X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FPHIElimination.cpp;h=8071b0a81a89bf0223fa6bf41b221ed7e334faf2;hb=d250329291dd9fe0d5f0e72e6cf1e287558a7cba;hp=07c4ef3f50948c3b13e38ebdb0b25ffa226c0777;hpb=d10fd9791c20fd8368fa0ce94b626b769c6c8ba0;p=oota-llvm.git diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp index 07c4ef3f509..8071b0a81a8 100644 --- a/lib/CodeGen/PHIElimination.cpp +++ b/lib/CodeGen/PHIElimination.cpp @@ -14,88 +14,79 @@ //===----------------------------------------------------------------------===// #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/MachineInstr.h" +#include "llvm/CodeGen/MachineInstrBuilder.h" #include "llvm/CodeGen/MachineRegisterInfo.h" -#include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" +#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/Statistic.h" #include "llvm/Support/Compiler.h" -#include #include +#include using namespace llvm; STATISTIC(NumAtomic, "Number of atomic phis lowered"); -//STATISTIC(NumSimple, "Number of simple phis lowered"); -namespace { - struct VISIBILITY_HIDDEN PNE : public MachineFunctionPass { - static char ID; // Pass identification, replacement for typeid - PNE() : MachineFunctionPass((intptr_t)&ID) {} +char PHIElimination::ID = 0; +static RegisterPass +X("phi-node-elimination", "Eliminate PHI nodes for register allocation"); - bool runOnMachineFunction(MachineFunction &Fn) { - analyzePHINodes(Fn); +const PassInfo *const llvm::PHIEliminationID = &X; - bool Changed = false; +void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesCFG(); + AU.addPreserved(); + AU.addPreservedID(MachineLoopInfoID); + AU.addPreservedID(MachineDominatorsID); + MachineFunctionPass::getAnalysisUsage(AU); +} - // 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); +bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &Fn) { + MRI = &Fn.getRegInfo(); - VRegPHIUseCount.clear(); - return Changed; - } + PHIDefs.clear(); + PHIKills.clear(); + analyzePHINodes(Fn); - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - AU.addPreserved(); - MachineFunctionPass::getAnalysisUsage(AU); - } + 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); - private: - /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions - /// in predecessor basic blocks. - /// - bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB); - void LowerAtomicPHINode(MachineBasicBlock &MBB, - 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"); + // Remove dead IMPLICIT_DEF instructions. + 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)) + DefMI->eraseFromParent(); + } + + ImpDefs.clear(); + VRegPHIUseCount.clear(); + return Changed; } -const PassInfo *llvm::PHIEliminationID = X.getPassInfo(); /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in /// predecessor basic blocks. /// -bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { +bool llvm::PHIElimination::EliminatePHINodes(MachineFunction &MF, + MachineBasicBlock &MBB) { if (MBB.empty() || MBB.front().getOpcode() != TargetInstrInfo::PHI) 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 = MBB.begin(); - while (AfterPHIsIt != MBB.end() && - AfterPHIsIt->getOpcode() == TargetInstrInfo::PHI) - ++AfterPHIsIt; // Skip over all of the PHI nodes... + MachineBasicBlock::iterator AfterPHIsIt = SkipPHIsAndLabels(MBB, MBB.begin()); while (MBB.front().getOpcode() == TargetInstrInfo::PHI) LowerAtomicPHINode(MBB, AfterPHIsIt); @@ -103,129 +94,190 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { 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; +/// isSourceDefinedByImplicitDef - Return true if all sources of the phi node +/// are implicit_def's. +static bool isSourceDefinedByImplicitDef(const MachineInstr *MPhi, + const MachineRegisterInfo *MRI) { + 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) + 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. +MachineBasicBlock::iterator +llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB, + 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())) + return MBB.getFirstTerminator(); + + // Discover any definition/uses in this basic block. + SmallPtrSet DefUsesInMBB; + for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg), + RE = MRI->reg_end(); RI != RE; ++RI) { + MachineInstr *DefUseMI = &*RI; + if (DefUseMI->getParent() == &MBB) + DefUsesInMBB.insert(DefUseMI); + } + + MachineBasicBlock::iterator InsertPoint; + if (DefUsesInMBB.empty()) { + // No def/uses. 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. + InsertPoint = *DefUsesInMBB.begin(); + ++InsertPoint; + } else { + // Insert the copy immediately after the last definition/use. + InsertPoint = MBB.end(); + while (!DefUsesInMBB.count(&*--InsertPoint)) {} + ++InsertPoint; + } + + // Make sure the copy goes after any phi nodes however. + return SkipPHIsAndLabels(MBB, InsertPoint); } /// 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) { +/// +void llvm::PHIElimination::LowerAtomicPHINode( + MachineBasicBlock &MBB, + 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 NumSrcs = (MPhi->getNumOperands() - 1) / 2; unsigned DestReg = MPhi->getOperand(0).getReg(); + bool isDead = MPhi->getOperand(0).isDead(); // Create a new register for the incoming PHI arguments. MachineFunction &MF = *MBB.getParent(); const TargetRegisterClass *RC = MF.getRegInfo().getRegClass(DestReg); - unsigned IncomingReg = MF.getRegInfo().createVirtualRegister(RC); + unsigned IncomingReg = 0; - // Insert a register to register copy in the top of the current block (but + // 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 // into the phi node destination. - // const TargetInstrInfo *TII = MF.getTarget().getInstrInfo(); - TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC); + if (isSourceDefinedByImplicitDef(MPhi, MRI)) + // 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); + else { + IncomingReg = MF.getRegInfo().createVirtualRegister(RC); + TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC); + } - // Update live variable information if there is any... - LiveVariables *LV = getAnalysisToUpdate(); + // 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); - // Increment use count of the newly created virtual register. - LV->getVarInfo(IncomingReg).NumUses++; + if (IncomingReg) { + // 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 - // for the VarInfo is not filled in. - // - LV->addVirtualRegisterKilled(IncomingReg, PHICopy); + // 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 + // for the VarInfo is not filled in. + LV->addVirtualRegisterKilled(IncomingReg, PHICopy); + } - // Since we are going to be deleting the PHI node, if it is the last use - // of any registers, or if the value itself is dead, we need to move this + // Since we are going to be deleting the PHI node, if it is the last use of + // any registers, or if the value itself is dead, we need to move this // information over to the new copy we just inserted. - // LV->removeVirtualRegistersKilled(MPhi); // If the result is dead, update LV. - if (LV->RegisterDefIsDead(MPhi, DestReg)) { + if (isDead) { LV->addVirtualRegisterDead(DestReg, PHICopy); - LV->removeVirtualRegistersDead(MPhi); + LV->removeVirtualRegisterDead(DestReg, 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. + // 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(), 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) { - unsigned SrcReg = MPhi->getOperand(i-1).getReg(); - assert(MRegisterInfo::isVirtualRegister(SrcReg) && + // Now loop over all of the incoming arguments, changing them to copy into the + // IncomingReg register in the corresponding predecessor basic block. + SmallPtrSet MBBsInsertedInto; + for (int i = NumSrcs - 1; i >= 0; --i) { + unsigned SrcReg = MPhi->getOperand(i*2+1).getReg(); + assert(TargetRegisterInfo::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).getMBB(); + // Get the MachineBasicBlock equivalent of the BasicBlock that is the source + // 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) { + ImpDefs.insert(DefMI); + continue; + } // 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. - if (!MBBsInsertedInto.insert(&opBlock).second) + // This can happen because PHI nodes may have multiple entries for the same + // basic block. + if (!MBBsInsertedInto.insert(&opBlock)) 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(); - + // 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); + // Insert the copy. - TII->copyRegToReg(opBlock, I, IncomingReg, SrcReg, RC, RC); + 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. + // 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); - 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. - // + // 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; @@ -239,8 +291,7 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, // Is it alive in this successor? unsigned SuccIdx = SuccMBB->getNumber(); - if (SuccIdx < InRegVI.AliveBlocks.size() && - InRegVI.AliveBlocks[SuccIdx]) { + if (InRegVI.AliveBlocks.test(SuccIdx)) { ValueIsLive = true; break; } @@ -282,48 +333,42 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, } } - // 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! + // 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 + // 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); + MachineBasicBlock::iterator KillInst = prior(InsertPos); + MachineBasicBlock::iterator Term = opBlock.getFirstTerminator(); + if (Term != opBlock.end()) { + if (Term->readsRegister(SrcReg)) + KillInst = Term; // Check that no other terminators use values. #ifndef NDEBUG - for (MachineBasicBlock::iterator TI = next(I); TI != opBlock.end(); + for (MachineBasicBlock::iterator TI = next(Term); TI != opBlock.end(); ++TI) { - assert(!InstructionUsesRegister(TI, SrcReg) && + assert(!TI->readsRegister(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; + InRegVI.AliveBlocks.reset(opBlockNum); } } // Really delete the PHI instruction now! - delete MPhi; + MF.DeleteMachineInstr(MPhi); ++NumAtomic; } @@ -332,7 +377,7 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, /// 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) { +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();