[Transforms] Avoid repeated hash lookups (NFC) (#113120)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp

@@ -1462,9 +1462,12 @@ class LowerMatrixIntrinsics {
       if (!CanBeFlattened(Op))
         return;
 
-      if (match(Op, m_BinOp()) && ShapeMap.find(Op) != ShapeMap.end()) {
-        ShapeMap[Op] = ShapeMap[Op].t();
-        return;
+      if (match(Op, m_BinOp())) {
+        auto It = ShapeMap.find(Op);
+        if (It != ShapeMap.end()) {
+          It->second = It->second.t();
+          return;
+        }
       }
 
       FusedInsts.insert(cast<Instruction>(Op));