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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/63185] New: Improve DSE with branches
Date: Fri, 05 Sep 2014 10:51:00 -0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 5.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: glisse at gcc dot gnu.org
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63185

            Bug ID: 63185
           Summary: Improve DSE with branches
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org

#include <stdlib.h>
#include <string.h>
void g();
void f(int n){
  char*p=malloc(1024);
  memset(p,8,1024);
  if(n)g();
}

We do not manage to remove the dead store (memset) because there is a PHI that
doesn't post-dominate the statement.