brw: bound the amount of rematerialized NIR instructions

Some of the instructions we don't need to rematerialize because we
already know they are executed with NoMask so we can use their
destination without reemitting them again.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29663>

src/intel/compiler/brw_fs_nir.cpp

@@ -4539,6 +4539,28 @@ struct rebuild_resource {
    std::vector<nir_def *> array;
 };
 
+static bool
+skip_rebuild_instr(nir_instr *instr)
+{
+   if (instr->type != nir_instr_type_intrinsic)
+      return false;
+
+   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+   switch (intrin->intrinsic) {
+   case nir_intrinsic_load_ubo_uniform_block_intel:
+   case nir_intrinsic_load_ssbo_uniform_block_intel:
+   case nir_intrinsic_load_global_constant_uniform_block_intel:
+      /* Those intrinsic are generated using NoMask so we can trust their
+       * destination registers are fully populated. No need to rematerialize
+       * further.
+       */
+      return true;
+
+   default:
+      return false;
+   }
+}
+
 static bool
 add_rebuild_src(nir_src *src, void *state)
 {
@@ -4549,7 +4571,8 @@ add_rebuild_src(nir_src *src, void *state)
          return true;
    }
 
-   nir_foreach_src(src->ssa->parent_instr, add_rebuild_src, state);
+   if (!skip_rebuild_instr(src->ssa->parent_instr))
+      nir_foreach_src(src->ssa->parent_instr, add_rebuild_src, state);
    res->array.push_back(src->ssa);
    return true;
 }