nak: Lower away ldcx when NAK_DEBUG=no_ugpr is set

Reviewed-by: Mel Henning <mhenning@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36995>

src/nouveau/compiler/nak/api.rs

@@ -107,6 +107,11 @@ pub extern "C" fn nak_should_print_nir() -> bool {
     DEBUG.print()
 }
 
+#[no_mangle]
+pub extern "C" fn nak_debug_no_ugpr() -> bool {
+    DEBUG.no_ugpr()
+}
+
 fn nir_options(dev: &nv_device_info) -> nir_shader_compiler_options {
     let mut op: nir_shader_compiler_options = Default::default();
 

src/nouveau/compiler/nak_nir_lower_non_uniform_ldcx.c

@@ -72,6 +72,17 @@ lower_ldcx_to_global(nir_builder *b, nir_intrinsic_instr *load,
    nir_def_replace(&load->def, val);
 }
 
+static bool
+lower_all_ldcx_to_global_intrin(nir_builder *b, nir_intrinsic_instr *load,
+                                void *data)
+{
+   if (load->intrinsic != nir_intrinsic_ldcx_nv)
+      return false;
+
+   lower_ldcx_to_global(b, load, data);
+   return true;
+}
+
 struct non_uniform_section {
    nir_block *pred;
    nir_block *succ;
@@ -491,6 +502,12 @@ bool
 nak_nir_lower_non_uniform_ldcx(nir_shader *nir,
                                const struct nak_compiler *nak)
 {
+   /* If we don't have UGPRs, lower all of them. */
+   if (nak_debug_no_ugpr()) {
+      return nir_shader_intrinsics_pass(nir, lower_all_ldcx_to_global_intrin,
+                                        nir_metadata_none, (void *)nak);
+   }
+
    /* Real functions are going to make hash of this */
    nir_function_impl *impl = nir_shader_get_entrypoint(nir);
    nir_builder b = nir_builder_create(impl);

src/nouveau/compiler/nak_private.h

@@ -15,6 +15,7 @@ extern "C" {
 #endif
 
 bool nak_should_print_nir(void);
+bool nak_debug_no_ugpr(void);
 
 struct nak_compiler {
    uint8_t sm;