Potential correctness issue with stmatrix

[naoyam]

In tests using stmatrix, e.g, MmaTest/HopperRSStmatrix.SingleTileWithTMALoadStoreStMatrix/4, generated code has a pattern like:

   #pragma unroll
   for(nvfuser_index_t i39 = 0; i39 < 3; ++i39) {
     arraySet<__half, 4>(&T5[(i8 + (8 * i39))], (__half)0);
   }
   #pragma unroll
   for(nvfuser_index_t i39 = 0; i39 < 3; ++i39) {
     if ((b13 && (i14 < (-(8 * i39))))) {
       stmatrix2(...);

Here, T5 is initialized to 0 for predicate elimination and then set by the following stmatrix op. To make this work correctly, a syncthreads should be placed between the arraySet and stmatrix2; otherwise, there could be a WAW race.

A true fix, however, would be likely removing the zero initialization. It should not be necessary as the whole buffer is entirely written into.