[RISCV] Implement isLoadFromStackSlot and isStoreToStackSlot

This causes some slight shuffling but no meaningful codegen differences on the 
corpus I used for testing, but it has a larger impact when combined with e.g. 
rematerialisation. Regardless, it makes sense to report as accurate 
target-specific information as possible.

llvm-svn: 330949

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -32,6 +32,55 @@ using namespace llvm;
 RISCVInstrInfo::RISCVInstrInfo()
     : RISCVGenInstrInfo(RISCV::ADJCALLSTACKDOWN, RISCV::ADJCALLSTACKUP) {}
 
+unsigned RISCVInstrInfo::isLoadFromStackSlot(const MachineInstr &MI,
+                                             int &FrameIndex) const {
+  switch (MI.getOpcode()) {
+  default:
+    return 0;
+  case RISCV::LB:
+  case RISCV::LBU:
+  case RISCV::LH:
+  case RISCV::LHU:
+  case RISCV::LW:
+  case RISCV::FLW:
+  case RISCV::LWU:
+  case RISCV::LD:
+  case RISCV::FLD:
+    break;
+  }
+
+  if (MI.getOperand(1).isFI() && MI.getOperand(2).isImm() &&
+      MI.getOperand(2).getImm() == 0) {
+    FrameIndex = MI.getOperand(1).getIndex();
+    return MI.getOperand(0).getReg();
+  }
+
+  return 0;
+}
+
+unsigned RISCVInstrInfo::isStoreToStackSlot(const MachineInstr &MI,
+                                            int &FrameIndex) const {
+  switch (MI.getOpcode()) {
+  default:
+    return 0;
+  case RISCV::SB:
+  case RISCV::SH:
+  case RISCV::SW:
+  case RISCV::FSW:
+  case RISCV::SD:
+  case RISCV::FSD:
+    break;
+  }
+
+  if (MI.getOperand(0).isFI() && MI.getOperand(1).isImm() &&
+      MI.getOperand(1).getImm() == 0) {
+    FrameIndex = MI.getOperand(0).getIndex();
+    return MI.getOperand(2).getReg();
+  }
+
+  return 0;
+}
+
 void RISCVInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator MBBI,
                                  const DebugLoc &DL, unsigned DstReg,

llvm/lib/Target/RISCV/RISCVInstrInfo.h

@@ -27,6 +27,11 @@ class RISCVInstrInfo : public RISCVGenInstrInfo {
 public:
   RISCVInstrInfo();
 
+  unsigned isLoadFromStackSlot(const MachineInstr &MI,
+                               int &FrameIndex) const override;
+  unsigned isStoreToStackSlot(const MachineInstr &MI,
+                              int &FrameIndex) const override;
+
   void copyPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
                    const DebugLoc &DL, unsigned DstReg, unsigned SrcReg,
                    bool KillSrc) const override;