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

[Jakub Jelinek <jakub at redhat dot com>]

On Thu, Nov 13, 2014 at 12:51:05PM -0800, Teresa Johnson wrote:
> On Thu, Nov 13, 2014 at 7:39 AM, Teresa Johnson <tejohnson@google.com> wrote:
> > On Thu, Nov 13, 2014 at 7:12 AM, Jakub Jelinek <jakub@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?

Ok, thanks.  But I have a comment regarding the test below:

> 2014-11-13  Teresa Johnson  <tejohnson@google.com>
> 
> gcc:
>         PR tree-optimization/63841
>         * tree-ssa-strlen.c (strlen_optimize_stmt): Ignore clobbers.
> 
> 2014-11-13  Teresa Johnson  <tejohnson@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());

Supposedly the printfs should have been removed and the #include <cstdio>
isn't needed then either.  No need to clutter the test output and log files.
On the other side, tests should abort (); or __builtin_abort (); on failure,
not just return non-zero.

> +
> +  return good != bad;
> +}

	Jakub