From 01addf8046dd54b95f20631190caa9f2a8d684bc Mon Sep 17 00:00:00 2001
From: Alex Richardson <Alexander.Richardson@cl.cam.ac.uk>
Date: Mon, 21 Sep 2020 08:59:22 +0100
Subject: [PATCH] [RISC-V] Implement RISCVInstrInfo::isCopyInstrImpl()

This does not result in changes for any of the current tests, but it might
improve debug information in some cases.

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D86522
---
 lib/Target/RISCV/RISCVInstrInfo.cpp | 24 +++++++++++++++++++++++-
 lib/Target/RISCV/RISCVInstrInfo.h   |  3 +++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/lib/Target/RISCV/RISCVInstrInfo.cpp b/lib/Target/RISCV/RISCVInstrInfo.cpp
index 249264d1945..57ce933075a 100644
--- a/lib/Target/RISCV/RISCVInstrInfo.cpp
+++ b/lib/Target/RISCV/RISCVInstrInfo.cpp
@@ -517,7 +517,7 @@ bool RISCVInstrInfo::isAsCheapAsAMove(const MachineInstr &MI) const {
     break;
   case RISCV::FSGNJ_D:
   case RISCV::FSGNJ_S:
-    // The canonical floatig-point move is fsgnj rd, rs, rs.
+    // The canonical floating-point move is fsgnj rd, rs, rs.
     return MI.getOperand(1).isReg() && MI.getOperand(2).isReg() &&
            MI.getOperand(1).getReg() == MI.getOperand(2).getReg();
   case RISCV::ADDI:
@@ -530,6 +530,28 @@ bool RISCVInstrInfo::isAsCheapAsAMove(const MachineInstr &MI) const {
   return MI.isAsCheapAsAMove();
 }
 
+Optional<DestSourcePair>
+RISCVInstrInfo::isCopyInstrImpl(const MachineInstr &MI) const {
+  if (MI.isMoveReg())
+    return DestSourcePair{MI.getOperand(0), MI.getOperand(1)};
+  switch (MI.getOpcode()) {
+  default:
+    break;
+  case RISCV::ADDI:
+    if (MI.getOperand(2).isImm() && MI.getOperand(2).getImm() == 0)
+      return DestSourcePair{MI.getOperand(0), MI.getOperand(1)};
+    break;
+  case RISCV::FSGNJ_D:
+  case RISCV::FSGNJ_S:
+    // The canonical floating-point move is fsgnj rd, rs, rs.
+    if (MI.getOperand(1).isReg() && MI.getOperand(2).isReg() &&
+        MI.getOperand(1).getReg() == MI.getOperand(2).getReg())
+      return DestSourcePair{MI.getOperand(0), MI.getOperand(1)};
+    break;
+  }
+  return None;
+}
+
 bool RISCVInstrInfo::verifyInstruction(const MachineInstr &MI,
                                        StringRef &ErrInfo) const {
   const MCInstrInfo *MCII = STI.getInstrInfo();
diff --git a/lib/Target/RISCV/RISCVInstrInfo.h b/lib/Target/RISCV/RISCVInstrInfo.h
index cd8b6d5fba5..180a3e88bc8 100644
--- a/lib/Target/RISCV/RISCVInstrInfo.h
+++ b/lib/Target/RISCV/RISCVInstrInfo.h
@@ -83,6 +83,9 @@ public:
 
   bool isAsCheapAsAMove(const MachineInstr &MI) const override;
 
+  Optional<DestSourcePair>
+  isCopyInstrImpl(const MachineInstr &MI) const override;
+
   bool verifyInstruction(const MachineInstr &MI,
                          StringRef &ErrInfo) const override;