Re: [PATCH] Fix PR/63841: empty constructor doesn't zero-initialize

[Teresa Johnson]

On Thu, Nov 13, 2014 at 7:39 AM, Teresa Johnson <tejohn...@google.com> wrote:
> On Thu, Nov 13, 2014 at 7:12 AM, Jakub Jelinek <ja...@redhat.com> wrote:
>> And for release branches I'd really prefer tree-ssa-strlen.c change.
>
> Ok, I started testing the initializer_zerop change on the 4_9 branch,
> will also test the strlen fix and send that patch for review here when
> it completes.

Here is the more conservative patch for 4_9. Bootstrapped and tested
on x86_64-unknown-linux-gnu. Ok for gcc-4_9 branch?

Thanks,
Teresa

2014-11-13  Teresa Johnson  <tejohn...@google.com>

gcc:
        PR tree-optimization/63841
        * tree-ssa-strlen.c (strlen_optimize_stmt): Ignore clobbers.

2014-11-13  Teresa Johnson  <tejohn...@google.com>

gcc/testsuite:
        PR tree-optimization/63841
        * testsuite/g++.dg/tree-ssa/pr63841.C: New test.

Index: tree-ssa-strlen.c
===================================================================
--- tree-ssa-strlen.c   (revision 217503)
+++ tree-ssa-strlen.c   (working copy)
@@ -1856,7 +1856,7 @@ strlen_optimize_stmt (gimple_stmt_iterator *gsi)
            break;
          }
     }
-  else if (is_gimple_assign (stmt))
+  else if (is_gimple_assign (stmt) && !gimple_clobber_p (stmt))
     {
       tree lhs = gimple_assign_lhs (stmt);

Index: testsuite/g++.dg/tree-ssa/pr63841.C
===================================================================
--- testsuite/g++.dg/tree-ssa/pr63841.C (revision 0)
+++ testsuite/g++.dg/tree-ssa/pr63841.C (working copy)
@@ -0,0 +1,38 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#include <cstdio>
+#include <string>
+
+std::string __attribute__ ((noinline)) comp_test_write() {
+  std::string data;
+
+  for (int i = 0; i < 2; ++i) {
+    char b = 1 >> (i * 8);
+    data.append(&b, 1);
+  }
+
+  return data;
+}
+
+std::string __attribute__ ((noinline)) comp_test_write_good() {
+  std::string data;
+
+  char b;
+  for (int i = 0; i < 2; ++i) {
+    b = 1 >> (i * 8);
+    data.append(&b, 1);
+  }
+
+  return data;
+}
+
+int main() {
+  std::string good = comp_test_write_good();
+  printf("expected: %hx\n", *(short*)good.c_str());
+
+  std::string bad = comp_test_write();
+  printf("got: %hx\n", *(short*)bad.c_str());
+
+  return good != bad;
+}



-- 
Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413