Better handling of dead super registers in LiveVariables. We used to do this:
CALL ... %RAX<imp-def>
... [not using %RAX]
%EAX = ..., %RAX<imp-use, kill>
RET %EAX<imp-use,kill>
Now we do this:
CALL ... %RAX<imp-def, dead>
... [not using %RAX]
%EAX = ...
RET %EAX<imp-use,kill>
By not artificially keeping %RAX alive, we lower register pressure a bit.
The correct number of instructions for 2008-08-05-SpillerBug.ll is obviously
55, anybody can see that. Sheesh.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97838 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveVariables.cpp b/lib/CodeGen/LiveVariables.cpp
index 68c8539..519990e 100644
--- a/lib/CodeGen/LiveVariables.cpp
+++ b/lib/CodeGen/LiveVariables.cpp
@@ -365,27 +365,7 @@
}
}
- if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI) {
- if (LastPartDef)
- // The last partial def kills the register.
- LastPartDef->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
- true/*IsImp*/, true/*IsKill*/));
- else {
- MachineOperand *MO =
- LastRefOrPartRef->findRegisterDefOperand(Reg, false, TRI);
- bool NeedEC = MO->isEarlyClobber() && MO->getReg() != Reg;
- // If the last reference is the last def, then it's not used at all.
- // That is, unless we are currently processing the last reference itself.
- LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
- if (NeedEC) {
- // If we are adding a subreg def and the superreg def is marked early
- // clobber, add an early clobber marker to the subreg def.
- MO = LastRefOrPartRef->findRegisterDefOperand(Reg);
- if (MO)
- MO->setIsEarlyClobber();
- }
- }
- } else if (!PhysRegUse[Reg]) {
+ if (!PhysRegUse[Reg]) {
// Partial uses. Mark register def dead and add implicit def of
// sub-registers which are used.
// EAX<dead> = op AL<imp-def>
@@ -419,6 +399,26 @@
for (const unsigned *SS = TRI->getSubRegisters(SubReg); *SS; ++SS)
PartUses.erase(*SS);
}
+ } else if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI) {
+ if (LastPartDef)
+ // The last partial def kills the register.
+ LastPartDef->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
+ true/*IsImp*/, true/*IsKill*/));
+ else {
+ MachineOperand *MO =
+ LastRefOrPartRef->findRegisterDefOperand(Reg, false, TRI);
+ bool NeedEC = MO->isEarlyClobber() && MO->getReg() != Reg;
+ // If the last reference is the last def, then it's not used at all.
+ // That is, unless we are currently processing the last reference itself.
+ LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
+ if (NeedEC) {
+ // If we are adding a subreg def and the superreg def is marked early
+ // clobber, add an early clobber marker to the subreg def.
+ MO = LastRefOrPartRef->findRegisterDefOperand(Reg);
+ if (MO)
+ MO->setIsEarlyClobber();
+ }
+ }
} else
LastRefOrPartRef->addRegisterKilled(Reg, TRI, true);
return true;