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From: "alalaw01 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/67683] New: Missed vectorization: shifts of an induction variable
Date: Tue, 22 Sep 2015 17:21:00 -0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 6.0
X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67683

            Bug ID: 67683
           Summary: Missed vectorization: shifts of an induction variable
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alalaw01 at gcc dot gnu.org
            Blocks: 53947
  Target Milestone: ---

This testcase:

void test (unsigned char *data, int max)
{
  unsigned short val = 0xcdef;
  for(int i = 0; i < max; i++) { 
          data[i] = (unsigned char)(val & 0xff);
          val >>= 1; 
  }
}

does not vectorize on AArch64 or x86_64 at -O3. (I haven't yet looked at
whether it's a mid-end deficiency or both back-ends are missing patterns.)


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations