In Thumb2 mode, lower frame indix references to:
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
diff --git a/lib/Target/ARM/ARMFrameLowering.cpp b/lib/Target/ARM/ARMFrameLowering.cpp
index c99259d..e2e95d4 100644
--- a/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/lib/Target/ARM/ARMFrameLowering.cpp
@@ -445,8 +445,7 @@
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 @@
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;