X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FUtils%2FBreakCriticalEdges.cpp;h=0c4974db10ac4c325d94ceb981ace69ec4e5d53a;hb=cb2610ea037a17115ef3a01a6bdaab4e3cfdca27;hp=2222a04e1dc7698698e2bc378af609dfa1de58de;hpb=d76efa018660e806cd87c0a24512e3c532fc1d36;p=oota-llvm.git diff --git a/lib/Transforms/Utils/BreakCriticalEdges.cpp b/lib/Transforms/Utils/BreakCriticalEdges.cpp index 2222a04e1dc..0c4974db10a 100644 --- a/lib/Transforms/Utils/BreakCriticalEdges.cpp +++ b/lib/Transforms/Utils/BreakCriticalEdges.cpp @@ -9,29 +9,119 @@ //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" -#include "llvm/Transforms/Utils/Local.h" #include "llvm/Analysis/Dominators.h" #include "llvm/Function.h" -#include "llvm/InstrTypes.h" -#include "Support/StatisticReporter.h" +#include "llvm/iTerminators.h" +#include "llvm/iPHINode.h" +#include "llvm/Support/CFG.h" +#include "Support/Statistic.h" -static Statistic<> NumBroken("break-crit-edges\t- Number of blocks inserted"); +namespace { + Statistic<> NumBroken("break-crit-edges", "Number of blocks inserted"); -class BreakCriticalEdges : public FunctionPass { -public: - virtual bool runOnFunction(Function &F); + struct BreakCriticalEdges : public FunctionPass { + virtual bool runOnFunction(Function &F); + + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); + AU.addPreservedID(LoopPreheadersID); // No preheaders deleted. + } + }; - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - AU.addPreserved(); - AU.addPreserved(); - AU.addPreserved(); + RegisterOpt X("break-crit-edges", + "Break critical edges in CFG"); +} + +// Publically exposed interface to pass... +const PassInfo *BreakCriticalEdgesID = X.getPassInfo(); +Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); } + + +// isCriticalEdge - Return true if the specified edge is a critical edge. +// Critical edges are edges from a block with multiple successors to a block +// with multiple predecessors. +// +bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum) { + assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!"); + if (TI->getNumSuccessors() == 1) return false; + + const BasicBlock *Dest = TI->getSuccessor(SuccNum); + pred_const_iterator I = pred_begin(Dest), E = pred_end(Dest); + + // If there is more than one predecessor, this is a critical edge... + assert(I != E && "No preds, but we have an edge to the block?"); + ++I; // Skip one edge due to the incoming arc from TI. + return I != E; +} + +// SplitCriticalEdge - Insert a new node node to split the critical edge. This +// will update DominatorSet, ImmediateDominator and DominatorTree information if +// it is available, thus calling this pass will not invalidate either of them. +// +void SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) { + assert(isCriticalEdge(TI, SuccNum) && + "Cannot break a critical edge, if it isn't a critical edge"); + BasicBlock *TIBB = TI->getParent(); + + // Create a new basic block, linking it into the CFG. + BasicBlock *NewBB = new BasicBlock(TIBB->getName()+"_crit_edge"); + BasicBlock *DestBB = TI->getSuccessor(SuccNum); + // Create our unconditional branch... + BranchInst *BI = new BranchInst(DestBB); + NewBB->getInstList().push_back(BI); + + // Branch to the new block, breaking the edge... + TI->setSuccessor(SuccNum, NewBB); + + // Insert the block into the function... right after the block TI lives in. + Function &F = *TIBB->getParent(); + F.getBasicBlockList().insert(TIBB->getNext(), NewBB); + + // If there are any PHI nodes in DestBB, we need to update them so that they + // merge incoming values from NewBB instead of from TIBB. + // + for (BasicBlock::iterator I = DestBB->begin(); + PHINode *PN = dyn_cast(&*I); ++I) { + // We no longer enter through TIBB, now we come in through NewBB. + PN->replaceUsesOfWith(TIBB, NewBB); } -}; -static RegisterOpt X("break-crit-edges", - "Break critical edges in CFG"); + // If we don't have a pass object, we can't update anything... + if (P == 0) return; -Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); } + // Now update analysis information. These are the analyses that we are + // currently capable of updating... + // + + // Should we update DominatorSet information? + if (DominatorSet *DS = P->getAnalysisToUpdate()) { + // The blocks that dominate the new one are the blocks that dominate TIBB + // plus the new block itself. + DominatorSet::DomSetType DomSet = DS->getDominators(TIBB); + DomSet.insert(NewBB); // A block always dominates itself. + DS->addBasicBlock(NewBB, DomSet); + } + + // Should we update ImmdediateDominator information? + if (ImmediateDominators *ID = P->getAnalysisToUpdate()) { + // TIBB is the new immediate dominator for NewBB. NewBB doesn't dominate + // anything. + ID->addNewBlock(NewBB, TIBB); + } + + // Should we update DominatorTree information? + if (DominatorTree *DT = P->getAnalysisToUpdate()) { + DominatorTree::Node *TINode = DT->getNode(TIBB); + + // The new block is not the immediate dominator for any other nodes, but + // TINode is the immediate dominator for the new node. + // + if (TINode) // Don't break unreachable code! + DT->createNewNode(NewBB, TINode); + } +} // runOnFunction - Loop over all of the edges in the CFG, breaking critical // edges as they are found. @@ -40,12 +130,13 @@ bool BreakCriticalEdges::runOnFunction(Function &F) { bool Changed = false; for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { TerminatorInst *TI = I->getTerminator(); - for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) - if (isCriticalEdge(TI, i)) { - SplitCriticalEdge(TI, i, this); - ++NumBroken; - Changed = true; - } + if (TI->getNumSuccessors() > 1) + for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) + if (isCriticalEdge(TI, i)) { + SplitCriticalEdge(TI, i, this); + ++NumBroken; + Changed = true; + } } return Changed;