| //===-- 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/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/SSARegMap.h" |
| #include "llvm/CodeGen/LiveVariables.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/Target/TargetMachine.h" |
| #include "llvm/Support/CFG.h" |
| |
| 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); |
| |
| //std::cerr << "AFTER PHI NODE ELIM:\n"; |
| //Fn.dump(); |
| 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 *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(); |
| |
| while (MBB.front()->getOpcode() == TargetInstrInfo::PHI) { |
| MachineInstr *MI = MBB.front(); |
| // Unlink the PHI node from the basic block... but don't delete the PHI yet |
| MBB.erase(MBB.begin()); |
| |
| assert(MI->getOperand(0).isVirtualRegister() && |
| "PHI node doesn't write virt reg?"); |
| |
| unsigned DestReg = MI->getOperand(0).getAllocatedRegNum(); |
| |
| // 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. |
| // |
| MachineBasicBlock::iterator AfterPHIsIt = MBB.begin(); |
| while (AfterPHIsIt != MBB.end() && |
| (*AfterPHIsIt)->getOpcode() == TargetInstrInfo::PHI) |
| ++AfterPHIsIt; // Skip over all of the PHI nodes... |
| RegInfo->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC); |
| |
| // Update live variable information if there is any... |
| if (LV) { |
| MachineInstr *PHICopy = *(AfterPHIsIt-1); |
| |
| // 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, &MBB, 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(MI); |
| std::vector<std::pair<MachineInstr*, unsigned> > Range; |
| if (RKs.first != RKs.second) { |
| // Copy the range into a vector... |
| Range.assign(RKs.first, RKs.second); |
| |
| // Delete the range... |
| LV->removeVirtualRegistersKilled(RKs.first, RKs.second); |
| |
| // Add all of the kills back, which will update the appropriate info... |
| for (unsigned i = 0, e = Range.size(); i != e; ++i) |
| LV->addVirtualRegisterKilled(Range[i].second, &MBB, PHICopy); |
| } |
| |
| RKs = LV->dead_range(MI); |
| 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, &MBB, PHICopy); |
| } |
| } |
| |
| // 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 = MI->getNumOperands() - 1; i >= 2; i-=2) { |
| MachineOperand &opVal = MI->getOperand(i-1); |
| |
| // Get the MachineBasicBlock equivalent of the BasicBlock that is the |
| // source path the PHI. |
| MachineBasicBlock &opBlock = *MI->getOperand(i).getMachineBasicBlock(); |
| |
| // Figure out where to insert the copy, which is at the end of the |
| // predecessor basic block, but before any terminator/branch |
| // instructions... |
| MachineBasicBlock::iterator I = opBlock.end(); |
| if (I != opBlock.begin()) { // Handle empty blocks |
| --I; |
| // must backtrack over ALL the branches in the previous block |
| while (MII.isTerminatorInstr((*I)->getOpcode()) && |
| I != opBlock.begin()) |
| --I; |
| |
| // move back to the first branch instruction so new instructions |
| // are inserted right in front of it and not in front of a non-branch |
| if (!MII.isTerminatorInstr((*I)->getOpcode())) |
| ++I; |
| } |
| |
| // 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()) { |
| MachineInstr *PrevInst = *(I-1); |
| for (unsigned i = 0, e = PrevInst->getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = PrevInst->getOperand(i); |
| if (MO.isVirtualRegister() && MO.getReg() == IncomingReg) |
| if (MO.opIsDefOnly() || MO.opIsDefAndUse()) { |
| HaveNotEmitted = false; |
| break; |
| } |
| } |
| } |
| |
| if (HaveNotEmitted) { // If the copy has not already been emitted, do it. |
| assert(opVal.isVirtualRegister() && |
| "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; |
| const BasicBlock *BB = opBlock.getBasicBlock(); |
| for (succ_const_iterator SI = succ_begin(BB), E = succ_end(BB); |
| SI != E && !ValueIsLive; ++SI) { |
| const std::pair<MachineBasicBlock*, unsigned> & |
| SuccInfo = LV->getBasicBlockInfo(*SI); |
| |
| // Is it alive in this successor? |
| unsigned SuccIdx = SuccInfo.second; |
| if (SuccIdx < InRegVI.AliveBlocks.size() && |
| InRegVI.AliveBlocks[SuccIdx]) { |
| ValueIsLive = true; |
| break; |
| } |
| |
| // Is it killed in this successor? |
| MachineBasicBlock *MBB = SuccInfo.first; |
| for (unsigned i = 0, e = InRegVI.Kills.size(); i != e; ++i) |
| if (InRegVI.Kills[i].first == MBB) { |
| ValueIsLive = true; |
| break; |
| } |
| |
| // Is it used by any PHI instructions in this block? |
| if (ValueIsLive) break; |
| |
| // Loop over all of the PHIs in this successor, checking to see if |
| // the register is being used... |
| for (MachineBasicBlock::iterator BBI = MBB->begin(), E=MBB->end(); |
| BBI != E && (*BBI)->getOpcode() == TargetInstrInfo::PHI; |
| ++BBI) |
| for (unsigned i = 1, e = (*BBI)->getNumOperands(); i < e; i += 2) |
| if ((*BBI)->getOperand(i).getReg() == SrcReg) { |
| ValueIsLive = true; |
| break; |
| } |
| } |
| |
| // 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) |
| LV->addVirtualRegisterKilled(SrcReg, &opBlock, *(I-1)); |
| } |
| } |
| } |
| |
| // really delete the PHI instruction now! |
| delete MI; |
| } |
| |
| return true; |
| } |
