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LoopVectorize: External uses must use the last value in a reduction cycle

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Otherwise, we don't perform operations that would have been performed on
the scalar version.

Fixes PR17498.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192133 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer
2013-10-07 21:05:43 +00:00
parent 42be15fcbe
commit 1ee3c0008b
2 changed files with 33 additions and 0 deletions
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6
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -4015,6 +4015,12 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
if (ExitInstruction != 0 || Cur == Phi)
return false;
// The instruction used by an outside user must be the last instruction
// before we feed back to the reduction phi. Otherwise, we loose VF-1
// operations on the value.
if (std::find(Phi->op_begin(), Phi->op_end(), Cur) == Phi->op_end())
return false;
ExitInstruction = Cur;
continue;
}