[llvm] MIPS: Implement isAsCheapAsAMove for addiu (PR #133273)

[YunQiang Su via llvm-commits]

https://github.com/wzssyqa created https://github.com/llvm/llvm-project/pull/133273

Set `addiu` as `isAsCheapAsAMove` only when the src register or imm is zero only.

If other cases are set `isAsCheapAsAMove`, MachineLICM will reject to hoist it.

>From a89cfa20c1b34351e34bfe3354595e52b07e117a Mon Sep 17 00:00:00 2001
From: YunQiang Su <syq at debian.org>
Date: Fri, 28 Mar 2025 00:20:12 +0800
Subject: [PATCH] MIPS: Implement isAsCheapAsAMove for addiu

Set `addiu` as `isAsCheapAsAMove` only when the src register or
imm is zero only.

If other cases are set `isAsCheapAsAMove`, MachineLICM will reject
to hoist it.
---
 llvm/lib/Target/Mips/MipsInstrInfo.cpp | 16 ++++++++++++++++
 llvm/lib/Target/Mips/MipsInstrInfo.h   |  2 ++
 2 files changed, 18 insertions(+)

diff --git a/llvm/lib/Target/Mips/MipsInstrInfo.cpp b/llvm/lib/Target/Mips/MipsInstrInfo.cpp
index d33652b4d2e3a..b81bb1186de72 100644
--- a/llvm/lib/Target/Mips/MipsInstrInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsInstrInfo.cpp
@@ -678,6 +678,22 @@ bool MipsInstrInfo::HasLoadDelaySlot(const MachineInstr &MI) const {
   }
 }
 
+bool MipsInstrInfo::isAsCheapAsAMove(const MachineInstr &MI) const {
+  const unsigned Opcode = MI.getOpcode();
+  switch (Opcode) {
+  default:
+    break;
+  case Mips::ADDiu:
+  case Mips::ADDiu_MM:
+  case Mips::DADDiu:
+    return ((MI.getOperand(2).isImm() && MI.getOperand(2).getImm() == 0) ||
+            (MI.getOperand(1).isReg() &&
+             (MI.getOperand(1).getReg() == Mips::ZERO ||
+              MI.getOperand(1).getReg() == Mips::ZERO_64)));
+  }
+  return MI.isAsCheapAsAMove();
+}
+
 /// Return the number of bytes of code the specified instruction may be.
 unsigned MipsInstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
   switch (MI.getOpcode()) {
diff --git a/llvm/lib/Target/Mips/MipsInstrInfo.h b/llvm/lib/Target/Mips/MipsInstrInfo.h
index 0fa8257089bc5..06964c0161b4b 100644
--- a/llvm/lib/Target/Mips/MipsInstrInfo.h
+++ b/llvm/lib/Target/Mips/MipsInstrInfo.h
@@ -113,6 +113,8 @@ class MipsInstrInfo : public MipsGenInstrInfo {
   /// Predicate to determine if an instruction has a load delay slot.
   bool HasLoadDelaySlot(const MachineInstr &MI) const;
 
+  bool isAsCheapAsAMove(const MachineInstr &MI) const override;
+
   /// Insert nop instruction when hazard condition is found
   void insertNoop(MachineBasicBlock &MBB,
                   MachineBasicBlock::iterator MI) const override;