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IF-conversion: teach the cost-model how to grade if-converted loops. 

llvm-svn: 169171
This commit is contained in:
Nadav Rotem 2012-12-03 22:46:31 +00:00
parent 78f6b03edc
commit fad16be973
1 changed files with 26 additions and 15 deletions
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41
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -321,6 +321,10 @@ public:
/// Returns the induction variables found in the loop.
InductionList *getInductionVars() { return &Inductions; }
/// Return true if the block BB needs to be predicated in order for the loop
/// to be vectorized.
bool blockNeedsPredication(BasicBlock *BB);
/// Check if this pointer is consecutive when vectorizing. This happens
/// when the last index of the GEP is the induction variable, or that the
/// pointer itself is an induction variable.
@ -354,10 +358,6 @@ private:
/// Collect the variables that need to stay uniform after vectorization.
void collectLoopUniforms();
/// Return true if the block BB needs to be predicated in order for the loop
/// to be vectorized.
bool blockNeedsPredication(BasicBlock *BB);
/// return true if all of the instructions in the block can be speculatively
/// executed.
bool blockCanBePredicated(BasicBlock *BB);
@ -2064,19 +2064,29 @@ LoopVectorizationCostModel::findBestVectorizationFactor(unsigned VF) {
}
unsigned LoopVectorizationCostModel::expectedCost(unsigned VF) {
// We can only estimate the cost of single basic block loops.
assert(1 == TheLoop->getNumBlocks() && "Too many blocks in loop");
BasicBlock *BB = TheLoop->getHeader();
unsigned Cost = 0;
// For each instruction in the old loop.
for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it != e; ++it) {
Instruction *Inst = it;
unsigned C = getInstructionCost(Inst, VF);
Cost += C;
DEBUG(dbgs() << "LV: Found an estimated cost of "<< C <<" for VF "<< VF <<
" For instruction: "<< *Inst << "\n");
// For each block.
for (Loop::block_iterator bb = TheLoop->block_begin(),
be = TheLoop->block_end(); bb != be; ++bb) {
unsigned BlockCost = 0;
BasicBlock *BB = *bb;
// 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;
Cost += BlockCost;
}
return Cost;
@ -2106,6 +2116,7 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
return VTTI->getCFInstrCost(I->getOpcode());
}
case Instruction::PHI:
//TODO: IF-converted IFs become selects.
return 0;
case Instruction::Add:
case Instruction::FAdd: