[RISCV][NFC] Combine RISCVOptWInstrs::stripWSuffixes and appendWSuffixes into canonicalizeWSuffixes (#149710)

This refactor was suggested in
<#144703>.

I have checked for unexpected changes by comparing builds of
llvm-test-suite with/without this refactor, including with preferWInst
force enabled.

Author: asb

llvm/lib/Target/RISCV/RISCVOptWInstrs.cpp

@@ -69,10 +69,9 @@ class RISCVOptWInstrs : public MachineFunctionPass {
   bool runOnMachineFunction(MachineFunction &MF) override;
   bool removeSExtWInstrs(MachineFunction &MF, const RISCVInstrInfo &TII,
                          const RISCVSubtarget &ST, MachineRegisterInfo &MRI);
-  bool stripWSuffixes(MachineFunction &MF, const RISCVInstrInfo &TII,
-                      const RISCVSubtarget &ST, MachineRegisterInfo &MRI);
-  bool appendWSuffixes(MachineFunction &MF, const RISCVInstrInfo &TII,
-                       const RISCVSubtarget &ST, MachineRegisterInfo &MRI);
+  bool canonicalizeWSuffixes(MachineFunction &MF, const RISCVInstrInfo &TII,
+                             const RISCVSubtarget &ST,
+                             MachineRegisterInfo &MRI);
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
@@ -723,51 +722,38 @@ bool RISCVOptWInstrs::removeSExtWInstrs(MachineFunction &MF,
   return MadeChange;
 }
 
-bool RISCVOptWInstrs::stripWSuffixes(MachineFunction &MF,
-                                     const RISCVInstrInfo &TII,
-                                     const RISCVSubtarget &ST,
-                                     MachineRegisterInfo &MRI) {
+// Strips or adds W suffixes to eligible instructions depending on the
+// subtarget preferences.
+bool RISCVOptWInstrs::canonicalizeWSuffixes(MachineFunction &MF,
+                                            const RISCVInstrInfo &TII,
+                                            const RISCVSubtarget &ST,
+                                            MachineRegisterInfo &MRI) {
+  bool ShouldStripW = !(DisableStripWSuffix || ST.preferWInst());
+  bool ShouldPreferW = ST.preferWInst();
   bool MadeChange = false;
-  for (MachineBasicBlock &MBB : MF) {
-    for (MachineInstr &MI : MBB) {
-      unsigned Opc;
-      // clang-format off
-      switch (MI.getOpcode()) {
-      default:
-        continue;
-      case RISCV::ADDW:  Opc = RISCV::ADD;  break;
-      case RISCV::ADDIW: Opc = RISCV::ADDI; break;
-      case RISCV::MULW:  Opc = RISCV::MUL;  break;
-      case RISCV::SLLIW: Opc = RISCV::SLLI; break;
-      case RISCV::SUBW:  Opc = RISCV::SUB;  break;
-      }
-      // clang-format on
 
-      if (hasAllWUsers(MI, ST, MRI)) {
-        LLVM_DEBUG(dbgs() << "Replacing " << MI);
-        MI.setDesc(TII.get(Opc));
-        LLVM_DEBUG(dbgs() << "     with " << MI);
-        ++NumTransformedToNonWInstrs;
-        MadeChange = true;
-      }
-    }
-  }
-
-  return MadeChange;
-}
-
-bool RISCVOptWInstrs::appendWSuffixes(MachineFunction &MF,
-                                      const RISCVInstrInfo &TII,
-                                      const RISCVSubtarget &ST,
-                                      MachineRegisterInfo &MRI) {
-  bool MadeChange = false;
   for (MachineBasicBlock &MBB : MF) {
     for (MachineInstr &MI : MBB) {
-      unsigned WOpc;
-      // TODO: Add more?
+      std::optional<unsigned> WOpc;
+      std::optional<unsigned> NonWOpc;
       switch (MI.getOpcode()) {
       default:
         continue;
+      case RISCV::ADDW:
+        NonWOpc = RISCV::ADD;
+        break;
+      case RISCV::ADDIW:
+        NonWOpc = RISCV::ADDI;
+        break;
+      case RISCV::MULW:
+        NonWOpc = RISCV::MUL;
+        break;
+      case RISCV::SLLIW:
+        NonWOpc = RISCV::SLLI;
+        break;
+      case RISCV::SUBW:
+        NonWOpc = RISCV::SUB;
+        break;
       case RISCV::ADD:
         WOpc = RISCV::ADDW;
         break;
@@ -781,7 +767,7 @@ bool RISCVOptWInstrs::appendWSuffixes(MachineFunction &MF,
         WOpc = RISCV::MULW;
         break;
       case RISCV::SLLI:
-        // SLLIW reads the lowest 5 bits, while SLLI reads lowest 6 bits
+        // SLLIW reads the lowest 5 bits, while SLLI reads lowest 6 bits.
         if (MI.getOperand(2).getImm() >= 32)
           continue;
         WOpc = RISCV::SLLIW;
@@ -792,19 +778,27 @@ bool RISCVOptWInstrs::appendWSuffixes(MachineFunction &MF,
         break;
       }
 
-      if (hasAllWUsers(MI, ST, MRI)) {
+      if (ShouldStripW && NonWOpc.has_value() && hasAllWUsers(MI, ST, MRI)) {
         LLVM_DEBUG(dbgs() << "Replacing " << MI);
-        MI.setDesc(TII.get(WOpc));
+        MI.setDesc(TII.get(NonWOpc.value()));
+        LLVM_DEBUG(dbgs() << "     with " << MI);
+        ++NumTransformedToNonWInstrs;
+        MadeChange = true;
+        continue;
+      }
+      if (ShouldPreferW && WOpc.has_value() && hasAllWUsers(MI, ST, MRI)) {
+        LLVM_DEBUG(dbgs() << "Replacing " << MI);
+        MI.setDesc(TII.get(WOpc.value()));
         MI.clearFlag(MachineInstr::MIFlag::NoSWrap);
         MI.clearFlag(MachineInstr::MIFlag::NoUWrap);
         MI.clearFlag(MachineInstr::MIFlag::IsExact);
         LLVM_DEBUG(dbgs() << "     with " << MI);
         ++NumTransformedToWInstrs;
         MadeChange = true;
+        continue;
       }
     }
   }
-
   return MadeChange;
 }
 
@@ -821,12 +815,6 @@ bool RISCVOptWInstrs::runOnMachineFunction(MachineFunction &MF) {
 
   bool MadeChange = false;
   MadeChange |= removeSExtWInstrs(MF, TII, ST, MRI);
-
-  if (!(DisableStripWSuffix || ST.preferWInst()))
-    MadeChange |= stripWSuffixes(MF, TII, ST, MRI);
-
-  if (ST.preferWInst())
-    MadeChange |= appendWSuffixes(MF, TII, ST, MRI);
-
+  MadeChange |= canonicalizeWSuffixes(MF, TII, ST, MRI);
   return MadeChange;
 }