diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h index 47d68956e4f..e766d729e1b 100644 --- a/include/llvm/Transforms/Utils/BasicBlockUtils.h +++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h @@ -43,11 +43,9 @@ void FoldSingleEntryPHINodes(BasicBlock *BB); /// it is ultimately unused or if it reaches an unused cycle. void DeleteDeadPHIs(BasicBlock *BB); -/// MergeBlockIntoPredecessor - Folds a basic block into its predecessor if it -/// only has one predecessor, and that predecessor only has one successor. -/// If a Pass is given, the LoopInfo and DominatorTree analyses will be kept -/// current. Returns the combined block, or null if no merging was performed. -BasicBlock *MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P = 0); +/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, +/// if possible. The return value indicates success or failure. +bool MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P = 0); // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) // with a value, then remove and delete the original instruction. diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp index e7f33d30b66..f3c175469ac 100644 --- a/lib/Transforms/Utils/BasicBlockUtils.cpp +++ b/lib/Transforms/Utils/BasicBlockUtils.cpp @@ -92,28 +92,54 @@ void llvm::DeleteDeadPHIs(BasicBlock *BB) { RecursivelyDeleteDeadPHINode(PN); } -/// MergeBlockIntoPredecessor - Folds a basic block into its predecessor if it -/// only has one predecessor, and that predecessor only has one successor. -/// If a Pass is given, the LoopInfo and DominatorTree analyses will be kept -/// current. Returns the combined block, or null if no merging was performed. -BasicBlock *llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) { - // Don't merge if the block has multiple predecessors. - BasicBlock *PredBB = BB->getSinglePredecessor(); - if (!PredBB) return 0; - // Don't merge if the predecessor has multiple successors. - if (PredBB->getTerminator()->getNumSuccessors() != 1) return 0; - // Don't break self-loops. - if (PredBB == BB) return 0; - // Don't break invokes. - if (isa(PredBB->getTerminator())) return 0; +/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, +/// if possible. The return value indicates success or failure. +bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) { + pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); + // Can't merge the entry block. + if (pred_begin(BB) == pred_end(BB)) return false; - // Resolve any PHI nodes at the start of the block. They are all - // guaranteed to have exactly one entry if they exist, unless there are - // multiple duplicate (but guaranteed to be equal) entries for the - // incoming edges. This occurs when there are multiple edges from - // PredBB to BB. - FoldSingleEntryPHINodes(BB); + BasicBlock *PredBB = *PI++; + for (; PI != PE; ++PI) // Search all predecessors, see if they are all same + if (*PI != PredBB) { + PredBB = 0; // There are multiple different predecessors... + break; + } + + // Can't merge if there are multiple predecessors. + if (!PredBB) return false; + // Don't break self-loops. + if (PredBB == BB) return false; + // Don't break invokes. + if (isa(PredBB->getTerminator())) return false; + + succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB)); + BasicBlock* OnlySucc = BB; + for (; SI != SE; ++SI) + if (*SI != OnlySucc) { + OnlySucc = 0; // There are multiple distinct successors! + break; + } + + // Can't merge if there are multiple successors. + if (!OnlySucc) return false; + // Can't merge if there is PHI loop. + for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) { + if (PHINode *PN = dyn_cast(BI)) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + if (PN->getIncomingValue(i) == PN) + return false; + } else + break; + } + + // Begin by getting rid of unneeded PHIs. + while (PHINode *PN = dyn_cast(&BB->front())) { + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + BB->getInstList().pop_front(); // Delete the phi node... + } + // Delete the unconditional branch from the predecessor... PredBB->getInstList().pop_back(); @@ -124,7 +150,7 @@ BasicBlock *llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) { // source... BB->replaceAllUsesWith(PredBB); - // If the predecessor doesn't have a name, take the successor's name. + // Inherit predecessors name if it exists. if (!PredBB->hasName()) PredBB->takeName(BB); @@ -143,14 +169,12 @@ BasicBlock *llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) { DT->eraseNode(BB); } } - // Notify LoopInfo that the block is removed. - if (LoopInfo *LI = P->getAnalysisIfAvailable()) - LI->removeBlock(BB); } BB->eraseFromParent(); - return PredBB; + + return true; } /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp index 9b68df05b84..d68427afce7 100644 --- a/lib/Transforms/Utils/LoopUnroll.cpp +++ b/lib/Transforms/Utils/LoopUnroll.cpp @@ -49,6 +49,52 @@ static inline void RemapInstruction(Instruction *I, } } +/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it +/// only has one predecessor, and that predecessor only has one successor. +/// The LoopInfo Analysis that is passed will be kept consistent. +/// Returns the new combined block. +static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) { + // Merge basic blocks into their predecessor if there is only one distinct + // pred, and if there is only one distinct successor of the predecessor, and + // if there are no PHI nodes. + BasicBlock *OnlyPred = BB->getSinglePredecessor(); + if (!OnlyPred) return 0; + + if (OnlyPred->getTerminator()->getNumSuccessors() != 1) + return 0; + + DEBUG(errs() << "Merging: " << *BB << "into: " << *OnlyPred); + + // Resolve any PHI nodes at the start of the block. They are all + // guaranteed to have exactly one entry if they exist, unless there are + // multiple duplicate (but guaranteed to be equal) entries for the + // incoming edges. This occurs when there are multiple edges from + // OnlyPred to OnlySucc. + FoldSingleEntryPHINodes(BB); + + // Delete the unconditional branch from the predecessor... + OnlyPred->getInstList().pop_back(); + + // Move all definitions in the successor to the predecessor... + OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); + + // Make all PHI nodes that referred to BB now refer to Pred as their + // source... + BB->replaceAllUsesWith(OnlyPred); + + std::string OldName = BB->getName(); + + // Erase basic block from the function... + LI->removeBlock(BB); + BB->eraseFromParent(); + + // Inherit predecessor's name if it exists... + if (!OldName.empty() && !OnlyPred->hasName()) + OnlyPred->setName(OldName); + + return OnlyPred; +} + /// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true /// if unrolling was succesful, or false if the loop was unmodified. Unrolling /// can only fail when the loop's latch block is not terminated by a conditional @@ -287,7 +333,7 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, LoopInfo* LI, LPPassManager* LPM) } else { Term->setUnconditionalDest(Dest); // Merge adjacent basic blocks, if possible. - if (BasicBlock *Fold = MergeBlockIntoPredecessor(Dest, LI)) { + if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI)) { std::replace(Latches.begin(), Latches.end(), Dest, Fold); std::replace(Headers.begin(), Headers.end(), Dest, Fold); } diff --git a/test/Transforms/SimplifyCFG/PhiBlockMerge.ll b/test/Transforms/SimplifyCFG/PhiBlockMerge.ll index 1219dfe0749..a648efd1740 100644 --- a/test/Transforms/SimplifyCFG/PhiBlockMerge.ll +++ b/test/Transforms/SimplifyCFG/PhiBlockMerge.ll @@ -9,7 +9,6 @@ define i32 @test(i1 %a, i1 %b) { O: ; preds = %0 br i1 %b, label %N, label %Q Q: ; preds = %O - call void @foo() br label %N N: ; preds = %Q, %O ; This block should be foldable into M @@ -21,4 +20,3 @@ M: ; preds = %N, %0 ret i32 %R } -declare void @foo()