[AArch64] Break the dependency between FP and SP when possible.
When the SP in not changed because of realignment/VLAs etc., we restore the SP
by using the previous value of SP and not the FP. Breaking the dependency will
help in cases when the epilog of a callee is close to the epilog of the caller;
for then "sub sp, fp, #" depends on the load restoring the FP in the epilog of
the callee.
http://reviews.llvm.org/D18060
Patch by Aditya Kumar and Evandro Menezes.
llvm-svn: 263458
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 9560048..1cdb525 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -396,6 +396,7 @@
BuildMI(MBB, MBBI, DL, TII->get(AArch64::ANDXri), AArch64::SP)
.addReg(scratchSPReg, RegState::Kill)
.addImm(andMaskEncoded);
+ AFI->setStackRealigned(true);
}
// If we need a base pointer, set it up here. It's whatever the value of the
@@ -607,10 +608,13 @@
// FIXME: Rather than doing the math here, we should instead just use
// non-post-indexed loads for the restores if we aren't actually going to
// be able to save any instructions.
- if (NumBytes || MFI->hasVarSizedObjects())
+ if (MFI->hasVarSizedObjects() || AFI->isStackRealigned())
emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::FP,
-AFI->getCalleeSavedStackSize() + 16, TII,
MachineInstr::FrameDestroy);
+ else if (NumBytes)
+ emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP, NumBytes, TII,
+ MachineInstr::FrameDestroy);
// This must be placed after the callee-save restore code because that code
// assumes the SP is at the same location as it was after the callee-save save