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

[fhahn]

Summary

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

[anemet]

LGTM!

llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp

for (BasicBlock &BB : Func)
         case Intrinsic::matrix_column_major_store:
           WorkList.push_back(&Inst);
           break;
         default:
           break;
         }
       }
 
+    // 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);
       WorkList = propagateShapeBackward(WorkList);
     }
 
     bool Changed = false;
     SmallVector<CallInst *, 16> MaybeFusableInsts;