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-rw-r--r--lib/CodeGen/MachineBlockPlacement.cpp81
1 files changed, 60 insertions, 21 deletions
diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp
index de813a378e..ca17ad07e4 100644
--- a/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/lib/CodeGen/MachineBlockPlacement.cpp
@@ -206,7 +206,7 @@ class MachineBlockPlacement : public MachineFunctionPass {
void markChainSuccessors(BlockChain &Chain,
MachineBasicBlock *LoopHeaderBB,
- SmallVectorImpl<MachineBasicBlock *> &Blocks,
+ SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
const BlockFilterSet *BlockFilter = 0);
MachineBasicBlock *selectBestSuccessor(MachineBasicBlock *BB,
BlockChain &Chain,
@@ -214,8 +214,12 @@ class MachineBlockPlacement : public MachineFunctionPass {
MachineBasicBlock *selectBestCandidateBlock(
BlockChain &Chain, SmallVectorImpl<MachineBasicBlock *> &WorkList,
const BlockFilterSet *BlockFilter);
+ MachineBasicBlock *getFirstUnplacedBlock(const BlockChain &PlacedChain,
+ ArrayRef<MachineBasicBlock *> Blocks,
+ unsigned &PrevUnplacedBlockIdx);
void buildChain(MachineBasicBlock *BB, BlockChain &Chain,
- SmallVectorImpl<MachineBasicBlock *> &Blocks,
+ ArrayRef<MachineBasicBlock *> Blocks,
+ SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
const BlockFilterSet *BlockFilter = 0);
void buildLoopChains(MachineFunction &F, MachineLoop &L);
void buildCFGChains(MachineFunction &F);
@@ -403,17 +407,41 @@ MachineBasicBlock *MachineBlockPlacement::selectBestCandidateBlock(
return BestBlock;
}
+/// \brief Retrieve the first unplaced basic block.
+///
+/// This routine is called when we are unable to use the CFG to walk through
+/// all of the basic blocks and form a chain due to unnatural loops in the CFG.
+/// We walk through the sequence of blocks, starting from the
+/// LastUnplacedBlockIdx. We update this index to avoid re-scanning the entire
+/// sequence on repeated calls to this routine.
+MachineBasicBlock *MachineBlockPlacement::getFirstUnplacedBlock(
+ const BlockChain &PlacedChain,
+ ArrayRef<MachineBasicBlock *> Blocks,
+ unsigned &PrevUnplacedBlockIdx) {
+ for (unsigned i = PrevUnplacedBlockIdx, e = Blocks.size(); i != e; ++i) {
+ MachineBasicBlock *BB = Blocks[i];
+ if (BlockToChain[BB] != &PlacedChain) {
+ PrevUnplacedBlockIdx = i;
+ return BB;
+ }
+ }
+ return 0;
+}
+
void MachineBlockPlacement::buildChain(
MachineBasicBlock *BB,
BlockChain &Chain,
+ ArrayRef<MachineBasicBlock *> Blocks,
SmallVectorImpl<MachineBasicBlock *> &BlockWorkList,
const BlockFilterSet *BlockFilter) {
assert(BB);
assert(BlockToChain[BB] == &Chain);
assert(*Chain.begin() == BB);
+ SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
+ unsigned PrevUnplacedBlockIdx = 0;
+
MachineBasicBlock *LoopHeaderBB = BB;
markChainSuccessors(Chain, LoopHeaderBB, BlockWorkList, BlockFilter);
- SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
BB = *llvm::prior(Chain.end());
for (;;) {
assert(BB);
@@ -429,10 +457,12 @@ void MachineBlockPlacement::buildChain(
Cond.clear();
MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch.
if (TII->AnalyzeBranch(*BB, TBB, FBB, Cond) && BB->canFallThrough()) {
- MachineFunction::iterator I(BB);
- assert(llvm::next(I) != BB->getParent()->end() &&
- "The final block in the function can fallthrough!");
- BestSucc = llvm::next(I);
+ MachineFunction::iterator I(BB), NextI(llvm::next(I));
+ // Ensure that the layout successor is a viable block, as we know that
+ // fallthrough is a possibility.
+ assert(NextI != BB->getParent()->end());
+ assert(!BlockFilter || BlockFilter->count(NextI));
+ BestSucc = NextI;
}
// Otherwise, look for the best viable successor if there is one to place
@@ -440,13 +470,6 @@ void MachineBlockPlacement::buildChain(
if (!BestSucc)
BestSucc = selectBestSuccessor(BB, Chain, BlockFilter);
- if (BestSucc) {
- // Zero out LoopPredecessors for the successor we're about to merge. We
- // do this here instead of during the merge to catch cases where we
- // didn't *intend* to merge despite non-zero loop predecessors.
- BlockToChain[BestSucc]->LoopPredecessors = 0;
- }
-
// 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
// this point. This won't be a fallthrough, but it will increase locality.
@@ -454,19 +477,28 @@ void MachineBlockPlacement::buildChain(
BestSucc = selectBestCandidateBlock(Chain, BlockWorkList, BlockFilter);
if (!BestSucc) {
- DEBUG(dbgs() << "Finished forming chain for header block "
- << getBlockNum(*Chain.begin()) << "\n");
- return;
+ BestSucc = getFirstUnplacedBlock(Chain, Blocks, PrevUnplacedBlockIdx);
+ if (!BestSucc)
+ break;
+
+ DEBUG(dbgs() << "Unnatural loop CFG detected, forcibly merging the "
+ "layout successor until the CFG reduces\n");
}
// Place this block, updating the datastructures to reflect its placement.
BlockChain &SuccChain = *BlockToChain[BestSucc];
+ // Zero out LoopPredecessors for the successor we're about to merge in case
+ // we selected a successor that didn't fit naturally into the CFG.
+ SuccChain.LoopPredecessors = 0;
DEBUG(dbgs() << "Merging from " << getBlockNum(BB)
<< " to " << getBlockNum(BestSucc) << "\n");
markChainSuccessors(SuccChain, LoopHeaderBB, BlockWorkList, BlockFilter);
Chain.merge(BestSucc, &SuccChain);
BB = *llvm::prior(Chain.end());
- }
+ };
+
+ DEBUG(dbgs() << "Finished forming chain for header block "
+ << getBlockNum(*Chain.begin()) << "\n");
}
/// \brief Forms basic block chains from the natural loop structures.
@@ -484,6 +516,7 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F,
SmallVector<MachineBasicBlock *, 16> BlockWorkList;
BlockFilterSet LoopBlockSet(L.block_begin(), L.block_end());
+ BlockChain &LoopChain = *BlockToChain[L.getHeader()];
// FIXME: This is a really lame way of walking the chains in the loop: we
// walk the blocks, and use a set to prevent visiting a particular chain
@@ -513,8 +546,8 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F,
BlockWorkList.push_back(*BI);
}
- BlockChain &LoopChain = *BlockToChain[L.getHeader()];
- buildChain(*L.block_begin(), LoopChain, BlockWorkList, &LoopBlockSet);
+ buildChain(*L.block_begin(), LoopChain, L.getBlocks(), BlockWorkList,
+ &LoopBlockSet);
DEBUG({
// Crash at the end so we get all of the debugging output first.
@@ -561,11 +594,17 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
++LI)
buildLoopChains(F, **LI);
+ // We need a vector of blocks so that buildChain can handle unnatural CFG
+ // constructs by searching for unplaced blocks and just concatenating them.
+ SmallVector<MachineBasicBlock *, 16> Blocks;
+ Blocks.reserve(F.size());
+
SmallVector<MachineBasicBlock *, 16> BlockWorkList;
SmallPtrSet<BlockChain *, 4> UpdatedPreds;
for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
MachineBasicBlock *BB = &*FI;
+ Blocks.push_back(BB);
BlockChain &Chain = *BlockToChain[BB];
if (!UpdatedPreds.insert(&Chain))
continue;
@@ -588,7 +627,7 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
}
BlockChain &FunctionChain = *BlockToChain[&F.front()];
- buildChain(&F.front(), FunctionChain, BlockWorkList);
+ buildChain(&F.front(), FunctionChain, Blocks, BlockWorkList);
typedef SmallPtrSet<MachineBasicBlock *, 16> FunctionBlockSetType;
DEBUG({
generated by cgit v1.2.3-18-g5258 (git 2.32.0) at 2024-11-22 16:00:17 +0000