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[RISCV] Allow spilling to unused Zcmp Stack #125959

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Merged
merged 1 commit into from
Feb 7, 2025
Merged

[RISCV] Allow spilling to unused Zcmp Stack #125959

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11 changes: 8 additions & 3 deletions llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1847,11 +1847,16 @@ bool RISCVFrameLowering::assignCalleeSavedSpillSlots(
MFI.setStackID(FrameIdx, TargetStackID::ScalableVector);
}

// Allocate a fixed object that covers the full push or libcall size.
if (RVFI->isPushable(MF)) {
if (int64_t PushSize = RVFI->getRVPushStackSize())
MFI.CreateFixedSpillStackObject(PushSize, -PushSize);
// Allocate a fixed object that covers all the registers that are pushed.
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@topperc topperc Feb 6, 2025 •
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I'm a bit curious if this object is needed at all. We already created an object for each register. The save/restore needs an object to cover the missing registers, but maybe push/pop doesn't?

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We might not have created an object for each register. See void @spill_x10() in llvm/test/CodeGen/RISCV/push-pop-popret.ll, where from what I can tell, we only have an object for s10 and s11. For the same reasons as with save/restore, we cannot clobber the stack used by the other (lower-numbered) callee-saved registers, because we definitely restore into them with pop

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ok thanks.

if (unsigned PushedRegs = RVFI->getRVPushRegs()) {
int64_t PushedRegsBytes =
static_cast<int64_t>(PushedRegs) * (STI.getXLen() / 8);
MFI.CreateFixedSpillStackObject(PushedRegsBytes, -PushedRegsBytes);
}
} else if (int LibCallRegs = getLibCallID(MF, CSI) + 1) {
// Allocate a fixed object that covers all of the stack allocated by the
// libcall.
int64_t LibCallFrameSize =
alignTo((STI.getXLen() / 8) * LibCallRegs, getStackAlign());
MFI.CreateFixedSpillStackObject(LibCallFrameSize, -LibCallFrameSize);
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