[llvm-bugs] [Bug 25085] New: SLPVectorizer misses a vectorization opportunity BBVectorizer doesn't

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25085

            Bug ID: 25085
           Summary: SLPVectorizer misses a vectorization opportunity
                    BBVectorizer doesn't
           Product: new-bugs
           Version: 3.7
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: pekka.jaaskelainen at tut.fi
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 15017
  --> https://llvm.org/bugs/attachment.cgi?id=15017&action=edit
LLVM IR without BBVectorizer

Attached are two .ll files from pocl kernel compiler after parallel region
formation.  I have marked "See here" in parallel-bbvectorize.ll to the first
place where I spotted a vectorized instruction which wasn't in
parallel-no-bbvectorize.ll. 

This is from NBody case from AMD SDK.  It causes a major performance regression
in case BBVectorizer is disabled.

See the pocl bug https://github.com/pocl/pocl/issues/251

Is this helpful in fixing the issue? Let me know if you want me to try and
patches.

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