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Give scalar if-converted blocks half the score because they are not always executed due to CF.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169223 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nadav Rotem 2012-12-04 07:11:52 +00:00
parent 6cb5719689
commit e6f2df9610
1 changed files with 5 additions and 5 deletions
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10
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -2159,17 +2159,17 @@ unsigned LoopVectorizationCostModel::expectedCost(unsigned VF) {
// For each instruction in the old loop.
for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it != e; ++it) {
unsigned C = getInstructionCost(it, VF);
Cost += C;
DEBUG(dbgs() << "LV: Found an estimated cost of "<< C <<" for VF " <<
VF << " For instruction: "<< *it << "\n");
}
// TODO: if-converted blocks can have a high-nest level. We need to
// calculate the loop nest level and multiply the cost accordingly.
if (Legal->blockNeedsPredication(*bb))
BlockCost *= 2;
// We assume that if-converted blocks have a 50% chance of being executed.
// When the code is scalar then some of the blocks are avoided due to CF.
// When the code is vectorized we execute all code paths.
if (Legal->blockNeedsPredication(*bb) && VF == 1)
BlockCost /= 2;
Cost += BlockCost;
}