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In Thumb2 mode, lower frame indix references to:

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add <rd>, sp, #<imm8>
ldr <rd>, [sp, #<imm8>]
When the offset from sp is multiple of 4 and in range of 0-1020.
This saves code size by utilizing 16-bit instructions.

rdar://9321541


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129971 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2011-04-22 01:42:52 +00:00
parent d8a1624122
commit db6cbe1ff1
3 changed files with 36 additions and 9 deletions
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19
lib/Target/ARM/ARMFrameLowering.cpp
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@ -445,8 +445,7 @@ ARMFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
int
ARMFrameLowering::ResolveFrameIndexReference(const MachineFunction &MF,
int FI,
unsigned &FrameReg,
int FI, unsigned &FrameReg,
int SPAdj) const {
const MachineFrameInfo *MFI = MF.getFrameInfo();
const ARMBaseRegisterInfo *RegInfo =
@ -490,19 +489,23 @@ ARMFrameLowering::ResolveFrameIndexReference(const MachineFunction &MF,
return FPOffset;
} else if (MFI->hasVarSizedObjects()) {
assert(RegInfo->hasBasePointer(MF) && "missing base pointer!");
// Try to use the frame pointer if we can, else use the base pointer
// since it's available. This is handy for the emergency spill slot, in
// particular.
if (AFI->isThumb2Function()) {
// Try to use the frame pointer if we can, else use the base pointer
// since it's available. This is handy for the emergency spill slot, in
// particular.
if (FPOffset >= -255 && FPOffset < 0) {
FrameReg = RegInfo->getFrameRegister(MF);
return FPOffset;
}
} else
FrameReg = RegInfo->getBaseRegister();
}
} else if (AFI->isThumb2Function()) {
// Use add <rd>, sp, #<imm8>
// ldr <rd>, [sp, #<imm8>]
// if at all possible to save space.
if (Offset >= 0 && (Offset & 3) == 0 && Offset <= 1020)
return Offset;
// In Thumb2 mode, the negative offset is very limited. Try to avoid
// out of range references.
// out of range references. ldr <rt>,[<rn>, #-<imm8>]
if (FPOffset >= -255 && FPOffset < 0) {
FrameReg = RegInfo->getFrameRegister(MF);
return FPOffset;