X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FPHIElimination.cpp;h=f0057ce8ef8f3677008743012bb7bfa4963d65f3;hb=35a389344d21178ee280c2410401b2060b5b879c;hp=56dca086ef252163c04f285b7370ef8448f5eac3;hpb=20354634ebb64023d322919633f8bd348a63891d;p=oota-llvm.git diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp index 56dca086ef2..f0057ce8ef8 100644 --- a/lib/CodeGen/PHIElimination.cpp +++ b/lib/CodeGen/PHIElimination.cpp @@ -15,24 +15,28 @@ #define DEBUG_TYPE "phielim" #include "PHIElimination.h" -#include "llvm/BasicBlock.h" -#include "llvm/Instructions.h" #include "llvm/CodeGen/LiveVariables.h" #include "llvm/CodeGen/Passes.h" -#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineDominators.h" #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" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/Statistic.h" +#include "llvm/Support/CommandLine.h" #include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" #include #include using namespace llvm; STATISTIC(NumAtomic, "Number of atomic phis lowered"); +STATISTIC(NumSplits, "Number of critical edges split on demand"); +STATISTIC(NumReused, "Number of reused lowered phis"); char PHIElimination::ID = 0; static RegisterPass @@ -41,53 +45,63 @@ X("phi-node-elimination", "Eliminate PHI nodes for register allocation"); const PassInfo *const llvm::PHIEliminationID = &X; void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const { - AU.addPreserved(); - AU.addPreservedID(MachineLoopInfoID); - AU.addPreservedID(MachineDominatorsID); - MachineFunctionPass::getAnalysisUsage(AU); - } + AU.addPreserved(); + AU.addPreserved(); + // 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(); - analyzePHINodes(Fn); - bool Changed = false; + // Split critical edges to help the coalescer + if (LiveVariables *LV = getAnalysisIfAvailable()) + for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) + Changed |= SplitPHIEdges(Fn, *I, *LV); + + // Populate VRegPHIUseCount + analyzePHINodes(Fn); + // Eliminate PHI instructions by inserting copies into predecessor blocks. for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) 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; } - /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in /// predecessor basic blocks. /// 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; @@ -100,32 +114,34 @@ 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; } -// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg. -// This needs to be after any def or uses of SrcReg, but before any subsequent -// point where control flow might jump out of the basic block. +// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg +// when following the CFG edge to SuccMBB. This needs to be after any def of +// SrcReg, but before any subsequent point where control flow might jump out of +// the basic block. MachineBasicBlock::iterator llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB, + MachineBasicBlock &SuccMBB, unsigned SrcReg) { // Handle the trivial case trivially. if (MBB.empty()) return MBB.begin(); - // If this basic block does not contain an invoke, then control flow always - // reaches the end of it, so place the copy there. The logic below works in - // this case too, but is more expensive. - if (!isa(MBB.getBasicBlock()->getTerminator())) + // Usually, we just want to insert the copy before the first terminator + // instruction. However, for the edge going to a landing pad, we must insert + // the copy before the call/invoke instruction. + if (!SuccMBB.isLandingPad()) return MBB.getFirstTerminator(); - // Discover any definition/uses in this basic block. + // Discover any defs/uses in this basic block. SmallPtrSet DefUsesInMBB; for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg), - RE = MRI->reg_end(); RI != RE; ++RI) { + RE = MRI->reg_end(); RI != RE; ++RI) { MachineInstr *DefUseMI = &*RI; if (DefUseMI->getParent() == &MBB) DefUsesInMBB.insert(DefUseMI); @@ -133,14 +149,14 @@ llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertPoint; if (DefUsesInMBB.empty()) { - // No def/uses. Insert the copy at the start of the basic block. + // No defs. Insert the copy at the start of the basic block. InsertPoint = MBB.begin(); } else if (DefUsesInMBB.size() == 1) { - // Insert the copy immediately after the definition/use. + // Insert the copy immediately after the def/use. InsertPoint = *DefUsesInMBB.begin(); ++InsertPoint; } else { - // Insert the copy immediately after the last definition/use. + // Insert the copy immediately after the last def/use. InsertPoint = MBB.end(); while (!DefUsesInMBB.count(&*--InsertPoint)) {} ++InsertPoint; @@ -154,10 +170,11 @@ llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB, /// under the assuption that it needs to be lowered in a way that supports /// atomic execution of PHIs. This lowering method is always correct all of the /// time. -/// +/// 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()); @@ -169,6 +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 @@ -178,24 +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 @@ -218,7 +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 @@ -233,13 +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; } @@ -249,126 +284,79 @@ void llvm::PHIElimination::LowerAtomicPHINode( // basic block. if (!MBBsInsertedInto.insert(&opBlock)) continue; // If the copy has already been emitted, we're done. - + // Find a safe location to insert the copy, this may be the first terminator // in the block (or end()). - MachineBasicBlock::iterator InsertPos = FindCopyInsertPoint(opBlock, SrcReg); + MachineBasicBlock::iterator InsertPos = + 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; - + // We want to be able to insert a kill of the register if this PHI (aka, the // copy we just inserted) is the last use of the source value. Live // variable analysis conservatively handles this by saying that the value is // live until the end of the block the PHI entry lives in. If the value // really is dead at the PHI copy, there will be no successor blocks which // have the value live-in. - // - // Check to see if the copy is the last use, and if so, update the live - // variables information so that it knows the copy source instruction kills - // the incoming value. - LiveVariables::VarInfo &InRegVI = LV->getVarInfo(SrcReg); - - // 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. + // Also check to see if this register is in use by another PHI node which // has not yet been eliminated. If so, it will be killed at an appropriate // point later. // Is it used by any PHI instructions in this block? - bool ValueIsLive = VRegPHIUseCount[BBVRegPair(&opBlock, SrcReg)] != 0; - - std::vector OpSuccBlocks; - - // Otherwise, scan successors, including the BB the PHI node lives in. - for (MachineBasicBlock::succ_iterator SI = opBlock.succ_begin(), - E = opBlock.succ_end(); SI != E && !ValueIsLive; ++SI) { - MachineBasicBlock *SuccMBB = *SI; - - // Is it alive in this successor? - unsigned SuccIdx = SuccMBB->getNumber(); - if (InRegVI.AliveBlocks.test(SuccIdx)) { - ValueIsLive = true; - break; - } - - OpSuccBlocks.push_back(SuccMBB); - } - - // Check to see if this value is live because there is a use in a successor - // that kills it. - if (!ValueIsLive) { - switch (OpSuccBlocks.size()) { - case 1: { - MachineBasicBlock *MBB = OpSuccBlocks[0]; - for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i) - if (InRegVI.Kills[i]->getParent() == MBB) { - ValueIsLive = true; - break; - } - break; - } - case 2: { - MachineBasicBlock *MBB1 = OpSuccBlocks[0], *MBB2 = OpSuccBlocks[1]; - for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i) - if (InRegVI.Kills[i]->getParent() == MBB1 || - InRegVI.Kills[i]->getParent() == MBB2) { - ValueIsLive = true; - break; - } - break; - } - default: - std::sort(OpSuccBlocks.begin(), OpSuccBlocks.end()); - for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i) - if (std::binary_search(OpSuccBlocks.begin(), OpSuccBlocks.end(), - InRegVI.Kills[i]->getParent())) { - ValueIsLive = true; - break; - } - } - } + 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 (!ValueIsLive) { + 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); // This vreg no longer lives all of the way through opBlock. unsigned opBlockNum = opBlock.getNumber(); - InRegVI.AliveBlocks.reset(opBlockNum); + LV->getVarInfo(SrcReg).AliveBlocks.reset(opBlockNum); } } - - // 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 @@ -380,8 +368,78 @@ 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, + LiveVariables &LV) { + if (MBB.empty() || !MBB.front().isPHI() || MBB.isLandingPad()) + return false; // Quick exit for basic blocks without PHIs. + + for (MachineBasicBlock::const_iterator BBI = MBB.begin(), BBE = MBB.end(); + 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 (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) + SplitCriticalEdge(PreMBB, &MBB); + } + } + return true; +} + +MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A, + MachineBasicBlock *B) { + assert(A && B && "Missing MBB end point"); + + 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->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); + A->updateTerminator(); + + // Insert unconditional "jump B" instruction in NMBB if necessary. + NMBB->addSuccessor(B); + 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->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, B); + + if (MachineDominatorTree *MDT=getAnalysisIfAvailable()) + MDT->addNewBlock(NMBB, A); + + return NMBB; +}