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Date: Sun, 25 Nov 2007 10:26:00 -0000
Subject: [Bug tree-optimization/34223]  New: missed optimization - complete unrolling pass before the vectorizer
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From: "eres at il dot ibm dot com" <gcc-bugzilla@gcc.gnu.org>
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Consider the following test compiled with r130351 on ppc64-linux:

#define M 10
#define N 3

void
foo (int n, int *ub, int *uc)
{
  int i, j, tmp1;

  for (i = 0; i < n; i++)
    {
      tmp1 = 0;
      for (j = 0; j < M; j++)
        {
          tmp1 += uc[i] * ((int)(j << N) / M);
        }
      ub[i] = tmp1;
    }
}

Here is a snippet from the vectorizer dump:

c.c:12: note: not vectorized: relevant stmt not supported: D.1652_13 = j_29 <<
3
c.c:12: note: bad operation or unsupported loop bound.

[Adding a complete unrolling + ccp passes before the vectorizer can help to
vectorize the outer loop]


-- 
           Summary: missed optimization - complete unrolling pass before the
                    vectorizer
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eres at il dot ibm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34223