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Better handling of dead super registers in LiveVariables. We used to do this:

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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
This commit is contained in:
Jakob Stoklund Olesen 2010-03-05 21:49:17 +00:00
parent a76e816844
commit 53e000bac3
2 changed files with 22 additions and 22 deletions
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42
lib/CodeGen/LiveVariables.cpp
View File

@ -365,27 +365,7 @@ bool LiveVariables::HandlePhysRegKill(unsigned Reg, MachineInstr *MI) {
}
}
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 @@ bool LiveVariables::HandlePhysRegKill(unsigned Reg, MachineInstr *MI) {
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;

2
test/CodeGen/X86/2008-08-05-SpillerBug.ll
View File

@ -1,4 +1,4 @@
; RUN: llc < %s -mtriple=i386-apple-darwin -disable-fp-elim -stats |& grep asm-printer | grep 58
; RUN: llc < %s -mtriple=i386-apple-darwin -disable-fp-elim -stats |& grep asm-printer | grep 55
; PR2568
@g_3 = external global i16 ; <i16*> [#uses=1]