[llvm] [VPlan] Add VPValue for VF, use it for VPWidenIntOrFpInductionRecipe. (PR #95305)

[via llvm-commits]

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@@ -8189,10 +8189,12 @@ createWidenInductionRecipes(PHINode *Phi, Instruction *PhiOrTrunc,
   VPValue *Step =
       vputils::getOrCreateVPValueForSCEVExpr(Plan, IndDesc.getStep(), SE);
   if (auto *TruncI = dyn_cast<TruncInst>(PhiOrTrunc)) {
-    return new VPWidenIntOrFpInductionRecipe(Phi, Start, Step, IndDesc, TruncI);
+    return new VPWidenIntOrFpInductionRecipe(Phi, Start, Step, Plan.getVF(),
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ayalz wrote:

>> VPWidenIntOrFpInductionRecipe could retrieve VF by looking up Plan.getVF() on demand rather than recording it as on operand, but the latter helps in checking if VF has users, i.e., if any VPWidenIntOrFpInductionRecipe exists?

> Exactly, this is used to check whether to generate it or not. VFxUF is similarly added as operand to the VPInstruction to increment the canonical IV.

Agree to model usage and dependence of values directly via explicit operands, rather than by retrieving them from plan (or region).

If/when VFxUF becomes a Mul VPInstruction which uses VF (and UF), will the check for no VF users change to check if VF is used only by this Mul?

Could this folding be done by a subsequent VPlan2VPlan pass? Would indeed be good to reduce amount of test changes...

https://github.com/llvm/llvm-project/pull/95305