//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
-#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/Support/Compiler.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
-#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+
using namespace llvm;
+#define DEBUG_TYPE "codegen-dce"
+
+STATISTIC(NumDeletes, "Number of dead instructions deleted");
+
namespace {
- class VISIBILITY_HIDDEN DeadMachineInstructionElim :
- public MachineFunctionPass {
- virtual bool runOnMachineFunction(MachineFunction &MF);
-
+ class DeadMachineInstructionElim : public MachineFunctionPass {
+ bool runOnMachineFunction(MachineFunction &MF) override;
+
+ const TargetRegisterInfo *TRI;
+ const MachineRegisterInfo *MRI;
+ const TargetInstrInfo *TII;
+ BitVector LivePhysRegs;
+
public:
static char ID; // Pass identification, replacement for typeid
- DeadMachineInstructionElim() : MachineFunctionPass(&ID) {}
+ DeadMachineInstructionElim() : MachineFunctionPass(ID) {
+ initializeDeadMachineInstructionElimPass(*PassRegistry::getPassRegistry());
+ }
+
+ private:
+ bool isDead(const MachineInstr *MI) const;
};
}
char DeadMachineInstructionElim::ID = 0;
+char &llvm::DeadMachineInstructionElimID = DeadMachineInstructionElim::ID;
+
+INITIALIZE_PASS(DeadMachineInstructionElim, "dead-mi-elimination",
+ "Remove dead machine instructions", false, false)
-static RegisterPass<DeadMachineInstructionElim>
-Y("dead-mi-elimination",
- "Remove dead machine instructions");
+bool DeadMachineInstructionElim::isDead(const MachineInstr *MI) const {
+ // Technically speaking inline asm without side effects and no defs can still
+ // be deleted. But there is so much bad inline asm code out there, we should
+ // let them be.
+ if (MI->isInlineAsm())
+ return false;
-FunctionPass *llvm::createDeadMachineInstructionElimPass() {
- return new DeadMachineInstructionElim();
+ // Don't delete frame allocation labels.
+ if (MI->getOpcode() == TargetOpcode::LOCAL_ESCAPE)
+ return false;
+
+ // Don't delete instructions with side effects.
+ bool SawStore = false;
+ if (!MI->isSafeToMove(nullptr, SawStore) && !MI->isPHI())
+ return false;
+
+ // Examine each operand.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (MO.isReg() && MO.isDef()) {
+ unsigned Reg = MO.getReg();
+ if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
+ // Don't delete live physreg defs, or any reserved register defs.
+ if (LivePhysRegs.test(Reg) || MRI->isReserved(Reg))
+ return false;
+ } else {
+ if (!MRI->use_nodbg_empty(Reg))
+ // This def has a non-debug use. Don't delete the instruction!
+ return false;
+ }
+ }
+ }
+
+ // If there are no defs with uses, the instruction is dead.
+ return true;
}
bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
+ if (skipOptnoneFunction(*MF.getFunction()))
+ return false;
+
bool AnyChanges = false;
- const MachineRegisterInfo &MRI = MF.getRegInfo();
- const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
- bool SawStore = true;
+ MRI = &MF.getRegInfo();
+ TRI = MF.getSubtarget().getRegisterInfo();
+ TII = MF.getSubtarget().getInstrInfo();
// Loop over all instructions in all blocks, from bottom to top, so that it's
// more likely that chains of dependent but ultimately dead instructions will
// be cleaned up.
- for (MachineFunction::reverse_iterator I = MF.rbegin(), E = MF.rend();
- I != E; ++I) {
- MachineBasicBlock *MBB = &*I;
- for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
- MIE = MBB->rend(); MII != MIE; ) {
+ for (MachineBasicBlock &MBB : make_range(MF.rbegin(), MF.rend())) {
+ // Start out assuming that reserved registers are live out of this block.
+ LivePhysRegs = MRI->getReservedRegs();
+
+ // Add live-ins from sucessors to LivePhysRegs. Normally, physregs are not
+ // live across blocks, but some targets (x86) can have flags live out of a
+ // block.
+ for (MachineBasicBlock::succ_iterator S = MBB.succ_begin(),
+ E = MBB.succ_end(); S != E; S++)
+ for (unsigned LI : (*S)->liveins())
+ LivePhysRegs.set(LI);
+
+ // Now scan the instructions and delete dead ones, tracking physreg
+ // liveness as we go.
+ for (MachineBasicBlock::reverse_iterator MII = MBB.rbegin(),
+ MIE = MBB.rend(); MII != MIE; ) {
MachineInstr *MI = &*MII;
- // Don't delete instructions with side effects.
- if (MI->isSafeToMove(&TII, SawStore)) {
- // Examine each operand.
- bool AllDefsDead = true;
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI->getOperand(i);
- if (MO.isRegister() && MO.isDef()) {
- unsigned Reg = MO.getReg();
- if (TargetRegisterInfo::isPhysicalRegister(Reg) ||
- !MRI.use_empty(Reg)) {
- // This def has a use. Don't delete the instruction!
- AllDefsDead = false;
- break;
- }
+ // If the instruction is dead, delete it!
+ if (isDead(MI)) {
+ DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);
+ // It is possible that some DBG_VALUE instructions refer to this
+ // instruction. They get marked as undef and will be deleted
+ // in the live debug variable analysis.
+ MI->eraseFromParentAndMarkDBGValuesForRemoval();
+ AnyChanges = true;
+ ++NumDeletes;
+ MIE = MBB.rend();
+ // MII is now pointing to the next instruction to process,
+ // so don't increment it.
+ continue;
+ }
+
+ // Record the physreg defs.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (MO.isReg() && MO.isDef()) {
+ unsigned Reg = MO.getReg();
+ if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
+ // Check the subreg set, not the alias set, because a def
+ // of a super-register may still be partially live after
+ // this def.
+ for (MCSubRegIterator SR(Reg, TRI,/*IncludeSelf=*/true);
+ SR.isValid(); ++SR)
+ LivePhysRegs.reset(*SR);
}
+ } else if (MO.isRegMask()) {
+ // Register mask of preserved registers. All clobbers are dead.
+ LivePhysRegs.clearBitsNotInMask(MO.getRegMask());
}
-
- // If there are no defs with uses, the instruction is dead.
- if (AllDefsDead) {
- // Clear out the operands to take the registers out of their
- // use chains.
- while (unsigned Num = MI->getNumOperands())
- MI->RemoveOperand(Num-1);
-
- // Delete the actual instruction.
- AnyChanges = true;
- MI->eraseFromParent();
- MIE = MBB->rend();
- // MII is now pointing to the next instruction to process,
- // so don't increment it.
- continue;
+ }
+ // Record the physreg uses, after the defs, in case a physreg is
+ // both defined and used in the same instruction.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (MO.isReg() && MO.isUse()) {
+ unsigned Reg = MO.getReg();
+ if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ LivePhysRegs.set(*AI);
+ }
}
}
+
// We didn't delete the current instruction, so increment MII to
// the next one.
++MII;
}
}
+ LivePhysRegs.clear();
return AnyChanges;
}
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