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Handle <undef> operands in TwoAddressInstructionPass.

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When the source register to a 2-addr instruction is undefined, there is
no need to attempt any transformations - simply replace the source
register with the destination register.

This also comes up when lowering IMPLICIT_DEF instructions - make sure
the <undef> flag is moved to the new partial register def operand:

  %vreg8<def> = INSERT_SUBREG %vreg9<undef>, %vreg0<kill>, sub_16bit
rewrite undef:
  %vreg8<def> = INSERT_SUBREG %vreg8<undef>, %vreg0<kill>, sub_16bit
convert to:
  %vreg8:sub_16bit<def,read-undef> = COPY %vreg0<kill>

llvm-svn: 159120
This commit is contained in:
Jakob Stoklund Olesen 2012-06-25 03:27:12 +00:00
parent 76fcb51532
commit 8fc784fec2
1 changed files with 31 additions and 12 deletions
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21
lib/CodeGen/TwoAddressInstructionPass.cpp
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@ -1456,6 +1456,19 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
"two address instruction invalid");
unsigned regB = mi->getOperand(SrcIdx).getReg();
// Deal with <undef> uses immediately - simply rewrite the src operand.
if (mi->getOperand(SrcIdx).isUndef()) {
unsigned DstReg = mi->getOperand(DstIdx).getReg();
// Constrain the DstReg register class if required.
if (TargetRegisterInfo::isVirtualRegister(DstReg))
if (const TargetRegisterClass *RC = TII->getRegClass(MCID, SrcIdx,
TRI, MF))
MRI->constrainRegClass(DstReg, RC);
mi->getOperand(SrcIdx).setReg(DstReg);
DEBUG(dbgs() << "\t\trewrite undef:\t" << *mi);
continue;
}
TiedOperands[regB].push_back(std::make_pair(SrcIdx, DstIdx));
}
@ -1609,6 +1622,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
MadeChange = true;
DEBUG(dbgs() << "\t\trewrite to:\t" << *mi);
}
// Rewrite INSERT_SUBREG as COPY now that we no longer need SSA form.
if (mi->isInsertSubreg()) {
@ -1618,11 +1632,11 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
mi->RemoveOperand(3);
assert(mi->getOperand(0).getSubReg() == 0 && "Unexpected subreg idx");
mi->getOperand(0).setSubReg(SubIdx);
mi->getOperand(0).setIsUndef(mi->getOperand(1).isUndef());
mi->RemoveOperand(1);
mi->setDesc(TII->get(TargetOpcode::COPY));
DEBUG(dbgs() << "\t\tconvert to:\t" << *mi);
}
}
// Clear TiedOperands here instead of at the top of the loop
// since most instructions do not have tied operands.
@ -1846,6 +1860,11 @@ bool TwoAddressInstructionPass::EliminateRegSequences() {
SmallVector<unsigned, 4> RealSrcs;
SmallSet<unsigned, 4> Seen;
for (unsigned i = 1, e = MI->getNumOperands(); i < e; i += 2) {
// Nothing needs to be inserted for <undef> operands.
if (MI->getOperand(i).isUndef()) {
MI->getOperand(i).setReg(0);
continue;
}
unsigned SrcReg = MI->getOperand(i).getReg();
unsigned SrcSubIdx = MI->getOperand(i).getSubReg();
unsigned SubIdx = MI->getOperand(i+1).getImm();