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Hoist a nested loop into its own method.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144496 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2011-11-13 11:34:53 +00:00
parent df234353fb
commit 9fd4e056e4
1 changed files with 53 additions and 33 deletions
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86
lib/CodeGen/MachineBlockPlacement.cpp
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@ -208,6 +208,9 @@ class MachineBlockPlacement : public MachineFunctionPass {
MachineBasicBlock *LoopHeaderBB,
SmallVectorImpl<MachineBasicBlock *> &Blocks,
const BlockFilterSet *BlockFilter = 0);
MachineBasicBlock *selectBestSuccessor(MachineBasicBlock *BB,
BlockChain &Chain,
const BlockFilterSet *BlockFilter);
void buildChain(MachineBasicBlock *BB, BlockChain &Chain,
SmallVectorImpl<MachineBasicBlock *> &Blocks,
const BlockFilterSet *BlockFilter = 0);
@ -303,12 +306,60 @@ void MachineBlockPlacement::markChainSuccessors(
}
}
/// \brief Select the best successor for a block.
///
/// This looks across all successors of a particular block and attempts to
/// select the "best" one to be the layout successor. It only considers direct
/// successors which also pass the block filter. It will attempt to avoid
/// breaking CFG structure, but cave and break such structures in the case of
/// very hot successor edges.
///
/// \returns The best successor block found, or null if none are viable.
MachineBasicBlock *MachineBlockPlacement::selectBestSuccessor(
MachineBasicBlock *BB, BlockChain &Chain,
const BlockFilterSet *BlockFilter) {
const BranchProbability HotProb(4, 5); // 80%
MachineBasicBlock *BestSucc = 0;
BranchProbability BestProb = BranchProbability::getZero();
DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
SE = BB->succ_end();
SI != SE; ++SI) {
if (BlockFilter && !BlockFilter->count(*SI))
continue;
BlockChain &SuccChain = *BlockToChain[*SI];
if (&SuccChain == &Chain) {
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Already merged!\n");
continue;
}
BranchProbability SuccProb = MBPI->getEdgeProbability(BB, *SI);
// Only consider successors which are either "hot", or wouldn't violate
// any CFG constraints.
if (SuccChain.LoopPredecessors != 0 && SuccProb < HotProb) {
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> CFG conflict\n");
continue;
}
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb
<< " (prob)"
<< (SuccChain.LoopPredecessors != 0 ? " (CFG break)" : "")
<< "\n");
if (BestSucc && BestProb >= SuccProb)
continue;
BestSucc = *SI;
BestProb = SuccProb;
}
return BestSucc;
}
void MachineBlockPlacement::buildChain(
MachineBasicBlock *BB,
BlockChain &Chain,
SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
const BlockFilterSet *BlockFilter) {
const BranchProbability HotProb(4, 5); // 80%
assert(BB);
assert(BlockToChain[BB] == &Chain);
assert(*Chain.begin() == BB);
@ -322,38 +373,7 @@ void MachineBlockPlacement::buildChain(
// Look for the best viable successor if there is one to place immediately
// after this block.
MachineBasicBlock *BestSucc = 0;
BranchProbability BestProb = BranchProbability::getZero();
DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
SE = BB->succ_end();
SI != SE; ++SI) {
if (BlockFilter && !BlockFilter->count(*SI))
continue;
BlockChain &SuccChain = *BlockToChain[*SI];
if (&SuccChain == &Chain) {
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Already merged!\n");
continue;
}
BranchProbability SuccProb = MBPI->getEdgeProbability(BB, *SI);
// Only consider successors which are either "hot", or wouldn't violate
// any CFG constraints.
if (SuccChain.LoopPredecessors != 0 && SuccProb < HotProb) {
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> CFG conflict\n");
continue;
}
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb
<< " (prob)"
<< (SuccChain.LoopPredecessors != 0 ? " (CFG break)" : "")
<< "\n");
if (BestSucc && BestProb >= SuccProb)
continue;
BestSucc = *SI;
BestProb = SuccProb;
}
MachineBasicBlock *BestSucc = selectBestSuccessor(BB, Chain, BlockFilter);
// If an immediate successor isn't available, look for the best viable
// block among those we've identified as not violating the loop's CFG at