X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FPHIElimination.cpp;h=371fb072b5b8572406c440db88777678e08b5fb1;hb=13c6a1740cb8877f10e202ee1442231e0c4a903a;hp=80c884dc9ae77f9c58265dd33f6b917e4385cc87;hpb=53a79aaae988d9dc9d12af8970f8b8fe58cc478d;p=oota-llvm.git diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp index 80c884dc9ae..371fb072b5b 100644 --- a/lib/CodeGen/PHIElimination.cpp +++ b/lib/CodeGen/PHIElimination.cpp @@ -13,6 +13,7 @@ // //===----------------------------------------------------------------------===// +#define DEBUG_TYPE "phielim" #include "llvm/CodeGen/LiveVariables.h" #include "llvm/CodeGen/Passes.h" #include "llvm/CodeGen/MachineFunctionPass.h" @@ -20,20 +21,31 @@ #include "llvm/CodeGen/SSARegMap.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" -#include "llvm/ADT/DenseMap.h" #include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Support/Compiler.h" #include +#include using namespace llvm; +STATISTIC(NumAtomic, "Number of atomic phis lowered"); +//STATISTIC(NumSimple, "Number of simple phis lowered"); + namespace { - struct PNE : public MachineFunctionPass { + struct VISIBILITY_HIDDEN PNE : public MachineFunctionPass { + static char ID; // Pass identification, replacement for typeid + PNE() : MachineFunctionPass((intptr_t)&ID) {} + bool runOnMachineFunction(MachineFunction &Fn) { + analyzePHINodes(Fn); + bool Changed = false; // 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); + VRegPHIUseCount.clear(); return Changed; } @@ -48,16 +60,27 @@ namespace { /// bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB); void LowerAtomicPHINode(MachineBasicBlock &MBB, - MachineBasicBlock::iterator AfterPHIsIt, - DenseMap &VUC, - unsigned BBIsSuccOfPreds); + MachineBasicBlock::iterator AfterPHIsIt); + + /// analyzePHINodes - Gather information about the PHI nodes in + /// here. In particular, we want to map the number of uses of a virtual + /// register which is used in a PHI node. We map that to the BB the + /// vreg is coming from. This is used later to determine when the vreg + /// is killed in the BB. + /// + void analyzePHINodes(const MachineFunction& Fn); + + typedef std::pair BBVRegPair; + typedef std::map VRegPHIUse; + + VRegPHIUse VRegPHIUseCount; }; + char PNE::ID = 0; RegisterPass X("phi-node-elimination", "Eliminate PHI nodes for register allocation"); } - const PassInfo *llvm::PHIEliminationID = X.getPassInfo(); /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in @@ -67,23 +90,6 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { if (MBB.empty() || MBB.front().getOpcode() != TargetInstrInfo::PHI) return false; // Quick exit for basic blocks without PHIs. - // VRegPHIUseCount - Keep track of the number of times each virtual register - // is used by PHI nodes in successors of this block. - DenseMap VRegPHIUseCount; - VRegPHIUseCount.grow(MF.getSSARegMap()->getLastVirtReg()); - - unsigned BBIsSuccOfPreds = 0; // Number of times MBB is a succ of preds - for (MachineBasicBlock::pred_iterator PI = MBB.pred_begin(), - E = MBB.pred_end(); PI != E; ++PI) - for (MachineBasicBlock::succ_iterator SI = (*PI)->succ_begin(), - E = (*PI)->succ_end(); SI != E; ++SI) { - BBIsSuccOfPreds += *SI == &MBB; - for (MachineBasicBlock::iterator BBI = (*SI)->begin(); BBI !=(*SI)->end() && - BBI->getOpcode() == TargetInstrInfo::PHI; ++BBI) - for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) - VRegPHIUseCount[BBI->getOperand(i).getReg()]++; - } - // 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 = MBB.begin(); @@ -91,26 +97,35 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { AfterPHIsIt->getOpcode() == TargetInstrInfo::PHI) ++AfterPHIsIt; // Skip over all of the PHI nodes... - while (MBB.front().getOpcode() == TargetInstrInfo::PHI) { - LowerAtomicPHINode(MBB, AfterPHIsIt, VRegPHIUseCount, BBIsSuccOfPreds); - } + while (MBB.front().getOpcode() == TargetInstrInfo::PHI) + LowerAtomicPHINode(MBB, AfterPHIsIt); + return true; } +/// InstructionUsesRegister - Return true if the specified machine instr has a +/// use of the specified register. +static bool InstructionUsesRegister(MachineInstr *MI, unsigned SrcReg) { + for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) + if (MI->getOperand(i).isRegister() && + MI->getOperand(i).getReg() == SrcReg && + MI->getOperand(i).isUse()) + return true; + return false; +} + /// LowerAtomicPHINode - Lower the PHI node at the top of the specified block, /// 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 PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, - MachineBasicBlock::iterator AfterPHIsIt, - DenseMap &VRegPHIUseCount, - unsigned BBIsSuccOfPreds) { + MachineBasicBlock::iterator AfterPHIsIt) { // Unlink the PHI node from the basic block, but don't delete the PHI yet. MachineInstr *MPhi = MBB.remove(MBB.begin()); unsigned DestReg = MPhi->getOperand(0).getReg(); - // Create a new register for the incoming PHI arguments/ + // Create a new register for the incoming PHI arguments. MachineFunction &MF = *MBB.getParent(); const TargetRegisterClass *RC = MF.getSSARegMap()->getRegClass(DestReg); unsigned IncomingReg = MF.getSSARegMap()->createVirtualRegister(RC); @@ -120,13 +135,16 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, // into the phi node destination. // const MRegisterInfo *RegInfo = MF.getTarget().getRegisterInfo(); - RegInfo->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC); + RegInfo->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC); // Update live variable information if there is any... LiveVariables *LV = getAnalysisToUpdate(); if (LV) { MachineInstr *PHICopy = prior(AfterPHIsIt); + // Increment use count of the newly created virtual register. + LV->getVarInfo(IncomingReg).NumUses++; + // Add information to LiveVariables to know that the incoming value is // killed. Note that because the value is defined in several places (once // each for each incoming block), the "def" block and instruction fields @@ -140,124 +158,188 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, // LV->removeVirtualRegistersKilled(MPhi); - std::pair - RKs = LV->dead_range(MPhi); - if (RKs.first != RKs.second) { - for (LiveVariables::killed_iterator I = RKs.first; I != RKs.second; ++I) - LV->addVirtualRegisterDead(*I, PHICopy); + // If the result is dead, update LV. + if (LV->RegisterDefIsDead(MPhi, DestReg)) { + LV->addVirtualRegisterDead(DestReg, PHICopy); LV->removeVirtualRegistersDead(MPhi); } + + // Realize that the destination register is defined by the PHI copy now, not + // the PHI itself. + LV->getVarInfo(DestReg).DefInst = PHICopy; + + LV->getVarInfo(IncomingReg).UsedBlocks[MBB.getNumber()] = true; } // Adjust the VRegPHIUseCount map to account for the removal of this PHI // node. for (unsigned i = 1; i != MPhi->getNumOperands(); i += 2) - VRegPHIUseCount[MPhi->getOperand(i).getReg()] -= BBIsSuccOfPreds; + --VRegPHIUseCount[BBVRegPair( + MPhi->getOperand(i + 1).getMachineBasicBlock(), + MPhi->getOperand(i).getReg())]; // Now loop over all of the incoming arguments, changing them to copy into // the IncomingReg register in the corresponding predecessor basic block. // + std::set MBBsInsertedInto; for (int i = MPhi->getNumOperands() - 1; i >= 2; i-=2) { - MachineOperand &opVal = MPhi->getOperand(i-1); + unsigned SrcReg = MPhi->getOperand(i-1).getReg(); + assert(MRegisterInfo::isVirtualRegister(SrcReg) && + "Machine PHI Operands must all be virtual registers!"); // Get the MachineBasicBlock equivalent of the BasicBlock that is the // source path the PHI. MachineBasicBlock &opBlock = *MPhi->getOperand(i).getMachineBasicBlock(); - MachineBasicBlock::iterator I = opBlock.getFirstTerminator(); - // Check to make sure we haven't already emitted the copy for this block. // This can happen because PHI nodes may have multiple entries for the - // same basic block. It doesn't matter which entry we use though, because - // all incoming values are guaranteed to be the same for a particular bb. + // same basic block. + if (!MBBsInsertedInto.insert(&opBlock).second) + continue; // If the copy has already been emitted, we're done. + + // Get an iterator pointing to the first terminator in the block (or end()). + // This is the point where we can insert a copy if we'd like to. + MachineBasicBlock::iterator I = opBlock.getFirstTerminator(); + + // Insert the copy. + RegInfo->copyRegToReg(opBlock, I, 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. // - // If we emitted a copy for this basic block already, it will be right - // where we want to insert one now. Just check for a definition of the - // register we are interested 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. // - bool HaveNotEmitted = true; - - if (I != opBlock.begin()) { - MachineBasicBlock::iterator PrevInst = prior(I); - for (unsigned i = 0, e = PrevInst->getNumOperands(); i != e; ++i) { - MachineOperand &MO = PrevInst->getOperand(i); - if (MO.isRegister() && MO.getReg() == IncomingReg) - if (MO.isDef()) { - HaveNotEmitted = false; - break; - } + LiveVariables::VarInfo &InRegVI = LV->getVarInfo(SrcReg); + InRegVI.UsedBlocks[opBlock.getNumber()] = true; + + // 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 (SuccIdx < InRegVI.AliveBlocks.size() && + InRegVI.AliveBlocks[SuccIdx]) { + ValueIsLive = true; + break; } + + OpSuccBlocks.push_back(SuccMBB); } - if (HaveNotEmitted) { // If the copy has not already been emitted, do it. - assert(MRegisterInfo::isVirtualRegister(opVal.getReg()) && - "Machine PHI Operands must all be virtual registers!"); - unsigned SrcReg = opVal.getReg(); - RegInfo->copyRegToReg(opBlock, I, IncomingReg, SrcReg, RC); - - // Now update live variable information if we have it. - if (LV) { - // 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. - // - bool ValueIsLive = false; - 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 (SuccIdx < InRegVI.AliveBlocks.size() && - InRegVI.AliveBlocks[SuccIdx]) { + // 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; } - - // Is it killed in this successor? - for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i) - if (InRegVI.Kills[i]->getParent() == SuccMBB) { - ValueIsLive = true; - break; - } - - // Is it used by any PHI instructions in this block? - if (!ValueIsLive) - ValueIsLive = VRegPHIUseCount[SrcReg] != 0; - } - - // Okay, if we now know that the value is not live out of the block, - // we can add a kill marker to the copy we inserted saying that it - // kills the incoming value! - // - if (!ValueIsLive) { - MachineBasicBlock::iterator Prev = prior(I); - LV->addVirtualRegisterKilled(SrcReg, Prev); - - // This vreg no longer lives all of the way through opBlock. - unsigned opBlockNum = opBlock.getNumber(); - if (opBlockNum < InRegVI.AliveBlocks.size()) - InRegVI.AliveBlocks[opBlockNum] = false; + 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; + } + } + } + + // 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) { + // 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. + bool FirstTerminatorUsesValue = false; + if (I != opBlock.end()) { + FirstTerminatorUsesValue = InstructionUsesRegister(I, SrcReg); + + // Check that no other terminators use values. +#ifndef NDEBUG + for (MachineBasicBlock::iterator TI = next(I); TI != opBlock.end(); + ++TI) { + assert(!InstructionUsesRegister(TI, SrcReg) && + "Terminator instructions cannot use virtual registers unless" + "they are the first terminator in a block!"); } +#endif } + + MachineBasicBlock::iterator KillInst; + if (!FirstTerminatorUsesValue) + KillInst = prior(I); + else + KillInst = I; + + // Finally, mark it killed. + LV->addVirtualRegisterKilled(SrcReg, KillInst); + + // This vreg no longer lives all of the way through opBlock. + unsigned opBlockNum = opBlock.getNumber(); + if (opBlockNum < InRegVI.AliveBlocks.size()) + InRegVI.AliveBlocks[opBlockNum] = false; } } // Really delete the PHI instruction now! delete MPhi; + ++NumAtomic; +} + +/// analyzePHINodes - Gather information about the PHI nodes in here. In +/// particular, we want to map the number of uses of a virtual register which is +/// used in a PHI node. We map that to the BB the vreg is coming from. This is +/// used later to determine when the vreg is killed in the BB. +/// +void PNE::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) + for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) + ++VRegPHIUseCount[BBVRegPair( + BBI->getOperand(i + 1).getMachineBasicBlock(), + BBI->getOperand(i).getReg())]; }