2011-08-23 14:36:42.000000000 +0200
@@ -6692,6 +6692,8 @@ cp_build_modify_expr (tree lhs, enum tre
side effect associated with any single compound assignment
operator. -- end note ] */
lhs = stabilize_reference (lhs);
+ if (TREE_SIDE_EFFECTS (rhs))
+ rhs = mark_rvalue_use (rhs);
rhs = stabilize_expr (rhs, &init);
newrhs = cp_build_binary_op (input_location,
modifycode, lhs, rhs,
--- gcc/testsuite/g++.dg/warn/Wunused-var-16.C.jj 2011-08-23 14:37:31.000000000 +0200
+++ gcc/testsuite/g++.dg/warn/Wunused-var-16.C 2011-08-23 14:37:19.000000000 +0200
@@ -0,0 +1,13 @@
+// PR c++/50158
+// { dg-do compile }
+// { dg-options "-Wunused" }
+
+int bar (int);
+
+int
+foo (int a)
+{
+ int b[] = { a, -a };
+ a += b[bar (a) < a];
+ return a;
+}
Jakub
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [C++ PATCH] Fix -Wunused-but-set-* on RHS of x op= rhs if rhs has side-effects (PR c++/50158)
2011-08-23 16:03 [C++ PATCH] Fix -Wunused-but-set-* on RHS of x op= rhs if rhs has side-effects (PR c++/50158) Jakub Jelinek
@ 2011-08-23 16:31 ` Jason Merrill
0 siblings, 0 replies; 2+ messages in thread
From: Jason Merrill @ 2011-08-23 16:31 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: gcc-patches
OK.
Jason
^ permalink raw reply [flat|nested] 2+ messages in thread
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2011-08-23 16:03 [C++ PATCH] Fix -Wunused-but-set-* on RHS of x op= rhs if rhs has side-effects (PR c++/50158) Jakub Jelinek
2011-08-23 16:31 ` Jason Merrill
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