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Fix coordination for using R4 in Thumb1 as a scratch for SP restore.

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The logic for reserving R4 for use as a scratch needs to match that for
actually using it. Also, it's not necessary for immediate <=508, so adjust
the value checked.

llvm-svn: 132934
This commit is contained in:
Jim Grosbach 2011-06-13 21:18:25 +00:00
parent 4fd206b70b
commit 3713c9ddfa
2 changed files with 9 additions and 4 deletions
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9
lib/Target/ARM/ARMFrameLowering.cpp
View File

@ -841,9 +841,14 @@ ARMFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
if (AFI->getVarArgsRegSaveSize() > 0)
MF.getRegInfo().setPhysRegUsed(ARM::LR);
// Spill R4 if Thumb1 epilogue has to restore SP from FP since
// Spill R4 if Thumb1 epilogue has to restore SP from FP. We don't know
// for sure what the stack size will be, but for this, an estimate is good
// enough. If there anything changes it, it'll be a spill, which implies
// we've used all the registers and so R4 is already used, so not marking
// it here will be OK.
// FIXME: It will be better just to find spare register here.
if (MFI->hasVarSizedObjects())
unsigned StackSize = estimateStackSize(MF);
if (MFI->hasVarSizedObjects() || StackSize > 508)
MF.getRegInfo().setPhysRegUsed(ARM::R4);
}

4
lib/Target/ARM/Thumb1FrameLowering.cpp
View File

@ -136,8 +136,8 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF) const {
BuildMI(MBB, MBBI, dl, TII.get(ARM::tADDrSPi), FramePtr)
.addFrameIndex(FramePtrSpillFI).addImm(0)
.setMIFlags(MachineInstr::FrameSetup);
if (NumBytes > 7)
// If offset is > 7 then sp cannot be adjusted in a single instruction,
if (NumBytes > 508)
// If offset is > 508 then sp cannot be adjusted in a single instruction,
// try restoring from fp instead.
AFI->setShouldRestoreSPFromFP(true);
}