diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/LoopRotation.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/LoopRotation.cpp | 491 |
1 files changed, 208 insertions, 283 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/contrib/llvm/lib/Transforms/Scalar/LoopRotation.cpp index 65acc1d..95e1578 100644 --- a/contrib/llvm/lib/Transforms/Scalar/LoopRotation.cpp +++ b/contrib/llvm/lib/Transforms/Scalar/LoopRotation.cpp @@ -15,16 +15,16 @@ #include "llvm/Transforms/Scalar.h" #include "llvm/Function.h" #include "llvm/IntrinsicInst.h" +#include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/LoopPass.h" -#include "llvm/Analysis/Dominators.h" +#include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/SSAUpdater.h" -#include "llvm/Support/CommandLine.h" +#include "llvm/Transforms/Utils/ValueMapper.h" #include "llvm/Support/Debug.h" #include "llvm/ADT/Statistic.h" -#include "llvm/ADT/SmallVector.h" using namespace llvm; #define MAX_HEADER_SIZE 16 @@ -35,16 +35,13 @@ namespace { class LoopRotate : public LoopPass { public: static char ID; // Pass ID, replacement for typeid - LoopRotate() : LoopPass(ID) {} - - // Rotate Loop L as many times as possible. Return true if - // loop is rotated at least once. - bool runOnLoop(Loop *L, LPPassManager &LPM); + LoopRotate() : LoopPass(ID) { + initializeLoopRotatePass(*PassRegistry::getPassRegistry()); + } // LCSSA form makes instruction renaming easier. virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.addPreserved<DominatorTree>(); - AU.addPreserved<DominanceFrontier>(); AU.addRequired<LoopInfo>(); AU.addPreserved<LoopInfo>(); AU.addRequiredID(LoopSimplifyID); @@ -54,79 +51,119 @@ namespace { AU.addPreserved<ScalarEvolution>(); } - // Helper functions - - /// Do actual work - bool rotateLoop(Loop *L, LPPassManager &LPM); + bool runOnLoop(Loop *L, LPPassManager &LPM); + bool rotateLoop(Loop *L); - /// Initialize local data - void initialize(); - - /// After loop rotation, loop pre-header has multiple sucessors. - /// Insert one forwarding basic block to ensure that loop pre-header - /// has only one successor. - void preserveCanonicalLoopForm(LPPassManager &LPM); - private: - Loop *L; - BasicBlock *OrigHeader; - BasicBlock *OrigPreHeader; - BasicBlock *OrigLatch; - BasicBlock *NewHeader; - BasicBlock *Exit; - LPPassManager *LPM_Ptr; + LoopInfo *LI; }; } char LoopRotate::ID = 0; -INITIALIZE_PASS(LoopRotate, "loop-rotate", "Rotate Loops", false, false); +INITIALIZE_PASS_BEGIN(LoopRotate, "loop-rotate", "Rotate Loops", false, false) +INITIALIZE_PASS_DEPENDENCY(LoopInfo) +INITIALIZE_PASS_DEPENDENCY(LoopSimplify) +INITIALIZE_PASS_DEPENDENCY(LCSSA) +INITIALIZE_PASS_END(LoopRotate, "loop-rotate", "Rotate Loops", false, false) Pass *llvm::createLoopRotatePass() { return new LoopRotate(); } /// Rotate Loop L as many times as possible. Return true if /// the loop is rotated at least once. -bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) { - - bool RotatedOneLoop = false; - initialize(); - LPM_Ptr = &LPM; +bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) { + LI = &getAnalysis<LoopInfo>(); // One loop can be rotated multiple times. - while (rotateLoop(Lp,LPM)) { - RotatedOneLoop = true; - initialize(); - } + bool MadeChange = false; + while (rotateLoop(L)) + MadeChange = true; - return RotatedOneLoop; + return MadeChange; } -/// Rotate loop LP. Return true if the loop is rotated. -bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { - L = Lp; - - OrigPreHeader = L->getLoopPreheader(); - if (!OrigPreHeader) return false; - - OrigLatch = L->getLoopLatch(); - if (!OrigLatch) return false; +/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the +/// old header into the preheader. If there were uses of the values produced by +/// these instruction that were outside of the loop, we have to insert PHI nodes +/// to merge the two values. Do this now. +static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader, + BasicBlock *OrigPreheader, + ValueToValueMapTy &ValueMap) { + // Remove PHI node entries that are no longer live. + BasicBlock::iterator I, E = OrigHeader->end(); + for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I) + PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader)); + + // Now fix up users of the instructions in OrigHeader, inserting PHI nodes + // as necessary. + SSAUpdater SSA; + for (I = OrigHeader->begin(); I != E; ++I) { + Value *OrigHeaderVal = I; + + // If there are no uses of the value (e.g. because it returns void), there + // is nothing to rewrite. + if (OrigHeaderVal->use_empty()) + continue; + + Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal]; - OrigHeader = L->getHeader(); + // The value now exits in two versions: the initial value in the preheader + // and the loop "next" value in the original header. + SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName()); + SSA.AddAvailableValue(OrigHeader, OrigHeaderVal); + SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal); + + // Visit each use of the OrigHeader instruction. + for (Value::use_iterator UI = OrigHeaderVal->use_begin(), + UE = OrigHeaderVal->use_end(); UI != UE; ) { + // Grab the use before incrementing the iterator. + Use &U = UI.getUse(); + + // Increment the iterator before removing the use from the list. + ++UI; + + // SSAUpdater can't handle a non-PHI use in the same block as an + // earlier def. We can easily handle those cases manually. + Instruction *UserInst = cast<Instruction>(U.getUser()); + if (!isa<PHINode>(UserInst)) { + BasicBlock *UserBB = UserInst->getParent(); + + // The original users in the OrigHeader are already using the + // original definitions. + if (UserBB == OrigHeader) + continue; + + // Users in the OrigPreHeader need to use the value to which the + // original definitions are mapped. + if (UserBB == OrigPreheader) { + U = OrigPreHeaderVal; + continue; + } + } + + // Anything else can be handled by SSAUpdater. + SSA.RewriteUse(U); + } + } +} +/// Rotate loop LP. Return true if the loop is rotated. +bool LoopRotate::rotateLoop(Loop *L) { // If the loop has only one block then there is not much to rotate. if (L->getBlocks().size() == 1) return false; - + + BasicBlock *OrigHeader = L->getHeader(); + + BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator()); + if (BI == 0 || BI->isUnconditional()) + return false; + // If the loop header is not one of the loop exiting blocks then // either this loop is already rotated or it is not // suitable for loop rotation transformations. if (!L->isLoopExiting(OrigHeader)) return false; - BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator()); - if (!BI) - return false; - assert(BI->isConditional() && "Branch Instruction is not conditional"); - // Updating PHInodes in loops with multiple exits adds complexity. // Keep it simple, and restrict loop rotation to loops with one exit only. // In future, lift this restriction and support for multiple exits if @@ -136,24 +173,18 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { if (ExitBlocks.size() > 1) return false; - // Check size of original header and reject - // loop if it is very big. - unsigned Size = 0; - - // FIXME: Use common api to estimate size. - for (BasicBlock::const_iterator OI = OrigHeader->begin(), - OE = OrigHeader->end(); OI != OE; ++OI) { - if (isa<PHINode>(OI)) - continue; // PHI nodes don't count. - if (isa<DbgInfoIntrinsic>(OI)) - continue; // Debug intrinsics don't count as size. - ++Size; + // Check size of original header and reject loop if it is very big. + { + CodeMetrics Metrics; + Metrics.analyzeBasicBlock(OrigHeader); + if (Metrics.NumInsts > MAX_HEADER_SIZE) + return false; } - if (Size > MAX_HEADER_SIZE) - return false; - // Now, this loop is suitable for rotation. + BasicBlock *OrigPreheader = L->getLoopPreheader(); + BasicBlock *OrigLatch = L->getLoopLatch(); + assert(OrigPreheader && OrigLatch && "Loop not in canonical form?"); // Anything ScalarEvolution may know about this loop or the PHI nodes // in its header will soon be invalidated. @@ -163,8 +194,8 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { // Find new Loop header. NewHeader is a Header's one and only successor // that is inside loop. Header's other successor is outside the // loop. Otherwise loop is not suitable for rotation. - Exit = BI->getSuccessor(0); - NewHeader = BI->getSuccessor(1); + BasicBlock *Exit = BI->getSuccessor(0); + BasicBlock *NewHeader = BI->getSuccessor(1); if (L->contains(Exit)) std::swap(Exit, NewHeader); assert(NewHeader && "Unable to determine new loop header"); @@ -180,20 +211,54 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { // Begin by walking OrigHeader and populating ValueMap with an entry for // each Instruction. BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end(); - DenseMap<const Value *, Value *> ValueMap; + ValueToValueMapTy ValueMap; // For PHI nodes, the value available in OldPreHeader is just the // incoming value from OldPreHeader. for (; PHINode *PN = dyn_cast<PHINode>(I); ++I) - ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreHeader)); + ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreheader)); - // For the rest of the instructions, create a clone in the OldPreHeader. - TerminatorInst *LoopEntryBranch = OrigPreHeader->getTerminator(); - for (; I != E; ++I) { - Instruction *C = I->clone(); - C->setName(I->getName()); - C->insertBefore(LoopEntryBranch); - ValueMap[I] = C; + // For the rest of the instructions, either hoist to the OrigPreheader if + // possible or create a clone in the OldPreHeader if not. + TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator(); + while (I != E) { + Instruction *Inst = I++; + + // If the instruction's operands are invariant and it doesn't read or write + // memory, then it is safe to hoist. Doing this doesn't change the order of + // execution in the preheader, but does prevent the instruction from + // executing in each iteration of the loop. This means it is safe to hoist + // something that might trap, but isn't safe to hoist something that reads + // memory (without proving that the loop doesn't write). + if (L->hasLoopInvariantOperands(Inst) && + !Inst->mayReadFromMemory() && !Inst->mayWriteToMemory() && + !isa<TerminatorInst>(Inst) && !isa<DbgInfoIntrinsic>(Inst)) { + Inst->moveBefore(LoopEntryBranch); + continue; + } + + // Otherwise, create a duplicate of the instruction. + Instruction *C = Inst->clone(); + + // Eagerly remap the operands of the instruction. + RemapInstruction(C, ValueMap, + RF_NoModuleLevelChanges|RF_IgnoreMissingEntries); + + // With the operands remapped, see if the instruction constant folds or is + // otherwise simplifyable. This commonly occurs because the entry from PHI + // nodes allows icmps and other instructions to fold. + Value *V = SimplifyInstruction(C); + if (V && LI->replacementPreservesLCSSAForm(C, V)) { + // If so, then delete the temporary instruction and stick the folded value + // in the map. + delete C; + ValueMap[Inst] = V; + } else { + // Otherwise, stick the new instruction into the new block! + C->setName(Inst->getName()); + C->insertBefore(LoopEntryBranch); + ValueMap[Inst] = C; + } } // Along with all the other instructions, we just cloned OrigHeader's @@ -203,221 +268,81 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) for (BasicBlock::iterator BI = TI->getSuccessor(i)->begin(); PHINode *PN = dyn_cast<PHINode>(BI); ++BI) - PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreHeader); + PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader); // Now that OrigPreHeader has a clone of OrigHeader's terminator, remove // OrigPreHeader's old terminator (the original branch into the loop), and // remove the corresponding incoming values from the PHI nodes in OrigHeader. LoopEntryBranch->eraseFromParent(); - for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I) - PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreHeader)); - // Now fix up users of the instructions in OrigHeader, inserting PHI nodes - // as necessary. - SSAUpdater SSA; - for (I = OrigHeader->begin(); I != E; ++I) { - Value *OrigHeaderVal = I; - Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal]; - - // The value now exits in two versions: the initial value in the preheader - // and the loop "next" value in the original header. - SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName()); - SSA.AddAvailableValue(OrigHeader, OrigHeaderVal); - SSA.AddAvailableValue(OrigPreHeader, OrigPreHeaderVal); - - // Visit each use of the OrigHeader instruction. - for (Value::use_iterator UI = OrigHeaderVal->use_begin(), - UE = OrigHeaderVal->use_end(); UI != UE; ) { - // Grab the use before incrementing the iterator. - Use &U = UI.getUse(); - - // Increment the iterator before removing the use from the list. - ++UI; - - // SSAUpdater can't handle a non-PHI use in the same block as an - // earlier def. We can easily handle those cases manually. - Instruction *UserInst = cast<Instruction>(U.getUser()); - if (!isa<PHINode>(UserInst)) { - BasicBlock *UserBB = UserInst->getParent(); - - // The original users in the OrigHeader are already using the - // original definitions. - if (UserBB == OrigHeader) - continue; - - // Users in the OrigPreHeader need to use the value to which the - // original definitions are mapped. - if (UserBB == OrigPreHeader) { - U = OrigPreHeaderVal; - continue; - } - } - - // Anything else can be handled by SSAUpdater. - SSA.RewriteUse(U); - } - } + // If there were any uses of instructions in the duplicated block outside the + // loop, update them, inserting PHI nodes as required + RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap); // NewHeader is now the header of the loop. L->moveToHeader(NewHeader); + assert(L->getHeader() == NewHeader && "Latch block is our new header"); - // Move the original header to the bottom of the loop, where it now more - // naturally belongs. This isn't necessary for correctness, and CodeGen can - // usually reorder blocks on its own to fix things like this up, but it's - // still nice to keep the IR readable. - // - // The original header should have only one predecessor at this point, since - // we checked that the loop had a proper preheader and unique backedge before - // we started. - assert(OrigHeader->getSinglePredecessor() && - "Original loop header has too many predecessors after loop rotation!"); - OrigHeader->moveAfter(OrigHeader->getSinglePredecessor()); - - // Also, since this original header only has one predecessor, zap its - // PHI nodes, which are now trivial. - FoldSingleEntryPHINodes(OrigHeader); - - // TODO: We could just go ahead and merge OrigHeader into its predecessor - // at this point, if we don't mind updating dominator info. - - // Establish a new preheader, update dominators, etc. - preserveCanonicalLoopForm(LPM); - - ++NumRotated; - return true; -} - -/// Initialize local data -void LoopRotate::initialize() { - L = NULL; - OrigHeader = NULL; - OrigPreHeader = NULL; - NewHeader = NULL; - Exit = NULL; -} - -/// After loop rotation, loop pre-header has multiple sucessors. -/// Insert one forwarding basic block to ensure that loop pre-header -/// has only one successor. -void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) { - - // Right now original pre-header has two successors, new header and - // exit block. Insert new block between original pre-header and - // new header such that loop's new pre-header has only one successor. - BasicBlock *NewPreHeader = BasicBlock::Create(OrigHeader->getContext(), - "bb.nph", - OrigHeader->getParent(), - NewHeader); - LoopInfo &LI = getAnalysis<LoopInfo>(); - if (Loop *PL = LI.getLoopFor(OrigPreHeader)) - PL->addBasicBlockToLoop(NewPreHeader, LI.getBase()); - BranchInst::Create(NewHeader, NewPreHeader); - BranchInst *OrigPH_BI = cast<BranchInst>(OrigPreHeader->getTerminator()); - if (OrigPH_BI->getSuccessor(0) == NewHeader) - OrigPH_BI->setSuccessor(0, NewPreHeader); - else { - assert(OrigPH_BI->getSuccessor(1) == NewHeader && - "Unexpected original pre-header terminator"); - OrigPH_BI->setSuccessor(1, NewPreHeader); - } - - PHINode *PN; - for (BasicBlock::iterator I = NewHeader->begin(); - (PN = dyn_cast<PHINode>(I)); ++I) { - int index = PN->getBasicBlockIndex(OrigPreHeader); - assert(index != -1 && "Expected incoming value from Original PreHeader"); - PN->setIncomingBlock(index, NewPreHeader); - assert(PN->getBasicBlockIndex(OrigPreHeader) == -1 && - "Expected only one incoming value from Original PreHeader"); - } - - if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) { - DT->addNewBlock(NewPreHeader, OrigPreHeader); - DT->changeImmediateDominator(L->getHeader(), NewPreHeader); - DT->changeImmediateDominator(Exit, OrigPreHeader); - for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end(); - BI != BE; ++BI) { - BasicBlock *B = *BI; - if (L->getHeader() != B) { - DomTreeNode *Node = DT->getNode(B); - if (Node && Node->getBlock() == OrigHeader) - DT->changeImmediateDominator(*BI, L->getHeader()); - } - } - DT->changeImmediateDominator(OrigHeader, OrigLatch); - } - - if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>()) { - // New Preheader's dominance frontier is Exit block. - DominanceFrontier::DomSetType NewPHSet; - NewPHSet.insert(Exit); - DF->addBasicBlock(NewPreHeader, NewPHSet); - - // New Header's dominance frontier now includes itself and Exit block - DominanceFrontier::iterator HeadI = DF->find(L->getHeader()); - if (HeadI != DF->end()) { - DominanceFrontier::DomSetType & HeaderSet = HeadI->second; - HeaderSet.clear(); - HeaderSet.insert(L->getHeader()); - HeaderSet.insert(Exit); - } else { - DominanceFrontier::DomSetType HeaderSet; - HeaderSet.insert(L->getHeader()); - HeaderSet.insert(Exit); - DF->addBasicBlock(L->getHeader(), HeaderSet); - } - - // Original header (new Loop Latch)'s dominance frontier is Exit. - DominanceFrontier::iterator LatchI = DF->find(L->getLoopLatch()); - if (LatchI != DF->end()) { - DominanceFrontier::DomSetType &LatchSet = LatchI->second; - LatchSet = LatchI->second; - LatchSet.clear(); - LatchSet.insert(Exit); - } else { - DominanceFrontier::DomSetType LatchSet; - LatchSet.insert(Exit); - DF->addBasicBlock(L->getHeader(), LatchSet); + // At this point, we've finished our major CFG changes. As part of cloning + // the loop into the preheader we've simplified instructions and the + // duplicated conditional branch may now be branching on a constant. If it is + // branching on a constant and if that constant means that we enter the loop, + // then we fold away the cond branch to an uncond branch. This simplifies the + // loop in cases important for nested loops, and it also means we don't have + // to split as many edges. + BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator()); + assert(PHBI->isConditional() && "Should be clone of BI condbr!"); + if (!isa<ConstantInt>(PHBI->getCondition()) || + PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero()) + != NewHeader) { + // The conditional branch can't be folded, handle the general case. + // Update DominatorTree to reflect the CFG change we just made. Then split + // edges as necessary to preserve LoopSimplify form. + if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) { + // Since OrigPreheader now has the conditional branch to Exit block, it is + // the dominator of Exit. + DT->changeImmediateDominator(Exit, OrigPreheader); + DT->changeImmediateDominator(NewHeader, OrigPreheader); + + // Update OrigHeader to be dominated by the new header block. + DT->changeImmediateDominator(OrigHeader, OrigLatch); } - - // If a loop block dominates new loop latch then add to its frontiers - // new header and Exit and remove new latch (which is equal to original - // header). - BasicBlock *NewLatch = L->getLoopLatch(); - - assert(NewLatch == OrigHeader && "NewLatch is inequal to OrigHeader"); - + + // Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and + // thus is not a preheader anymore. Split the edge to form a real preheader. + BasicBlock *NewPH = SplitCriticalEdge(OrigPreheader, NewHeader, this); + NewPH->setName(NewHeader->getName() + ".lr.ph"); + + // Preserve canonical loop form, which means that 'Exit' should have only one + // predecessor. + BasicBlock *ExitSplit = SplitCriticalEdge(L->getLoopLatch(), Exit, this); + ExitSplit->moveBefore(Exit); + } else { + // We can fold the conditional branch in the preheader, this makes things + // simpler. The first step is to remove the extra edge to the Exit block. + Exit->removePredecessor(OrigPreheader, true /*preserve LCSSA*/); + BranchInst::Create(NewHeader, PHBI); + PHBI->eraseFromParent(); + + // With our CFG finalized, update DomTree if it is available. if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) { - for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end(); - BI != BE; ++BI) { - BasicBlock *B = *BI; - if (DT->dominates(B, NewLatch)) { - DominanceFrontier::iterator BDFI = DF->find(B); - if (BDFI != DF->end()) { - DominanceFrontier::DomSetType &BSet = BDFI->second; - BSet.erase(NewLatch); - BSet.insert(L->getHeader()); - BSet.insert(Exit); - } else { - DominanceFrontier::DomSetType BSet; - BSet.insert(L->getHeader()); - BSet.insert(Exit); - DF->addBasicBlock(B, BSet); - } - } - } + // Update OrigHeader to be dominated by the new header block. + DT->changeImmediateDominator(NewHeader, OrigPreheader); + DT->changeImmediateDominator(OrigHeader, OrigLatch); } } - - // Preserve canonical loop form, which means Exit block should - // have only one predecessor. - SplitEdge(L->getLoopLatch(), Exit, this); - - assert(NewHeader && L->getHeader() == NewHeader && - "Invalid loop header after loop rotation"); - assert(NewPreHeader && L->getLoopPreheader() == NewPreHeader && - "Invalid loop preheader after loop rotation"); - assert(L->getLoopLatch() && - "Invalid loop latch after loop rotation"); + + assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation"); + assert(L->getLoopLatch() && "Invalid loop latch after loop rotation"); + + // Now that the CFG and DomTree are in a consistent state again, try to merge + // the OrigHeader block into OrigLatch. This will succeed if they are + // connected by an unconditional branch. This is just a cleanup so the + // emitted code isn't too gross in this common case. + MergeBlockIntoPredecessor(OrigHeader, this); + + ++NumRotated; + return true; } + |
