[llvm] [RISCV] Simplify mask operand check in VLOptimizer. NFC (PR #150373)

[Luke Lau via llvm-commits]

https://github.com/lukel97 created https://github.com/llvm/llvm-project/pull/150373

We don't need to lookup the reg class because the MCInstDesc already gives us this information.

With that we can remove some helper methods, and tighten the assert in isCandidate because all pseudos at this stage should be defining virtual registers.


>From 9614e6d4a89481378e8dd2ca267c05eb75bce989 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Thu, 24 Jul 2025 13:45:40 +0800
Subject: [PATCH] [RISCV] Simplify mask operand check in VLOptimizer. NFC

We don't need to lookup the reg class because the MCInstDesc already gives us this information.

With that we can remove some helper methods, and tighten the assert in isCandidate because all pseudos at this stage should be defining virtual registers.
---
 llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp | 35 ++++++----------------
 llvm/test/CodeGen/RISCV/rvv/vxrm.mir       |  5 ++--
 2 files changed, 12 insertions(+), 28 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
index b53d919872de5..c9464515d2e56 100644
--- a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
@@ -114,14 +114,6 @@ FunctionPass *llvm::createRISCVVLOptimizerPass() {
   return new RISCVVLOptimizer();
 }
 
-/// Return true if R is a physical or virtual vector register, false otherwise.
-static bool isVectorRegClass(Register R, const MachineRegisterInfo *MRI) {
-  if (R.isPhysical())
-    return RISCV::VRRegClass.contains(R);
-  const TargetRegisterClass *RC = MRI->getRegClass(R);
-  return RISCVRI::isVRegClass(RC->TSFlags);
-}
-
 LLVM_ATTRIBUTE_UNUSED
 static raw_ostream &operator<<(raw_ostream &OS, const OperandInfo &OI) {
   OI.print(OS);
@@ -183,37 +175,28 @@ static unsigned getIntegerExtensionOperandEEW(unsigned Factor,
   return Log2EEW;
 }
 
-/// Check whether MO is a mask operand of MI.
-static bool isMaskOperand(const MachineInstr &MI, const MachineOperand &MO,
-                          const MachineRegisterInfo *MRI) {
-
-  if (!MO.isReg() || !isVectorRegClass(MO.getReg(), MRI))
-    return false;
-
-  const MCInstrDesc &Desc = MI.getDesc();
-  return Desc.operands()[MO.getOperandNo()].RegClass == RISCV::VMV0RegClassID;
-}
-
 static std::optional<unsigned>
 getOperandLog2EEW(const MachineOperand &MO, const MachineRegisterInfo *MRI) {
   const MachineInstr &MI = *MO.getParent();
+  const MCInstrDesc &Desc = MI.getDesc();
   const RISCVVPseudosTable::PseudoInfo *RVV =
       RISCVVPseudosTable::getPseudoInfo(MI.getOpcode());
   assert(RVV && "Could not find MI in PseudoTable");
 
   // MI has a SEW associated with it. The RVV specification defines
   // the EEW of each operand and definition in relation to MI.SEW.
-  unsigned MILog2SEW =
-      MI.getOperand(RISCVII::getSEWOpNum(MI.getDesc())).getImm();
+  unsigned MILog2SEW = MI.getOperand(RISCVII::getSEWOpNum(Desc)).getImm();
 
-  const bool HasPassthru = RISCVII::isFirstDefTiedToFirstUse(MI.getDesc());
-  const bool IsTied = RISCVII::isTiedPseudo(MI.getDesc().TSFlags);
+  const bool HasPassthru = RISCVII::isFirstDefTiedToFirstUse(Desc);
+  const bool IsTied = RISCVII::isTiedPseudo(Desc.TSFlags);
 
   bool IsMODef = MO.getOperandNo() == 0 ||
                  (HasPassthru && MO.getOperandNo() == MI.getNumExplicitDefs());
 
   // All mask operands have EEW=1
-  if (isMaskOperand(MI, MO, MRI))
+  const MCOperandInfo &Info = Desc.operands()[MO.getOperandNo()];
+  if (Info.OperandType == MCOI::OPERAND_REGISTER &&
+      Info.RegClass == RISCV::VMV0RegClassID)
     return 0;
 
   // switch against BaseInstr to reduce number of cases that need to be
@@ -1296,8 +1279,8 @@ bool RISCVVLOptimizer::isCandidate(const MachineInstr &MI) const {
              TII->get(RISCV::getRVVMCOpcode(MI.getOpcode())).TSFlags) &&
          "Instruction shouldn't be supported if elements depend on VL");
 
-  assert(MI.getOperand(0).isReg() &&
-         isVectorRegClass(MI.getOperand(0).getReg(), MRI) &&
+  assert(RISCVRI::isVRegClass(
+             MRI->getRegClass(MI.getOperand(0).getReg())->TSFlags) &&
          "All supported instructions produce a vector register result");
 
   LLVM_DEBUG(dbgs() << "Found a candidate for VL reduction: " << MI << "\n");
diff --git a/llvm/test/CodeGen/RISCV/rvv/vxrm.mir b/llvm/test/CodeGen/RISCV/rvv/vxrm.mir
index 2bac1eeb90609..87787c1f25f09 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vxrm.mir
+++ b/llvm/test/CodeGen/RISCV/rvv/vxrm.mir
@@ -13,7 +13,7 @@ body:     |
     ; MIR-NEXT: {{  $}}
     ; MIR-NEXT: WriteVXRMImm 0, implicit-def $vxrm
     ; MIR-NEXT: dead $x0 = PseudoVSETVLI killed renamable $x10, 197 /* e8, mf8, ta, ma */, implicit-def $vl, implicit-def $vtype
-    ; MIR-NEXT: renamable $v8 = PseudoVAADD_VV_MF8 undef $v8, killed renamable $v8, killed renamable $v9, 0, $noreg, 3 /* e8 */, 0  /* tu, mu */, implicit $vxrm, implicit $vl, implicit $vtype
+    ; MIR-NEXT: renamable $v8 = PseudoVAADD_VV_MF8 undef renamable $v8, killed renamable $v8, killed renamable $v9, 0, $noreg, 3 /* e8 */, 0  /* tu, mu */, implicit $vxrm, implicit $vl, implicit $vtype
     ; MIR-NEXT: PseudoRET implicit $v8
     ; ASM-LABEL: verify_vxrm:
     ; ASM:        # %bb.0:
@@ -24,6 +24,7 @@ body:     |
     %0:vr = COPY $v8
     %1:vr = COPY $v9
     %2:gprnox0 = COPY $x10
-    renamable $v8 = PseudoVAADD_VV_MF8 undef $noreg, %0, %1, 0, %2, 3 /* e8 */, 0
+    %3:vr = PseudoVAADD_VV_MF8 undef $noreg, %0, %1, 0, %2, 3 /* e8 */, 0
+    $v8 = COPY %3
     PseudoRET implicit $v8
 ...