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Track local physical register liveness. This is not the most
efficient implementation possible, but it's pretty simple and good enough for the time being. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56504 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -42,16 +42,38 @@ FunctionPass *llvm::createDeadMachineInstructionElimPass() {
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bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
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bool AnyChanges = false;
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const TargetRegisterInfo &TRI = *MF.getTarget().getRegisterInfo();
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const MachineRegisterInfo &MRI = MF.getRegInfo();
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const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
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BitVector LivePhysRegs;
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bool SawStore = true;
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// Compute a bitvector to represent all non-allocatable physregs.
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BitVector NonAllocatableRegs = TRI.getAllocatableSet(MF);
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NonAllocatableRegs.flip();
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// Loop over all instructions in all blocks, from bottom to top, so that it's
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// more likely that chains of dependent but ultimately dead instructions will
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// be cleaned up.
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for (MachineFunction::reverse_iterator I = MF.rbegin(), E = MF.rend();
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I != E; ++I) {
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MachineBasicBlock *MBB = &*I;
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// Start out assuming that all non-allocatable registers are live
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// out of this block.
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LivePhysRegs = NonAllocatableRegs;
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// Also add any explicit live-out physregs for this block.
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if (!MBB->empty() && MBB->back().getDesc().isReturn())
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for (MachineRegisterInfo::liveout_iterator LOI = MRI.liveout_begin(),
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LOE = MRI.liveout_end(); LOI != LOE; ++LOI) {
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unsigned Reg = *LOI;
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if (TargetRegisterInfo::isPhysicalRegister(Reg))
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LivePhysRegs.set(Reg);
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}
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// Now scan the instructions and delete dead ones, tracking physreg
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// liveness as we go.
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for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
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MIE = MBB->rend(); MII != MIE; ) {
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MachineInstr *MI = &*MII;
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@ -64,9 +86,8 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isRegister() && MO.isDef()) {
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unsigned Reg = MO.getReg();
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if ((!MO.isImplicit() &&
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TargetRegisterInfo::isPhysicalRegister(Reg)) ||
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!MRI.use_empty(Reg)) {
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if (TargetRegisterInfo::isPhysicalRegister(Reg) ?
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LivePhysRegs[Reg] : !MRI.use_empty(Reg)) {
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// This def has a use. Don't delete the instruction!
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AllDefsDead = false;
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break;
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@ -90,6 +111,35 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
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continue;
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}
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}
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// Record the physreg defs.
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isRegister() && MO.isDef()) {
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unsigned Reg = MO.getReg();
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if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
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LivePhysRegs.reset(Reg);
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for (const unsigned *AliasSet = TRI.getAliasSet(Reg);
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*AliasSet; ++AliasSet)
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LivePhysRegs.reset(*AliasSet);
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}
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}
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}
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// Record the physreg uses, after the defs, in case a physreg is
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// both defined and used in the same instruction.
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isRegister() && MO.isUse()) {
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unsigned Reg = MO.getReg();
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if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
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LivePhysRegs.set(Reg);
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for (const unsigned *AliasSet = TRI.getAliasSet(Reg);
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*AliasSet; ++AliasSet)
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LivePhysRegs.set(*AliasSet);
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}
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}
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}
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// We didn't delete the current instruction, so increment MII to
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// the next one.
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++MII;
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