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Rewrite handling of DBG_VALUE; previous algorithm

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didn't handle
X =
Y<dead> = use X
DBG_VALUE(X)
I was hoping to avoid this approach as it's slower,
but I don't think it can be done.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95996 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2010-02-12 18:40:17 +00:00
parent c3b6ffc431
commit 2d1ec73d94
1 changed files with 24 additions and 16 deletions
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40
lib/CodeGen/DeadMachineInstructionElim.cpp
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@ -64,8 +64,8 @@ bool DeadMachineInstructionElim::isDead(const MachineInstr *MI) const {
if (MO.isReg() && MO.isDef()) {
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isPhysicalRegister(Reg) ?
LivePhysRegs[Reg] : !MRI->use_empty(Reg)) {
// This def has a use. Don't delete the instruction!
LivePhysRegs[Reg] : !MRI->use_nodbg_empty(Reg)) {
// This def has a non-debug use. Don't delete the instruction!
return false;
}
}
@ -111,23 +111,31 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
MIE = MBB->rend(); MII != MIE; ) {
MachineInstr *MI = &*MII;
if (MI->isDebugValue()) {
// Don't delete the DBG_VALUE itself, but if its Value operand is
// a vreg and this is the only use, substitute an undef operand;
// the former operand will then be deleted normally.
if (MI->getNumOperands()==3 && MI->getOperand(0).isReg()) {
unsigned Reg = MI->getOperand(0).getReg();
MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(Reg);
if (I == MRI->use_nodbg_end())
// All uses are DBG_VALUEs. Nullify this one; if we find
// others later we will nullify them then.
MI->getOperand(0).setReg(0U);
}
}
// 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. Examine each def operand for such references;
// if found, mark the DBG_VALUE as undef (but don't delete it).
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
MachineRegisterInfo::use_iterator nextI;
for (MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg),
E = MRI->use_end(); I!=E; I=nextI) {
nextI = llvm::next(I); // I is invalidated by the setReg
MachineOperand& Use = I.getOperand();
MachineInstr *UseMI = Use.getParent();
if (UseMI==MI)
continue;
assert(Use.isDebug());
UseMI->getOperand(0).setReg(0U);
}
}
AnyChanges = true;
MI->eraseFromParent();
++NumDeletes;