intel/blorp: Lower base_workgroup_id to zero

We don't use a base workgroup ID for BLOCS.  It needs to be lowered, or
else we'll assert fail when compiling the compute shader.

(Note for stable: this patch doesn't fix a bug in 4abdecce22
specifically, but rather is a missing patch that needed to go along with
the rest of MR 20068, on whichever branches it exists on.)

Fixes: 4abdecce22 ("iris: Lower load_base_workgroup_id to zero")
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20750>

src/intel/blorp/blorp.c

@@ -348,6 +348,22 @@ blorp_compile_vs(struct blorp_context *blorp, void *mem_ctx,
    return brw_compile_vs(compiler, mem_ctx, &params);
 }
 
+static bool
+lower_base_workgroup_id(nir_builder *b, nir_instr *instr, UNUSED void *data)
+{
+   if (instr->type != nir_instr_type_intrinsic)
+      return false;
+
+   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+
+   if (intrin->intrinsic != nir_intrinsic_load_base_workgroup_id)
+      return false;
+
+   b->cursor = nir_instr_remove(&intrin->instr);
+   nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_imm_zero(b, 3, 32));
+   return true;
+}
+
 const unsigned *
 blorp_compile_cs(struct blorp_context *blorp, void *mem_ctx,
                  struct nir_shader *nir,
@@ -375,6 +391,8 @@ blorp_compile_cs(struct blorp_context *blorp, void *mem_ctx,
    cs_prog_data->base.param = rzalloc_array(NULL, uint32_t, nr_params);
 
    NIR_PASS_V(nir, brw_nir_lower_cs_intrinsics);
+   NIR_PASS_V(nir, nir_shader_instructions_pass, lower_base_workgroup_id,
+              nir_metadata_block_index | nir_metadata_dominance, NULL);
 
    struct brw_compile_cs_params params = {
       .nir = nir,