diff options
| -rw-r--r-- | include/llvm/Transforms/Utils/BasicBlockUtils.h | 17 | ||||
| -rw-r--r-- | lib/Transforms/Utils/BasicBlockUtils.cpp | 96 |
2 files changed, 112 insertions, 1 deletions
diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h index 90eabef12f..d0a3773d11 100644 --- a/include/llvm/Transforms/Utils/BasicBlockUtils.h +++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h @@ -174,6 +174,23 @@ BasicBlock *SplitBlockPredecessors(BasicBlock *BB, BasicBlock *const *Preds, unsigned NumPreds, const char *Suffix, Pass *P = 0); +/// SplitLandingPadPredecessors - This method transforms the landing pad, +/// OrigBB, by introducing two new basic blocks into the function. One of those +/// new basic blocks gets the predecessors listed in Preds. The other basic +/// block gets the remaining predecessors of OrigBB. The landingpad instruction +/// OrigBB is clone into both of the new basic blocks. The new blocks are given +/// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. +/// +/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, +/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular, +/// it does not preserve LoopSimplify (because it's complicated to handle the +/// case where one of the edges being split is an exit of a loop with other +/// exits). +/// +void SplitLandingPadPredecessors(BasicBlock *OrigBB,ArrayRef<BasicBlock*> Preds, + const char *Suffix, const char *Suffix2, + Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs); + /// FoldReturnIntoUncondBranch - This method duplicates the specified return /// instruction into a predecessor which ends in an unconditional branch. If /// the return instruction returns a value defined by a PHI, propagate the diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp index 6da3ca5287..5d7f330bfd 100644 --- a/lib/Transforms/Utils/BasicBlockUtils.cpp +++ b/lib/Transforms/Utils/BasicBlockUtils.cpp @@ -323,16 +323,17 @@ static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB, LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>(); Loop *L = LI ? LI->getLoopFor(OldBB) : 0; - bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); // If we need to preserve loop analyses, collect some information about how // this split will affect loops. bool IsLoopEntry = !!L; bool SplitMakesNewLoopHeader = false; if (LI) { + bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); for (ArrayRef<BasicBlock*>::iterator i = Preds.begin(), e = Preds.end(); i != e; ++i) { BasicBlock *Pred = *i; + // If we need to preserve LCSSA, determine if any of the preds is a loop // exit. if (PreserveLCSSA) @@ -493,6 +494,99 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, return NewBB; } +/// SplitLandingPadPredecessors - This method transforms the landing pad, +/// OrigBB, by introducing two new basic blocks into the function. One of those +/// new basic blocks gets the predecessors listed in Preds. The other basic +/// block gets the remaining predecessors of OrigBB. The landingpad instruction +/// OrigBB is clone into both of the new basic blocks. The new blocks are given +/// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. +/// +/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, +/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular, +/// it does not preserve LoopSimplify (because it's complicated to handle the +/// case where one of the edges being split is an exit of a loop with other +/// exits). +/// +void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB, + ArrayRef<BasicBlock*> Preds, + const char *Suffix1, const char *Suffix2, + Pass *P, + SmallVectorImpl<BasicBlock*> &NewBBs) { + assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!"); + + // Create a new basic block for OrigBB's predecessors listed in Preds. Insert + // it right before the original block. + BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(), + OrigBB->getName() + Suffix1, + OrigBB->getParent(), OrigBB); + NewBBs.push_back(NewBB1); + + // The new block unconditionally branches to the old block. + BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1); + + // Move the edges from Preds to point to NewBB1 instead of OrigBB. + for (unsigned i = 0, e = Preds.size(); i != e; ++i) { + // This is slightly more strict than necessary; the minimum requirement + // is that there be no more than one indirectbr branching to BB. And + // all BlockAddress uses would need to be updated. + assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) && + "Cannot split an edge from an IndirectBrInst"); + Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1); + } + + // Update DominatorTree, LoopInfo, and LCCSA analysis information. + bool HasLoopExit = false; + UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit); + + // Update the PHI nodes in OrigBB with the values coming from NewBB1. + UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit); + + // Create another basic block for the rest of OrigBB's predecessors. + BasicBlock *NewBB2 = BasicBlock::Create(OrigBB->getContext(), + OrigBB->getName() + Suffix2, + OrigBB->getParent(), OrigBB); + NewBBs.push_back(NewBB2); + + // The new block unconditionally branches to the old block. + BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2); + + // Move the remaining edges from OrigBB to point to NewBB2. + SmallVector<BasicBlock*, 8> NewBB2Preds; + for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB); + i != e; ) { + BasicBlock *Pred = *i++; + if (Pred == NewBB1 || Pred == NewBB2 ) continue; + assert(!isa<IndirectBrInst>(Pred->getTerminator()) && + "Cannot split an edge from an IndirectBrInst"); + Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2); + NewBB2Preds.push_back(Pred); + e = pred_end(OrigBB); + } + + // Update DominatorTree, LoopInfo, and LCCSA analysis information. + HasLoopExit = false; + UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit); + + // Update the PHI nodes in OrigBB with the values coming from NewBB2. + UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit); + + LandingPadInst *LPad = OrigBB->getLandingPadInst(); + Instruction *Clone1 = LPad->clone(); + Clone1->setName(Twine("lpad") + Suffix1); + NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1); + + Instruction *Clone2 = LPad->clone(); + Clone2->setName(Twine("lpad") + Suffix2); + NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2); + + // Create a PHI node for the two cloned landingpad instructions. + PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad); + PN->addIncoming(Clone1, NewBB1); + PN->addIncoming(Clone2, NewBB2); + LPad->replaceAllUsesWith(PN); + LPad->eraseFromParent(); +} + /// FindFunctionBackedges - Analyze the specified function to find all of the /// loop backedges in the function and return them. This is a relatively cheap /// (compared to computing dominators and loop info) analysis. |