[llvm] [LV]Set tailfolding styles before computing feasible max VF. (PR #91403)

[Alexey Bataev via llvm-commits]

================
@@ -4229,9 +4248,20 @@ LoopVectorizationCostModel::getMaxLegalScalableVF(unsigned MaxSafeElements) {
     reportVectorizationInfo("Scalable vectorization is not supported "
                             "for all element types found in this loop.",
                             "ScalableVFUnfeasible", ORE, TheLoop);
-    return ElementCount::getScalable(0);
+    return false;
   }
 
+  IsScalableVectorizationAllowed = true;
+  return true;
+}
+
+ElementCount
+LoopVectorizationCostModel::getMaxLegalScalableVF(unsigned MaxSafeElements) {
+  if (!isScalableVectorizationAllowed())
+    return ElementCount::getScalable(0);
+
+  auto MaxScalableVF = ElementCount::getScalable(
+      std::numeric_limits<ElementCount::ScalarTy>::max());
----------------
alexey-bataev wrote:

1. Do not know how to add the assertion here without looking into internals of the LoopAccessAnalysis. Legal->isSafeForAnyVectorWidth() checks that MaxSafeVectorWidthInBits == UINT_MAX, and MaxSafeElements = bit_floor(MaxSafeVectorWidthInBits / WidestType).

2. Not only. If MaxSafeElements < MaxVScale too.

https://github.com/llvm/llvm-project/pull/91403