X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FPHIElimination.cpp;h=ceba842970d3005e474a3bec805546065b7643c9;hb=ac6cecec189ba9689c42543c3106c02b96d788da;hp=37b7f45b1ade7f51c88772ae7c00b0527c5e02a5;hpb=fc5423d561bb7624bf328e3ed554efce6e296cbc;p=oota-llvm.git diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp index 37b7f45b1ad..ceba842970d 100644 --- a/lib/CodeGen/PHIElimination.cpp +++ b/lib/CodeGen/PHIElimination.cpp @@ -18,6 +18,7 @@ #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" @@ -72,13 +73,13 @@ namespace { // Defs of PHI sources which are implicit_def. SmallPtrSet ImpDefs; }; - - char PNE::ID = 0; - RegisterPass X("phi-node-elimination", - "Eliminate PHI nodes for register allocation"); } -const PassInfo *llvm::PHIEliminationID = X.getPassInfo(); +char PNE::ID = 0; +static RegisterPass +X("phi-node-elimination", "Eliminate PHI nodes for register allocation"); + +const PassInfo *const llvm::PHIEliminationID = &X; bool PNE::runOnMachineFunction(MachineFunction &Fn) { MRI = &Fn.getRegInfo(); @@ -96,7 +97,7 @@ bool PNE::runOnMachineFunction(MachineFunction &Fn) { E = ImpDefs.end(); I != E; ++I) { MachineInstr *DefMI = *I; unsigned DefReg = DefMI->getOperand(0).getReg(); - if (MRI->use_begin(DefReg) == MRI->use_end()) + if (MRI->use_empty(DefReg)) DefMI->eraseFromParent(); } @@ -126,122 +127,141 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) { return true; } +/// 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; +} + /// 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) { // 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, + 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... + // 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++; + 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 + LV->getVarInfo(IncomingReg).UsedBlocks[MBB.getNumber()] = true; + } + + // 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 (MPhi->registerDefIsDead(DestReg)) { + if (isDead) { LV->addVirtualRegisterDead(DestReg, PHICopy); - LV->removeVirtualRegistersDead(MPhi); + LV->removeVirtualRegisterDead(DestReg, MPhi); } - - 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. - // + // 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 = MPhi->getNumOperands() - 1; i >= 2; i-=2) { - unsigned SrcReg = MPhi->getOperand(i-1).getReg(); + 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!"); - // If source is defined by an implicit def, there is no need to insert - // a copy. + // 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; } - // 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(); // 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. + // 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. - // Find a safe location to insert the copy, this may be the first - // terminator in the block (or end()). + // Find a safe location to insert the copy, this may be the first terminator + // in the block (or end()). MachineBasicBlock::iterator InsertPos = opBlock.getFirstTerminator(); - + // Insert the copy. 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; @@ -298,12 +318,11 @@ 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. @@ -335,7 +354,7 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB, } // Really delete the PHI instruction now! - delete MPhi; + MF.DeleteMachineInstr(MPhi); ++NumAtomic; }