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From: "congh at google dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/60505] New: Warning caused by GCC vectorizer.
Date: Tue, 11 Mar 2014 22:01:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.9.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: congh at google dot com
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60505

            Bug ID: 60505
           Summary: Warning caused by GCC vectorizer.
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: congh at google dot com

The compilation on the code below fails with options "-Wall  -Werror -O2
-ftree-loop-vectorize". The reason is that the epilogue generated by the
vectorizer tries to access the memory outside of ovec[16] and the the vrp pass
emits the warning "array subscript is above array bounds" for the access to
ovec[i]. The vectorizer should not generate the epilogue for this loop.



void foo(char *in, char *out, int num)
{
 int i;
 unsigned char ovec[16] = {0};

 for(i=0; i < num ; ++i)
   out[i] = (ovec[i] = in[i]);
 out[num] = ovec[num/2];
}