pan/bi: Add some zero bytes after shaders on Bifrost

Bifrost will prefetch bytes after the end of shaders, so make sure
these bytes are allocated and zeroed.

Fixes GPU faults in Xonotic.

Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8428>

src/panfrost/bifrost/bifrost_compile.c

@@ -2236,6 +2236,10 @@ bifrost_compile_shader_nir(void *mem_ctx, nir_shader *nir,
                                 bifrost_debug & BIFROST_DBG_VERBOSE);
         }
 
+        /* Pad the shader with enough zero bytes to trick the prefetcher */
+        memset(util_dynarray_grow(&program->compiled, uint8_t, BIFROST_SHADER_PREFETCH),
+               0, BIFROST_SHADER_PREFETCH);
+
         program->tls_size = ctx->tls_size;
 
         if ((bifrost_debug & BIFROST_DBG_SHADERDB || inputs->shaderdb) &&