X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FPHIElimination.cpp;h=f0057ce8ef8f3677008743012bb7bfa4963d65f3;hb=35a389344d21178ee280c2410401b2060b5b879c;hp=c4f2cc7a75d382c0ae089b21da07245ab5913ba1;hpb=9e97f3c2e281b1d5f89da076f37d258e3dec5597;p=oota-llvm.git diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp index c4f2cc7a75d..f0057ce8ef8 100644 --- a/lib/CodeGen/PHIElimination.cpp +++ b/lib/CodeGen/PHIElimination.cpp @@ -21,6 +21,7 @@ #include "llvm/CodeGen/MachineInstr.h" #include "llvm/CodeGen/MachineInstrBuilder.h" #include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/Target/TargetInstrInfo.h" #include "llvm/Function.h" #include "llvm/Target/TargetMachine.h" #include "llvm/ADT/SmallPtrSet.h" @@ -35,11 +36,7 @@ using namespace llvm; STATISTIC(NumAtomic, "Number of atomic phis lowered"); STATISTIC(NumSplits, "Number of critical edges split on demand"); - -static cl::opt -SplitEdges("split-phi-edges", - cl::desc("Split critical edges during phi elimination"), - cl::init(false), cl::Hidden); +STATISTIC(NumReused, "Number of reused lowered phis"); char PHIElimination::ID = 0; static RegisterPass @@ -50,26 +47,20 @@ const PassInfo *const llvm::PHIEliminationID = &X; void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const { AU.addPreserved(); AU.addPreserved(); - if (SplitEdges) { - AU.addRequired(); - } else { - AU.setPreservesCFG(); - AU.addPreservedID(MachineLoopInfoID); - } + // rdar://7401784 This would be nice: + // AU.addPreservedID(MachineLoopInfoID); MachineFunctionPass::getAnalysisUsage(AU); } bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &Fn) { MRI = &Fn.getRegInfo(); - PHIDefs.clear(); - PHIKills.clear(); bool Changed = false; // Split critical edges to help the coalescer - if (SplitEdges) + if (LiveVariables *LV = getAnalysisIfAvailable()) for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) - Changed |= SplitPHIEdges(Fn, *I); + Changed |= SplitPHIEdges(Fn, *I, *LV); // Populate VRegPHIUseCount analyzePHINodes(Fn); @@ -79,14 +70,20 @@ bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &Fn) { Changed |= EliminatePHINodes(Fn, *I); // Remove dead IMPLICIT_DEF instructions. - for (SmallPtrSet::iterator I = ImpDefs.begin(), + for (SmallPtrSet::iterator I = ImpDefs.begin(), E = ImpDefs.end(); I != E; ++I) { MachineInstr *DefMI = *I; unsigned DefReg = DefMI->getOperand(0).getReg(); - if (MRI->use_empty(DefReg)) + if (MRI->use_nodbg_empty(DefReg)) DefMI->eraseFromParent(); } + // Clean up the lowered PHI instructions. + for (LoweredPHIMap::iterator I = LoweredPHIs.begin(), E = LoweredPHIs.end(); + I != E; ++I) + Fn.DeleteMachineInstr(I->first); + + LoweredPHIs.clear(); ImpDefs.clear(); VRegPHIUseCount.clear(); return Changed; @@ -97,14 +94,14 @@ bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &Fn) { /// bool llvm::PHIElimination::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { - if (MBB.empty() || MBB.front().getOpcode() != TargetInstrInfo::PHI) + if (MBB.empty() || !MBB.front().isPHI()) return false; // Quick exit for basic blocks without PHIs. // Get an iterator to the first instruction after the last PHI node (this may // also be the end of the basic block). MachineBasicBlock::iterator AfterPHIsIt = SkipPHIsAndLabels(MBB, MBB.begin()); - while (MBB.front().getOpcode() == TargetInstrInfo::PHI) + while (MBB.front().isPHI()) LowerAtomicPHINode(MBB, AfterPHIsIt); return true; @@ -117,7 +114,7 @@ static bool isSourceDefinedByImplicitDef(const MachineInstr *MPhi, for (unsigned i = 1; i != MPhi->getNumOperands(); i += 2) { unsigned SrcReg = MPhi->getOperand(i).getReg(); const MachineInstr *DefMI = MRI->getVRegDef(SrcReg); - if (!DefMI || DefMI->getOpcode() != TargetInstrInfo::IMPLICIT_DEF) + if (!DefMI || !DefMI->isImplicitDef()) return false; } return true; @@ -177,6 +174,7 @@ llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB, void llvm::PHIElimination::LowerAtomicPHINode( MachineBasicBlock &MBB, MachineBasicBlock::iterator AfterPHIsIt) { + ++NumAtomic; // Unlink the PHI node from the basic block, but don't delete the PHI yet. MachineInstr *MPhi = MBB.remove(MBB.begin()); @@ -188,6 +186,7 @@ void llvm::PHIElimination::LowerAtomicPHINode( MachineFunction &MF = *MBB.getParent(); const TargetRegisterClass *RC = MF.getRegInfo().getRegClass(DestReg); unsigned IncomingReg = 0; + bool reusedIncoming = false; // Is IncomingReg reused from an earlier PHI? // Insert a register to register copy at the top of the current block (but // after any remaining phi nodes) which copies the new incoming register @@ -197,24 +196,44 @@ void llvm::PHIElimination::LowerAtomicPHINode( // If all sources of a PHI node are implicit_def, just emit an // implicit_def instead of a copy. BuildMI(MBB, AfterPHIsIt, MPhi->getDebugLoc(), - TII->get(TargetInstrInfo::IMPLICIT_DEF), DestReg); + TII->get(TargetOpcode::IMPLICIT_DEF), DestReg); else { - IncomingReg = MF.getRegInfo().createVirtualRegister(RC); + // Can we reuse an earlier PHI node? This only happens for critical edges, + // typically those created by tail duplication. + unsigned &entry = LoweredPHIs[MPhi]; + if (entry) { + // An identical PHI node was already lowered. Reuse the incoming register. + IncomingReg = entry; + reusedIncoming = true; + ++NumReused; + DEBUG(dbgs() << "Reusing %reg" << IncomingReg << " for " << *MPhi); + } else { + entry = IncomingReg = MF.getRegInfo().createVirtualRegister(RC); + } TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC); } - // Record PHI def. - assert(!hasPHIDef(DestReg) && "Vreg has multiple phi-defs?"); - PHIDefs[DestReg] = &MBB; - // Update live variable information if there is any. LiveVariables *LV = getAnalysisIfAvailable(); if (LV) { MachineInstr *PHICopy = prior(AfterPHIsIt); if (IncomingReg) { + LiveVariables::VarInfo &VI = LV->getVarInfo(IncomingReg); + // Increment use count of the newly created virtual register. - LV->getVarInfo(IncomingReg).NumUses++; + VI.NumUses++; + LV->setPHIJoin(IncomingReg); + + // When we are reusing the incoming register, it may already have been + // killed in this block. The old kill will also have been inserted at + // AfterPHIsIt, so it appears before the current PHICopy. + if (reusedIncoming) + if (MachineInstr *OldKill = VI.findKill(&MBB)) { + DEBUG(dbgs() << "Remove old kill from " << *OldKill); + LV->removeVirtualRegisterKilled(IncomingReg, OldKill); + DEBUG(MBB.dump()); + } // Add information to LiveVariables to know that the incoming value is // killed. Note that because the value is defined in several places (once @@ -237,7 +256,7 @@ void llvm::PHIElimination::LowerAtomicPHINode( // Adjust the VRegPHIUseCount map to account for the removal of this PHI node. for (unsigned i = 1; i != MPhi->getNumOperands(); i += 2) - --VRegPHIUseCount[BBVRegPair(MPhi->getOperand(i + 1).getMBB(), + --VRegPHIUseCount[BBVRegPair(MPhi->getOperand(i+1).getMBB()->getNumber(), MPhi->getOperand(i).getReg())]; // Now loop over all of the incoming arguments, changing them to copy into the @@ -252,13 +271,10 @@ void llvm::PHIElimination::LowerAtomicPHINode( // path the PHI. MachineBasicBlock &opBlock = *MPhi->getOperand(i*2+2).getMBB(); - // Record the kill. - PHIKills[SrcReg].insert(&opBlock); - // If source is defined by an implicit def, there is no need to insert a // copy. MachineInstr *DefMI = MRI->getVRegDef(SrcReg); - if (DefMI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF) { + if (DefMI->isImplicitDef()) { ImpDefs.insert(DefMI); continue; } @@ -275,7 +291,8 @@ void llvm::PHIElimination::LowerAtomicPHINode( FindCopyInsertPoint(opBlock, MBB, SrcReg); // Insert the copy. - TII->copyRegToReg(opBlock, InsertPos, IncomingReg, SrcReg, RC, RC); + if (!reusedIncoming && IncomingReg) + TII->copyRegToReg(opBlock, InsertPos, IncomingReg, SrcReg, RC, RC); // Now update live variable information if we have it. Otherwise we're done if (!LV) continue; @@ -292,32 +309,41 @@ void llvm::PHIElimination::LowerAtomicPHINode( // point later. // Is it used by any PHI instructions in this block? - bool ValueIsUsed = VRegPHIUseCount[BBVRegPair(&opBlock, SrcReg)] != 0; + bool ValueIsUsed = VRegPHIUseCount[BBVRegPair(opBlock.getNumber(), SrcReg)]; // Okay, if we now know that the value is not live out of the block, we can // add a kill marker in this block saying that it kills the incoming value! - if (!ValueIsUsed && !isLiveOut(SrcReg, opBlock, *LV)) { + if (!ValueIsUsed && !LV->isLiveOut(SrcReg, opBlock)) { // In our final twist, we have to decide which instruction kills the // register. In most cases this is the copy, however, the first // terminator instruction at the end of the block may also use the value. // In this case, we should mark *it* as being the killing block, not the // copy. - MachineBasicBlock::iterator KillInst = prior(InsertPos); + MachineBasicBlock::iterator KillInst; MachineBasicBlock::iterator Term = opBlock.getFirstTerminator(); - if (Term != opBlock.end()) { - if (Term->readsRegister(SrcReg)) - KillInst = Term; + if (Term != opBlock.end() && Term->readsRegister(SrcReg)) { + KillInst = Term; // Check that no other terminators use values. #ifndef NDEBUG - for (MachineBasicBlock::iterator TI = next(Term); TI != opBlock.end(); - ++TI) { + for (MachineBasicBlock::iterator TI = llvm::next(Term); + TI != opBlock.end(); ++TI) { assert(!TI->readsRegister(SrcReg) && "Terminator instructions cannot use virtual registers unless" "they are the first terminator in a block!"); } #endif + } else if (reusedIncoming || !IncomingReg) { + // We may have to rewind a bit if we didn't insert a copy this time. + KillInst = Term; + while (KillInst != opBlock.begin()) + if ((--KillInst)->readsRegister(SrcReg)) + break; + } else { + // We just inserted this copy. + KillInst = prior(InsertPos); } + assert(KillInst->readsRegister(SrcReg) && "Cannot find kill instruction"); // Finally, mark it killed. LV->addVirtualRegisterKilled(SrcReg, KillInst); @@ -328,9 +354,9 @@ void llvm::PHIElimination::LowerAtomicPHINode( } } - // Really delete the PHI instruction now! - MF.DeleteMachineInstr(MPhi); - ++NumAtomic; + // Really delete the PHI instruction now, if it is not in the LoweredPHIs map. + if (reusedIncoming || !IncomingReg) + MF.DeleteMachineInstr(MPhi); } /// analyzePHINodes - Gather information about the PHI nodes in here. In @@ -342,126 +368,75 @@ void llvm::PHIElimination::analyzePHINodes(const MachineFunction& Fn) { for (MachineFunction::const_iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) for (MachineBasicBlock::const_iterator BBI = I->begin(), BBE = I->end(); - BBI != BBE && BBI->getOpcode() == TargetInstrInfo::PHI; ++BBI) + BBI != BBE && BBI->isPHI(); ++BBI) for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) - ++VRegPHIUseCount[BBVRegPair(BBI->getOperand(i + 1).getMBB(), + ++VRegPHIUseCount[BBVRegPair(BBI->getOperand(i+1).getMBB()->getNumber(), BBI->getOperand(i).getReg())]; } bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF, - MachineBasicBlock &MBB) { - if (MBB.empty() || MBB.front().getOpcode() != TargetInstrInfo::PHI) + MachineBasicBlock &MBB, + LiveVariables &LV) { + if (MBB.empty() || !MBB.front().isPHI() || MBB.isLandingPad()) return false; // Quick exit for basic blocks without PHIs. - LiveVariables &LV = getAnalysis(); + for (MachineBasicBlock::const_iterator BBI = MBB.begin(), BBE = MBB.end(); - BBI != BBE && BBI->getOpcode() == TargetInstrInfo::PHI; ++BBI) { + BBI != BBE && BBI->isPHI(); ++BBI) { for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) { unsigned Reg = BBI->getOperand(i).getReg(); MachineBasicBlock *PreMBB = BBI->getOperand(i+1).getMBB(); // We break edges when registers are live out from the predecessor block // (not considering PHI nodes). If the register is live in to this block // anyway, we would gain nothing from splitting. - if (isLiveOut(Reg, *PreMBB, LV) && !isLiveIn(Reg, MBB, LV)) + if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) SplitCriticalEdge(PreMBB, &MBB); } } return true; } -bool llvm::PHIElimination::isLiveOut(unsigned Reg, const MachineBasicBlock &MBB, - LiveVariables &LV) { - LiveVariables::VarInfo &VI = LV.getVarInfo(Reg); - - // Loop over all of the successors of the basic block, checking to see if - // the value is either live in the block, or if it is killed in the block. - std::vector OpSuccBlocks; - for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(), - E = MBB.succ_end(); SI != E; ++SI) { - MachineBasicBlock *SuccMBB = *SI; - - // Is it alive in this successor? - unsigned SuccIdx = SuccMBB->getNumber(); - if (VI.AliveBlocks.test(SuccIdx)) - return true; - OpSuccBlocks.push_back(SuccMBB); - } - - // Check to see if this value is live because there is a use in a successor - // that kills it. - switch (OpSuccBlocks.size()) { - case 1: { - MachineBasicBlock *SuccMBB = OpSuccBlocks[0]; - for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i) - if (VI.Kills[i]->getParent() == SuccMBB) - return true; - break; - } - case 2: { - MachineBasicBlock *SuccMBB1 = OpSuccBlocks[0], *SuccMBB2 = OpSuccBlocks[1]; - for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i) - if (VI.Kills[i]->getParent() == SuccMBB1 || - VI.Kills[i]->getParent() == SuccMBB2) - return true; - break; - } - default: - std::sort(OpSuccBlocks.begin(), OpSuccBlocks.end()); - for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i) - if (std::binary_search(OpSuccBlocks.begin(), OpSuccBlocks.end(), - VI.Kills[i]->getParent())) - return true; - } - return false; -} - -bool llvm::PHIElimination::isLiveIn(unsigned Reg, const MachineBasicBlock &MBB, - LiveVariables &LV) { - LiveVariables::VarInfo &VI = LV.getVarInfo(Reg); - - if (VI.AliveBlocks.test(MBB.getNumber())) - return true; - - // defined in MBB? - const MachineInstr *Def = MRI->getVRegDef(Reg); - if (Def && Def->getParent() == &MBB) - return false; - - // killed in MBB? - return VI.findKill(&MBB); -} - MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A, MachineBasicBlock *B) { assert(A && B && "Missing MBB end point"); - ++NumSplits; MachineFunction *MF = A->getParent(); + + // We may need to update A's terminator, but we can't do that if AnalyzeBranch + // fails. If A uses a jump table, we won't touch it. + const TargetInstrInfo *TII = MF->getTarget().getInstrInfo(); + MachineBasicBlock *TBB = 0, *FBB = 0; + SmallVector Cond; + if (TII->AnalyzeBranch(*A, TBB, FBB, Cond)) + return NULL; + + ++NumSplits; + MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(); - MF->push_back(NMBB); - DEBUG(errs() << "PHIElimination splitting critical edge:" + MF->insert(llvm::next(MachineFunction::iterator(A)), NMBB); + DEBUG(dbgs() << "PHIElimination splitting critical edge:" " BB#" << A->getNumber() << " -- BB#" << NMBB->getNumber() << " -- BB#" << B->getNumber() << '\n'); A->ReplaceUsesOfBlockWith(B, NMBB); - // If A may fall through to B, we may have to insert a branch. - if (A->isLayoutSuccessor(B)) - A->updateTerminator(); + A->updateTerminator(); - // Insert unconditional "jump B" instruction in NMBB. + // Insert unconditional "jump B" instruction in NMBB if necessary. NMBB->addSuccessor(B); - SmallVector Cond; - MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond); + if (!NMBB->isLayoutSuccessor(B)) { + Cond.clear(); + MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond); + } // Fix PHI nodes in B so they refer to NMBB instead of A for (MachineBasicBlock::iterator i = B->begin(), e = B->end(); - i != e && i->getOpcode() == TargetInstrInfo::PHI; ++i) + i != e && i->isPHI(); ++i) for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2) if (i->getOperand(ni+1).getMBB() == A) i->getOperand(ni+1).setMBB(NMBB); if (LiveVariables *LV=getAnalysisIfAvailable()) - LV->addNewBlock(NMBB, A); + LV->addNewBlock(NMBB, A, B); if (MachineDominatorTree *MDT=getAnalysisIfAvailable()) MDT->addNewBlock(NMBB, A);