[DAG] Use correct size for truncated store merge of load. NFCI.

Avoid non-legal memory ops by checking correct size when merging
stores of loads into a extload-truncstore pair.

llvm-svn: 305466

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -12959,8 +12959,8 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode *St) {
             TLI.allowsMemoryAccess(Context, DL, LegalizedStoredValueTy,
                                    FirstStoreAS, FirstStoreAlign, &IsFastSt) &&
             IsFastSt &&
-            TLI.allowsMemoryAccess(Context, DL, LegalizedStoredValueTy,
-                                   FirstLoadAS, FirstLoadAlign, &IsFastLd) &&
+            TLI.allowsMemoryAccess(Context, DL, StoreTy, FirstLoadAS,
+                                   FirstLoadAlign, &IsFastLd) &&
             IsFastLd)
           LastLegalIntegerType = i + 1;
       }