| //===-- PhiElimination.cpp - Eliminate PHI nodes by inserting copies ------===// | |
| // | |
| // The LLVM Compiler Infrastructure | |
| // | |
| // This file was developed by the LLVM research group and is distributed under | |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. | |
| // | |
| //===----------------------------------------------------------------------===// | |
| // | |
| // This pass eliminates machine instruction PHI nodes by inserting copy | |
| // instructions. This destroys SSA information, but is the desired input for | |
| // some register allocators. | |
| // | |
| //===----------------------------------------------------------------------===// | |
| #include "llvm/CodeGen/LiveVariables.h" | |
| #include "llvm/CodeGen/Passes.h" | |
| #include "llvm/CodeGen/MachineFunctionPass.h" | |
| #include "llvm/CodeGen/MachineInstr.h" | |
| #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" | |
| using namespace llvm; | |
| namespace { | |
| struct PNE : public MachineFunctionPass { | |
| bool runOnMachineFunction(MachineFunction &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); | |
| return Changed; | |
| } | |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { | |
| AU.addPreserved<LiveVariables>(); | |
| MachineFunctionPass::getAnalysisUsage(AU); | |
| } | |
| private: | |
| /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions | |
| /// in predecessor basic blocks. | |
| /// | |
| bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB); | |
| }; | |
| RegisterPass<PNE> 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 | |
| /// predecessor basic blocks. | |
| /// | |
| bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { | |
| if (MBB.empty() || MBB.front().getOpcode() != TargetInstrInfo::PHI) | |
| return false; // Quick exit for normal case... | |
| LiveVariables *LV = getAnalysisToUpdate<LiveVariables>(); | |
| const TargetInstrInfo &MII = *MF.getTarget().getInstrInfo(); | |
| const MRegisterInfo *RegInfo = MF.getTarget().getRegisterInfo(); | |
| // VRegPHIUseCount - Keep track of the number of times each virtual register | |
| // is used by PHI nodes in successors of this block. | |
| DenseMap<unsigned, VirtReg2IndexFunctor> 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). While we are scanning the PHIs, | |
| // populate the VRegPHIUseCount map. | |
| MachineBasicBlock::iterator AfterPHIsIt = MBB.begin(); | |
| while (AfterPHIsIt != MBB.end() && | |
| AfterPHIsIt->getOpcode() == TargetInstrInfo::PHI) | |
| ++AfterPHIsIt; // Skip over all of the PHI nodes... | |
| while (MBB.front().getOpcode() == TargetInstrInfo::PHI) { | |
| // Unlink the PHI node from the basic block, but don't delete the PHI yet. | |
| MachineInstr *MPhi = MBB.remove(MBB.begin()); | |
| assert(MRegisterInfo::isVirtualRegister(MPhi->getOperand(0).getReg()) && | |
| "PHI node doesn't write virt reg?"); | |
| unsigned DestReg = MPhi->getOperand(0).getReg(); | |
| // Create a new register for the incoming PHI arguments | |
| const TargetRegisterClass *RC = MF.getSSARegMap()->getRegClass(DestReg); | |
| unsigned IncomingReg = MF.getSSARegMap()->createVirtualRegister(RC); | |
| // Insert a register to register copy in the top of the current block (but | |
| // after any remaining phi nodes) which copies the new incoming register | |
| // into the phi node destination. | |
| // | |
| RegInfo->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC); | |
| // Update live variable information if there is any... | |
| if (LV) { | |
| MachineInstr *PHICopy = prior(AfterPHIsIt); | |
| // 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 | |
| // information over to the new copy we just inserted. | |
| // | |
| std::pair<LiveVariables::killed_iterator, LiveVariables::killed_iterator> | |
| RKs = LV->killed_range(MPhi); | |
| std::vector<std::pair<MachineInstr*, unsigned> > Range; | |
| if (RKs.first != RKs.second) // Delete the range. | |
| LV->removeVirtualRegistersKilled(RKs.first, RKs.second); | |
| RKs = LV->dead_range(MPhi); | |
| if (RKs.first != RKs.second) { | |
| // Works as above... | |
| Range.assign(RKs.first, RKs.second); | |
| LV->removeVirtualRegistersDead(RKs.first, RKs.second); | |
| for (unsigned i = 0, e = Range.size(); i != e; ++i) | |
| LV->addVirtualRegisterDead(Range[i].second, PHICopy); | |
| } | |
| } | |
| // 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; | |
| // Now loop over all of the incoming arguments, changing them to copy into | |
| // the IncomingReg register in the corresponding predecessor basic block. | |
| // | |
| for (int i = MPhi->getNumOperands() - 1; i >= 2; i-=2) { | |
| MachineOperand &opVal = MPhi->getOperand(i-1); | |
| // 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. | |
| // | |
| // 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! | |
| // | |
| 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; | |
| } | |
| } | |
| } | |
| 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]) { | |
| 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; | |
| } | |
| } | |
| } | |
| } | |
| // Really delete the PHI instruction now! | |
| delete MPhi; | |
| } | |
| return true; | |
| } |