[llvm] [LV] Widen truncated induction updates, not just truncated phis (PR #220730)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -955,12 +998,13 @@ class LoopVectorizationCostModel {
     // update instruction to each iteration of the loop. We exclude from this
     // check the primary induction variable since it will need an update
     // instruction regardless.
-    Value *Op = Trunc->getOperand(0);
-    if (Op != Legal->getPrimaryInduction() && TTI.isTruncateFree(SrcTy, DestTy))
+    if (Info.Phi != Legal->getPrimaryInduction() &&
+        TTI.isTruncateFree(SrcTy, DestTy))
       return false;
 
-    // If the truncated value is not an induction variable, return false.
-    return Legal->isInductionPhi(Op);
+    if (IVInfo)
+      *IVInfo = Info;
+    return true;
----------------
artagnon wrote:

Why not just return a `std::optional<OptimizableIVTruncateInfo>` and strip the pointer arg?

https://github.com/llvm/llvm-project/pull/220730