[LV] Use more precise isPredicatedInst in legacy CCH (NFC).

Legal::isMaskRequired may be overly conservative and also return true
when no mask is actually required.

Use isPredicatedInst from the cost model instead, which fixes a
cost-model divergence between legacy and VPlan cost model where the
legacy cost model incorrectly assumed some loads were predicated.

Fixes #148431.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -6289,8 +6289,8 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I,
         return TTI::CastContextHint::Interleave;
       case LoopVectorizationCostModel::CM_Scalarize:
       case LoopVectorizationCostModel::CM_Widen:
-        return Legal->isMaskRequired(I) ? TTI::CastContextHint::Masked
-                                        : TTI::CastContextHint::Normal;
+        return isPredicatedInst(I) ? TTI::CastContextHint::Masked
+                                   : TTI::CastContextHint::Normal;
       case LoopVectorizationCostModel::CM_Widen_Reverse:
         return TTI::CastContextHint::Reversed;
       case LoopVectorizationCostModel::CM_Unknown: