[RISCV] Move FixableDef handling out of isSignExtendingOpW.

We have two layers of opcode checks. The first is in
isSignExtendingOpW. If that returns false, a second switch is used
for looking through nodes by adding them to the worklist.

Move the FixableDef handling to the second switch. This simplies
the interface of isSignExtendingOpW and makes that function more
accurate to its name.

llvm/lib/Target/RISCV/RISCVSExtWRemoval.cpp

@@ -220,13 +220,9 @@ static bool hasAllWUsers(const MachineInstr &OrigMI, MachineRegisterInfo &MRI) {
 
 // This function returns true if the machine instruction always outputs a value
 // where bits 63:32 match bit 31.
-// Alternatively, if the instruction can be converted to W variant
-// (e.g. ADD->ADDW) and all of its uses only use the lower word of its output,
-// then return true and add the instr to FixableDef to be convereted later
 // TODO: Allocate a bit in TSFlags for the W instructions?
 // TODO: Add other W instructions.
-static bool isSignExtendingOpW(MachineInstr &MI, MachineRegisterInfo &MRI,
-                               SmallPtrSetImpl<MachineInstr *> &FixableDef) {
+static bool isSignExtendingOpW(MachineInstr &MI, MachineRegisterInfo &MRI) {
   switch (MI.getOpcode()) {
   case RISCV::LUI:
   case RISCV::LW:
@@ -286,13 +282,8 @@ static bool isSignExtendingOpW(MachineInstr &MI, MachineRegisterInfo &MRI,
     return MI.getOperand(2).getImm() > 32;
   // The LI pattern ADDI rd, X0, imm is sign extended.
   case RISCV::ADDI:
-    if (MI.getOperand(1).isReg() && MI.getOperand(1).getReg() == RISCV::X0)
+    return MI.getOperand(1).isReg() && MI.getOperand(1).getReg() == RISCV::X0;
       return true;
-    if (hasAllWUsers(MI, MRI)) {
-      // transform to ADDIW
-      FixableDef.insert(&MI);
-      return true;
-    }
     return false;
   // An ANDI with an 11 bit immediate will zero bits 63:11.
   case RISCV::ANDI:
@@ -304,23 +295,6 @@ static bool isSignExtendingOpW(MachineInstr &MI, MachineRegisterInfo &MRI,
   case RISCV::COPY:
     return MI.getOperand(1).getReg() == RISCV::X0;
 
-  // With these opcode, we can "fix" them with the W-version
-  // if we know all users of the result only rely on bits 31:0
-  case RISCV::SLLI:
-    // SLLIW reads the lowest 5 bits, while SLLI reads lowest 6 bits
-    if (MI.getOperand(2).getImm() >= 32)
-      return false;
-    [[fallthrough]];
-  case RISCV::ADD:
-  case RISCV::LD:
-  case RISCV::LWU:
-  case RISCV::MUL:
-  case RISCV::SUB:
-    if (hasAllWUsers(MI, MRI)) {
-      FixableDef.insert(&MI);
-      return true;
-    }
-    break;
   }
 
   return false;
@@ -342,7 +316,7 @@ static bool isSignExtendedW(MachineInstr &OrigMI, MachineRegisterInfo &MRI,
       continue;
 
     // If this is a sign extending operation we don't need to look any further.
-    if (isSignExtendingOpW(*MI, MRI, FixableDef))
+    if (isSignExtendingOpW(*MI, MRI))
       continue;
 
     // Is this an instruction that propagates sign extend?
@@ -444,6 +418,25 @@ static bool isSignExtendedW(MachineInstr &OrigMI, MachineRegisterInfo &MRI,
 
       break;
     }
+
+    // With these opcode, we can "fix" them with the W-version
+    // if we know all users of the result only rely on bits 31:0
+    case RISCV::SLLI:
+      // SLLIW reads the lowest 5 bits, while SLLI reads lowest 6 bits
+      if (MI->getOperand(2).getImm() >= 32)
+        return false;
+      [[fallthrough]];
+    case RISCV::ADDI:
+    case RISCV::ADD:
+    case RISCV::LD:
+    case RISCV::LWU:
+    case RISCV::MUL:
+    case RISCV::SUB:
+      if (hasAllWUsers(*MI, MRI)) {
+        FixableDef.insert(MI);
+        break;
+      }
+      return false;
     }
   }