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BBVectorize: Add a additional comment about the cost computation

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173580 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2013-01-26 16:49:04 +00:00
parent 7a8aba9064
commit ec5c3c2bd3
1 changed files with 6 additions and 0 deletions
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6
lib/Transforms/Vectorize/BBVectorize.cpp
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@ -994,6 +994,12 @@ namespace {
unsigned JCost = getInstrCost(J->getOpcode(), JT1, JT2);
Type *VT1 = getVecTypeForPair(IT1, JT1),
*VT2 = getVecTypeForPair(IT2, JT2);
// Note that this procedure is incorrect for insert and extract element
// instructions (because combining these often results in a shuffle),
// but this cost is ignored (because insert and extract element
// instructions are assigned a zero depth factor and are not really
// fused in general).
unsigned VCost = getInstrCost(I->getOpcode(), VT1, VT2);
if (VCost > ICost + JCost)