[llvm] [LV] Use IVUpdateMayOverflow to set HasNUW. (PR #111758)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -9014,9 +9014,11 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
 
   DebugLoc DL = getDebugLocFromInstOrOperands(Legal->getPrimaryInduction());
   TailFoldingStyle Style = CM.getTailFoldingStyle(IVUpdateMayOverflow);
-  // When not folding the tail, we know that the induction increment will not
-  // overflow.
-  bool HasNUW = Style == TailFoldingStyle::None;
+  // Use NUW for the induction increment if we proved that it won't overflow in
+  // the vector loop or when not folding the tail. Then we know that the
+  // induction increment will not overflow as the vector trip count is >=
+  // increment and a multiple of the increment.
----------------
artagnon wrote:

Is this correct: "the vector trip count >= increment and a multiple of the increment"? The trip count of the vectorized loop could be 1 for a VF of 4: won't the increment also be multiplied by 4 from the scalar version then? If the IV update doesn't overflow, doesn't it mean that trip count of vectorized loop * VF >= increment and a multiple of the increment? Maybe I'm getting confused with the "vector trip count" terminology.

https://github.com/llvm/llvm-project/pull/111758