nir/peephole_select: add option to allow discard without ~0 limit

Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33590>

src/compiler/nir/nir.h

@@ -6062,6 +6062,7 @@ typedef struct nir_opt_peephole_select_options {
    unsigned limit; /* Set to max to flatten all control flow. */
    bool indirect_load_ok;
    bool expensive_alu_ok;
+   bool discard_ok;
 } nir_opt_peephole_select_options;
 
 bool nir_opt_peephole_select(nir_shader *shader,

src/compiler/nir/nir_opt_peephole_select.c

@@ -195,6 +195,14 @@ block_check_for_allowed_instrs(nir_block *block, unsigned *count,
                return false;
             break;
 
+         case nir_intrinsic_terminate:
+         case nir_intrinsic_terminate_if:
+         case nir_intrinsic_demote:
+         case nir_intrinsic_demote_if:
+            if (!options->discard_ok)
+               return false;
+            break;
+
          default:
             return false;
          }
@@ -296,9 +304,7 @@ get_options_for_if(nir_if *if_stmt,
    return if_options;
 }
 
-/* If we're moving discards out of the if for non-CF hardware, we need to add
- * the if's condition to it
- */
+/* If we're moving discards out of the if we need to add the if's condition to it */
 static void
 rewrite_discard_conds(nir_instr *instr, nir_def *if_cond, bool is_else)
 {

src/gallium/frontends/rusticl/core/kernel.rs

@@ -592,6 +592,7 @@ fn opt_nir(nir: &mut NirShader, dev: &Device, has_explicit_types: bool) {
             limit: 8,
             indirect_load_ok: true,
             expensive_alu_ok: true,
+            discard_ok: false,
         };
         progress |= nir_pass!(nir, nir_opt_peephole_select, &peephole_select_options);
         progress |= nir_pass!(