[Matrix] Bail out early if there are no matrix intrinsics.

If there are no matrix intrinsics in a function, we can directly bail
out, as there's nothing left to do.

Reviewed By: anemet

Differential Revision: https://reviews.llvm.org/D102931

llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp

@@ -677,6 +677,10 @@ class LowerMatrixIntrinsics {
         }
       }
 
+    // Avoid unnecessary work if there are no matrix intrinsics in the function.
+    if (WorkList.empty())
+      return false;
+
     // Propagate shapes until nothing changes any longer.
     while (!WorkList.empty()) {
       WorkList = propagateShapeForward(WorkList);