Refactor getSameRatioLMUL so we can reuse it, add setVLMul accessor

Author: lukel97

llvm/lib/Target/RISCV/MCA/RISCVCustomBehaviour.cpp

@@ -212,9 +212,10 @@ getEEWAndEMULForUnitStrideLoadStore(unsigned Opcode, RISCVII::VLMUL LMUL,
     llvm_unreachable("Opcode is not a vector unit stride load nor store");
   }
 
-  uint8_t EMUL =
-      static_cast<uint8_t>(RISCVVType::getSameRatioLMUL(SEW, LMUL, EEW));
-  return std::make_pair(EEW, EMUL);
+  auto EMUL = RISCVVType::getSameRatioLMUL(SEW, LMUL, EEW);
+  if (!EEW)
+    llvm_unreachable("Invalid SEW or LMUL for new ratio");
+  return std::make_pair(EEW, *EMUL);
 }
 
 unsigned RISCVInstrumentManager::getSchedClassID(

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.cpp

@@ -206,12 +206,14 @@ unsigned RISCVVType::getSEWLMULRatio(unsigned SEW, RISCVII::VLMUL VLMul) {
   return (SEW * 8) / LMul;
 }
 
-RISCVII::VLMUL RISCVVType::getSameRatioLMUL(unsigned SEW, RISCVII::VLMUL VLMUL,
-                                            unsigned EEW) {
+std::optional<RISCVII::VLMUL>
+RISCVVType::getSameRatioLMUL(unsigned SEW, RISCVII::VLMUL VLMUL, unsigned EEW) {
   unsigned Ratio = RISCVVType::getSEWLMULRatio(SEW, VLMUL);
   unsigned EMULFixedPoint = (EEW * 8) / Ratio;
   bool Fractional = EMULFixedPoint < 8;
   unsigned EMUL = Fractional ? 8 / EMULFixedPoint : EMULFixedPoint / 8;
+  if (!isValidLMUL(EMUL, Fractional))
+    return std::nullopt;
   return RISCVVType::encodeLMUL(EMUL, Fractional);
 }
 

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -535,8 +535,8 @@ void printVType(unsigned VType, raw_ostream &OS);
 
 unsigned getSEWLMULRatio(unsigned SEW, RISCVII::VLMUL VLMul);
 
-RISCVII::VLMUL getSameRatioLMUL(unsigned SEW, RISCVII::VLMUL VLMUL,
-                                unsigned EEW);
+std::optional<RISCVII::VLMUL>
+getSameRatioLMUL(unsigned SEW, RISCVII::VLMUL VLMUL, unsigned EEW);
 } // namespace RISCVVType
 
 namespace RISCVRVC {

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -539,6 +539,8 @@ class VSETVLIInfo {
     MaskAgnostic = MA;
   }
 
+  void setVLMul(RISCVII::VLMUL VLMul) { this->VLMul = VLMul; }
+
   unsigned encodeVTYPE() const {
     assert(isValid() && !isUnknown() && !SEWLMULRatioOnly &&
            "Can't encode VTYPE for uninitialized or unknown");
@@ -1041,21 +1043,13 @@ void RISCVInsertVSETVLI::transferBefore(VSETVLIInfo &Info,
   // If we don't use LMUL or the SEW/LMUL ratio, then adjust LMUL so that we
   // maintain the SEW/LMUL ratio. This allows us to eliminate VL toggles in more
   // places.
-  DemandedFields Demanded = getDemanded(MI, MRI);
+  DemandedFields Demanded = getDemanded(MI, MRI, ST);
   if (!Demanded.LMUL && !Demanded.SEWLMULRatio && Info.isValid() &&
       PrevInfo.isValid() && !Info.isUnknown() && !PrevInfo.isUnknown() &&
       !Info.hasSameVLMAX(PrevInfo)) {
-    unsigned SEW = Info.getSEW();
-    // Fixed point value with 3 fractional bits.
-    unsigned NewRatio = (SEW * 8) / PrevInfo.getSEWLMULRatio();
-    if (NewRatio >= 1 && NewRatio <= 64) {
-      bool Fractional = NewRatio < 8;
-      RISCVII::VLMUL NewVLMul = RISCVVType::encodeLMUL(
-          Fractional ? 8 / NewRatio : NewRatio / 8, Fractional);
-      unsigned VType = Info.encodeVTYPE();
-      Info.setVTYPE(NewVLMul, SEW, RISCVVType::isTailAgnostic(VType),
-                    RISCVVType::isMaskAgnostic(VType));
-    }
+    if (auto NewVLMul = RISCVVType::getSameRatioLMUL(
+            PrevInfo.getSEW(), PrevInfo.getVLMUL(), Info.getSEW()))
+      Info.setVLMul(*NewVLMul);
   }
 
   // For vmv.s.x and vfmv.s.f, there are only two behaviors, VL = 0 and