[RISCV] Reserve an emergency spill slot for the register scavenger when necessary
Although the register scavenger can often find a spare register, an emergency
spill slot is needed to guarantee success. Reserve this slot in cases where
the function is known to have a large stack (meaning the scavenger may be
needed when forming stack addresses).
llvm-svn: 322269
diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
index 85a354d..32ed896 100644
--- a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
@@ -18,6 +18,7 @@
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
using namespace llvm;
@@ -224,3 +225,21 @@
SavedRegs.set(RISCV::X1);
SavedRegs.set(RISCV::X8);
}
+
+void RISCVFrameLowering::processFunctionBeforeFrameFinalized(
+ MachineFunction &MF, RegScavenger *RS) const {
+ const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
+ MachineFrameInfo &MFI = MF.getFrameInfo();
+ const TargetRegisterClass *RC = &RISCV::GPRRegClass;
+ // estimateStackSize has been observed to under-estimate the final stack
+ // size, so give ourselves wiggle-room by checking for stack size
+ // representable an 11-bit signed field rather than 12-bits.
+ // FIXME: It may be possible to craft a function with a small stack that
+ // still needs an emergency spill slot for branch relaxation. This case
+ // would currently be missed.
+ if (!isInt<11>(MFI.estimateStackSize(MF))) {
+ int RegScavFI = MFI.CreateStackObject(
+ RegInfo->getSpillSize(*RC), RegInfo->getSpillAlignment(*RC), false);
+ RS->addScavengingFrameIndex(RegScavFI);
+ }
+}