[llvm] [VPlan] Encode single-scalar-ness of VPInstruction in a field (NFC). (PR #227761)

[Ramkumar Ramachandra via llvm-commits]

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@@ -605,15 +605,36 @@ Type *VPReplicateRecipe::computeScalarType(const Instruction *I,
   return computeScalarTypeForInstruction(Opcode, Operands);
 }
 
+/// Returns true if VPInstructions with \p Opcode always produce a single
+/// scalar.
+static bool isAlwaysSingleScalar(unsigned Opcode) {
+  switch (Opcode) {
+  case Instruction::Load:
+  case Instruction::PHI:
+  case VPInstruction::ExplicitVectorLength:
+  case VPInstruction::ResumeForEpilogue:
+  case VPInstruction::Intrinsic:
+    return true;
+  default:
+    return false;
+  }
+}
+
 VPInstruction::VPInstruction(unsigned Opcode, ArrayRef<VPValue *> Operands,
                              const VPIRFlags &Flags, const VPIRMetadata &MD,
-                             DebugLoc DL, const Twine &Name, Type *ResultTy)
+                             DebugLoc DL, const Twine &Name, Type *ResultTy,
+                             std::optional<bool> GeneratesSingleScalar)
     : VPRecipeWithIRFlags(
           VPRecipeBase::VPInstructionSC, Operands,
           ResultTy ? ResultTy
                    : computeScalarTypeForInstruction(Opcode, Operands),
           Flags, DL),
-      VPIRMetadata(MD), Opcode(Opcode), Name(Name.str()) {
+      VPIRMetadata(MD), Opcode(Opcode), Name(Name.str()),
+      GeneratesSingleScalar(
+          GeneratesSingleScalar.value_or(isAlwaysSingleScalar(Opcode))) {
+  assert((!isAlwaysSingleScalar(Opcode) || this->GeneratesSingleScalar) &&
+         "GeneratesSingleScalar must be set for opcodes that always generate "
+         "a single scalar");
----------------
artagnon wrote:

Hm, I'm confused by this assert: if GeneratesSingleScalar is supplied, use it; otherwise use isAlwaysSingleScalar. If it is not isAlwaysSingleScalar, a GeneratesSingleScalar must be supplied. Accordingly, the message should be "GeneratesSingleSingleScalar must be supplied for opcodes that are not determined always-single-scalar"?

https://github.com/llvm/llvm-project/pull/227761