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If the only use of something is a DEBUG_VALUE, don't 

let that stop it from being deleted, and change the
DEBUG_VALUE value to undef.

llvm-svn: 94694
This commit is contained in:
Dale Johannesen 2010-01-27 22:12:36 +00:00
parent 77b108e17b
commit 6eb8e13236
1 changed files with 14 additions and 0 deletions
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14
llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
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@ -107,6 +107,20 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
MIE = MBB->rend(); MII != MIE; ) {
MachineInstr *MI = &*MII;
if (MI->getOpcode()==TargetInstrInfo::DEBUG_VALUE) {
// Don't delete the DEBUG_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_iterator I = MRI->use_begin(Reg);
assert(I != MRI->use_end());
if (++I == MRI->use_end())
// only one use, which must be this DEBUG_VALUE.
MI->getOperand(0).setReg(0U);
}
}
// If the instruction is dead, delete it!
if (isDead(MI)) {
DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);