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

[via llvm-commits]

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@@ -934,8 +934,19 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
 
   IRBuilder<> Builder(State.CFG.PrevBB->getTerminator());
   // FIXME: Model VF * UF computation completely in VPlan.
-  VFxUF.setUnderlyingValue(
-      createStepForVF(Builder, TripCountV->getType(), State.VF, State.UF));
+  if (VF.getNumUsers()) {
+    Value *RuntimeVF =
+        createStepForVF(Builder, TripCountV->getType(), State.VF, 1);
+    VF.setUnderlyingValue(RuntimeVF);
+    VFxUF.setUnderlyingValue(
+        State.UF > 1
+            ? Builder.CreateMul(
+                  RuntimeVF, ConstantInt::get(TripCountV->getType(), State.UF))
+            : RuntimeVF);
+  } else {
+    VFxUF.setUnderlyingValue(
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ayalz wrote:

> Yes, VFxUF is used to increment the canonical induction, which is present in almost all cases, but could also be done only if users exist.

Exceptional use-less cases are loops whose trip count is VFxUF - where optimizeForVFAndUF() discards the canonical IV's increment by VFxUF?


So one way to improve consistency, w/o changing too many tests, would be to (also) set VFxUF only if used? Although logically it should always be used - to set the vector trip count(?).

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