[llvm] [VPlan] Add VPInst::getNumOperandsForOpcode, use to verify in ctor (NFC) (PR #142284)

[via llvm-commits]

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@@ -415,8 +415,65 @@ VPInstruction::VPInstruction(unsigned Opcode, ArrayRef<VPValue *> Operands,
       VPIRMetadata(), Opcode(Opcode), Name(Name.str()) {
   assert(flagsValidForOpcode(getOpcode()) &&
          "Set flags not supported for the provided opcode");
+  assert((getNumOperandsForOpcode(Opcode) == -1u ||
+          getNumOperandsForOpcode(Opcode) == getNumOperands()) &&
+         "number of operands does not match opcode");
 }
 
+#ifndef NDEBUG
+unsigned VPInstruction::getNumOperandsForOpcode(unsigned Opcode) {
+  if (Instruction::isUnaryOp(Opcode) || Instruction::isCast(Opcode))
+    return 1;
+
+  if (Instruction::isBinaryOp(Opcode))
+    return 2;
+
+  switch (Opcode) {
+  case VPInstruction::StepVector:
+    return 0;
+  case Instruction::Alloca:
+  case Instruction::ExtractValue:
+  case Instruction::Freeze:
+  case Instruction::Load:
+  case VPInstruction::AnyOf:
+  case VPInstruction::BranchOnCond:
+  case VPInstruction::CalculateTripCountMinusVF:
+  case VPInstruction::CanonicalIVIncrementForPart:
+  case VPInstruction::ExplicitVectorLength:
+  case VPInstruction::ExtractLastElement:
+  case VPInstruction::ExtractPenultimateElement:
+  case VPInstruction::FirstActiveLane:
+  case VPInstruction::Not:
+    return 1;
+
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ayalz wrote:

```suggestion
```
consistency

https://github.com/llvm/llvm-project/pull/142284