diff --git a/lib/CodeGen/LiveVariables.cpp b/lib/CodeGen/LiveVariables.cpp new file mode 100644 index 00000000000..d845f0646ff --- /dev/null +++ b/lib/CodeGen/LiveVariables.cpp @@ -0,0 +1,257 @@ +//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===// +// +// This file implements the LiveVariable analysis pass. +// +//===----------------------------------------------------------------------===// + +#include "llvm/CodeGen/LiveVariables.h" +#include "llvm/CodeGen/MachineInstr.h" +#include "llvm/Target/MachineInstrInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Support/CFG.h" +#include "Support/DepthFirstIterator.h" + +static RegisterAnalysis X("livevars", "Live Variable Analysis"); + +void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo, + const BasicBlock *BB) { + const std::pair &Info = BBMap.find(BB)->second; + MachineBasicBlock *MBB = Info.first; + unsigned BBNum = Info.second; + + // Check to see if this basic block is one of the killing blocks. If so, + // remove it... + for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i) + if (VRInfo.Kills[i].first == MBB) { + VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry + break; + } + + if (MBB == VRInfo.DefBlock) return; // Terminate recursion + + if (VRInfo.AliveBlocks.size() <= BBNum) + VRInfo.AliveBlocks.resize(BBNum+1); // Make space... + + if (VRInfo.AliveBlocks[BBNum]) + return; // We already know the block is live + + // Mark the variable known alive in this bb + VRInfo.AliveBlocks[BBNum] = true; + + for (pred_const_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + MarkVirtRegAliveInBlock(VRInfo, *PI); +} + +void LiveVariables::HandleVirtRegUse(VarInfo &VRInfo, MachineBasicBlock *MBB, + MachineInstr *MI) { + // Check to see if this basic block is already a kill block... + if (!VRInfo.Kills.empty() && VRInfo.Kills.back().first == MBB) { + // Yes, this register is killed in this basic block already. Increase the + // live range by updating the kill instruction. + VRInfo.Kills.back().second = MI; + return; + } + +#ifndef NDEBUG + for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i) + assert(VRInfo.Kills[i].first != MBB && "entry should be at end!"); +#endif + + assert(MBB != VRInfo.DefBlock && "Should have kill for defblock!"); + + // Add a new kill entry for this basic block. + VRInfo.Kills.push_back(std::make_pair(MBB, MI)); + + // Update all dominating blocks to mark them known live. + const BasicBlock *BB = MBB->getBasicBlock(); + for (pred_const_iterator PI = pred_begin(BB), E = pred_end(BB); + PI != E; ++PI) + MarkVirtRegAliveInBlock(VRInfo, *PI); +} + +void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr *MI) { + if (PhysRegInfo[Reg]) { + PhysRegInfo[Reg] = MI; + PhysRegUsed[Reg] = true; + } else if (const unsigned *AliasSet = RegInfo->getAliasSet(Reg)) { + for (; unsigned NReg = AliasSet[0]; ++AliasSet) + if (MachineInstr *LastUse = PhysRegInfo[NReg]) { + PhysRegInfo[NReg] = MI; + PhysRegUsed[NReg] = true; + } + } +} + +void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) { + // Does this kill a previous version of this register? + if (MachineInstr *LastUse = PhysRegInfo[Reg]) { + if (PhysRegUsed[Reg]) + RegistersKilled.insert(std::make_pair(LastUse, Reg)); + else + RegistersDead.insert(std::make_pair(LastUse, Reg)); + } else if (const unsigned *AliasSet = RegInfo->getAliasSet(Reg)) { + for (; unsigned NReg = AliasSet[0]; ++AliasSet) + if (MachineInstr *LastUse = PhysRegInfo[NReg]) { + if (PhysRegUsed[NReg]) + RegistersKilled.insert(std::make_pair(LastUse, NReg)); + else + RegistersDead.insert(std::make_pair(LastUse, NReg)); + PhysRegInfo[NReg] = 0; // Kill the aliased register + } + } + PhysRegInfo[Reg] = MI; + PhysRegUsed[Reg] = false; +} + +bool LiveVariables::runOnMachineFunction(MachineFunction &MF) { + // Build BBMap... + unsigned BBNum = 0; + for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) + BBMap[I->getBasicBlock()] = std::make_pair(I, BBNum++); + + // PhysRegInfo - Keep track of which instruction was the last use of a + // physical register. This is a purely local property, because all physical + // register references as presumed dead across basic blocks. + // + MachineInstr *PhysRegInfoA[MRegisterInfo::FirstVirtualRegister]; + bool PhysRegUsedA[MRegisterInfo::FirstVirtualRegister]; + std::fill(PhysRegInfoA, PhysRegInfoA+MRegisterInfo::FirstVirtualRegister, + (MachineInstr*)0); + PhysRegInfo = PhysRegInfoA; + PhysRegUsed = PhysRegUsedA; + + const TargetInstrInfo &TII = MF.getTarget().getInstrInfo(); + RegInfo = MF.getTarget().getRegisterInfo(); + + /// Get some space for a respectable number of registers... + VirtRegInfo.resize(64); + + // Calculate live variable information in depth first order on the CFG of the + // function. This guarantees that we will see the definition of a virtual + // register before its uses due to dominance properties of SSA (except for PHI + // nodes, which are treated as a special case). + // + const BasicBlock *Entry = MF.getFunction()->begin(); + for (df_iterator DFI = df_begin(Entry), E = df_end(Entry); + DFI != E; ++DFI) { + const BasicBlock *BB = *DFI; + std::pair &BBRec = BBMap.find(BB)->second; + MachineBasicBlock *MBB = BBRec.first; + unsigned BBNum = BBRec.second; + + // Loop over all of the instructions, processing them. + for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); + I != E; ++I) { + MachineInstr *MI = *I; + const TargetInstrDescriptor &MID = TII.get(MI->getOpcode()); + + // Process all of the operands of the instruction... + unsigned NumOperandsToProcess = MI->getNumOperands(); + + // Unless it is a PHI node. In this case, ONLY process the DEF, not any + // of the uses. They will be handled in other basic blocks. + if (MI->getOpcode() == TargetInstrInfo::PHI) + NumOperandsToProcess = 1; + + // Loop over implicit uses, using them. + if (const unsigned *ImplicitUses = MID.ImplicitUses) + for (unsigned i = 0; ImplicitUses[i]; ++i) + HandlePhysRegUse(ImplicitUses[i], MI); + + // Process all explicit uses... + for (unsigned i = 0; i != NumOperandsToProcess; ++i) { + MachineOperand &MO = MI->getOperand(i); + if (MO.opIsUse() || MO.opIsDefAndUse()) { + if (MO.isVirtualRegister() && !MO.getVRegValueOrNull()) { + unsigned RegIdx = MO.getReg()-MRegisterInfo::FirstVirtualRegister; + HandleVirtRegUse(getVarInfo(RegIdx), MBB, MI); + } else if (MO.isPhysicalRegister() && MO.getReg() != 0 + /// FIXME: This is a gross hack, due to us not being able to + /// say that some registers are defined on entry to the + /// function. 5 = ESP +&& MO.getReg() != 5 +) { + HandlePhysRegUse(MO.getReg(), MI); + } + } + } + + // Loop over implicit defs, defining them. + if (const unsigned *ImplicitDefs = MID.ImplicitDefs) + for (unsigned i = 0; ImplicitDefs[i]; ++i) + HandlePhysRegDef(ImplicitDefs[i], MI); + + // Process all explicit defs... + for (unsigned i = 0; i != NumOperandsToProcess; ++i) { + MachineOperand &MO = MI->getOperand(i); + if (MO.opIsDef() || MO.opIsDefAndUse()) { + if (MO.isVirtualRegister()) { + unsigned RegIdx = MO.getReg()-MRegisterInfo::FirstVirtualRegister; + VarInfo &VRInfo = getVarInfo(RegIdx); + + assert(VRInfo.DefBlock == 0 && "Variable multiply defined!"); + VRInfo.DefBlock = MBB; // Created here... + VRInfo.DefInst = MI; + VRInfo.Kills.push_back(std::make_pair(MBB, MI)); // Defaults to dead + } else if (MO.isPhysicalRegister() && MO.getReg() != 0 + /// FIXME: This is a gross hack, due to us not being able to + /// say that some registers are defined on entry to the + /// function. 5 = ESP +&& MO.getReg() != 5 +) { + HandlePhysRegDef(MO.getReg(), MI); + } + } + } + } + + // Handle any virtual assignments from PHI nodes which might be at the + // bottom of this basic block. We check all of our successor blocks to see + // if they have PHI nodes, and if so, we simulate an assignment at the end + // of the current block. + for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I){ + MachineBasicBlock *Succ = BBMap.find(*I)->second.first; + + // PHI nodes are guaranteed to be at the top of the block... + for (MachineBasicBlock::iterator I = Succ->begin(), E = Succ->end(); + I != E && (*I)->getOpcode() == TargetInstrInfo::PHI; ++I) { + for (unsigned i = 1; ; i += 2) + if ((*I)->getOperand(i+1).getMachineBasicBlock() == MBB) { + MachineOperand &MO = (*I)->getOperand(i); + if (!MO.getVRegValueOrNull()) { + unsigned RegIdx = MO.getReg()-MRegisterInfo::FirstVirtualRegister; + VarInfo &VRInfo = getVarInfo(RegIdx); + + // Only mark it alive only in the block we are representing... + MarkVirtRegAliveInBlock(VRInfo, BB); + break; // Found the PHI entry for this block... + } + } + } + } + + // Loop over PhysRegInfo, killing any registers that are available at the + // end of the basic block. This also resets the PhysRegInfo map. + for (unsigned i = 0, e = MRegisterInfo::FirstVirtualRegister; i != e; ++i) + if (PhysRegInfo[i]) + HandlePhysRegDef(i, 0); + } + + BBMap.clear(); + + // Convert the information we have gathered into VirtRegInfo and transform it + // into a form usable by RegistersKilled. + // + for (unsigned i = 0, e = VirtRegInfo.size(); i != e; ++i) + for (unsigned j = 0, e = VirtRegInfo[i].Kills.size(); j != e; ++j) { + if (VirtRegInfo[i].Kills[j].second == VirtRegInfo[i].DefInst) + RegistersDead.insert(std::make_pair(VirtRegInfo[i].Kills[j].second, + i + MRegisterInfo::FirstVirtualRegister)); + + else + RegistersKilled.insert(std::make_pair(VirtRegInfo[i].Kills[j].second, + i + MRegisterInfo::FirstVirtualRegister)); + } + + return false; +} diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp new file mode 100644 index 00000000000..ca243b8aae4 --- /dev/null +++ b/lib/CodeGen/PHIElimination.cpp @@ -0,0 +1,133 @@ +//===-- PhiElimination.cpp - Eliminate PHI nodes by inserting copies ------===// +// +// 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/MachineInstrInfo.h" +#include "llvm/Target/TargetMachine.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(); + MachineFunctionPass::getAnalysisUsage(AU); + } + + private: + /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions + /// in predecessor basic blocks. + /// + bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB); + }; + + RegisterPass 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.front()->getOpcode() != TargetInstrInfo::PHI) + return false; // Quick exit for normal case... + + LiveVariables *LV = getAnalysisToUpdate(); + 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 (by + // after any remaining phi nodes) which copies the new incoming register + // into the phi node destination. + // + MachineBasicBlock::iterator AfterPHIsIt = MBB.begin(); + while ((*AfterPHIsIt)->getOpcode() == TargetInstrInfo::PHI) ++AfterPHIsIt; + RegInfo->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC); + + // Add information to LiveVariables to know that the incoming value is dead + if (LV) LV->addVirtualRegisterKill(IncomingReg, *(AfterPHIsIt-1)); + + // Now loop over all of the incoming arguments turning them into copies 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(); + + // 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. + // + // Note that this is N^2 in the number of phi node entries, but since the + // # of entries is tiny, this is not a problem. + // + bool HaveNotEmitted = true; + for (int op = MI->getNumOperands() - 1; op != i; op -= 2) + if (&opBlock == MI->getOperand(op).getMachineBasicBlock()) { + HaveNotEmitted = false; + break; + } + + if (HaveNotEmitted) { + MachineBasicBlock::iterator I = opBlock.end()-1; + + // 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; + + assert(opVal.isVirtualRegister() && + "Machine PHI Operands must all be virtual registers!"); + RegInfo->copyRegToReg(opBlock, I, IncomingReg, opVal.getReg(), RC); + } + } + + // really delete the PHI instruction now! + delete MI; + } + + return true; +}