[llvm] [VPlan] Implement interleaving as VPlan-to-VPlan transform. (PR #95842)

[via llvm-commits]

================
@@ -332,6 +332,12 @@ FastMathFlags VPRecipeWithIRFlags::getFastMathFlags() const {
   return Res;
 }
 
+unsigned VPInstruction::getUnrollPartOperand() const {
+  assert(getOpcode() == VPInstruction::CanonicalIVIncrementForPart &&
+         getNumOperands() == 2 && "Called for unsupported recipe");
+  return cast<ConstantInt>(getOperand(1)->getLiveInIRValue())->getZExtValue();
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ayalz wrote:

Suggestion is to have
```
  VPValue *UnrollPartOperand = getUnrollPartOperand();
```
  which returns null if VPInstruction has no such operand (not a CanonicalIVIncrementForPart VPInstruction or number of operand not 2), otherwise returns the 2nd operand, and then have
```suggestion
  assert(UnrollPartOperand && "UnrollPartOperand is absent");
  return cast<ConstantInt>(UnrollPartOperand->getLiveInIRValue())->getZExtValue();
```

https://github.com/llvm/llvm-project/pull/95842