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Clean up scavengeRegister() a bit to prefer available regs, which allows

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the simplification of frame index register scavenging to not have to check
for available registers directly and instead just let scavengeRegister()
handle it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107880 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jim Grosbach 2010-07-08 16:49:26 +00:00
parent 0bc25f4040
commit ed903d746d
2 changed files with 7 additions and 18 deletions
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16
lib/CodeGen/PrologEpilogInserter.cpp
View File

@ -885,21 +885,7 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
// Scavenge a new scratch register
CurrentVirtReg = Reg;
const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
BitVector Candidates(TRI->getNumRegs());
RS->getRegsAvailable(RC, Candidates);
// If there are any registers available, use the one that's
// unused for the longest after this instruction. That increases
// the ability to reuse the value.
if (Candidates.any()) {
MachineBasicBlock::iterator UMI;
CurrentScratchReg = RS->findSurvivorReg(I, Candidates, 25, UMI);
} else {
// No register is "free". Scavenge a register.
CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
}
CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
PrevValue = Value;
}
// replace this reference to the virtual register with the

9
lib/CodeGen/RegisterScavenging.cpp
View File

@ -339,13 +339,16 @@ unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
Candidates.reset(MO.getReg());
}
// Try to find a register that's unused if there is one, as then we won't
// have to spill.
if ((Candidates & RegsAvailable).any())
Candidates &= RegsAvailable;
// Find the register whose use is furthest away.
MachineBasicBlock::iterator UseMI;
unsigned SReg = findSurvivorReg(I, Candidates, 25, UseMI);
// If we found an unused register there is no reason to spill it. We have
// probably found a callee-saved register that has been saved in the
// prologue, but happens to be unused at this point.
// If we found an unused register there is no reason to spill it.
if (!isAliasUsed(SReg))
return SReg;