nir: lower is/load_helper to zero if no helper lanes are needed

If there are no helper invocations required during the
execution of the shader, we can assume that there also
are no helper invocations active.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9058>

diff --git a/src/compiler/nir/nir_lower_discard_or_demote.c b/src/compiler/nir/nir_lower_discard_or_demote.c
index f039d2879fa667f3220b69e83667a61d251c0890..037022503e824f6564c5ff06333fc78a3ee73c31 100644 (file)
--- a/src/compiler/nir/nir_lower_discard_or_demote.c
+++ b/src/compiler/nir/nir_lower_discard_or_demote.c
@@ -62,8 +62,15 @@ nir_lower_demote_to_discard_instr(nir_builder *b, nir_instr *instr, void *data)
       intrin->intrinsic = nir_intrinsic_discard_if;
       return true;
    case nir_intrinsic_is_helper_invocation:
-      intrin->intrinsic = nir_intrinsic_load_helper_invocation;
+   case nir_intrinsic_load_helper_invocation: {
+      /* If the shader doesn't need helper invocations,
+       * we can assume there are none */
+      b->cursor = nir_before_instr(instr);
+      nir_ssa_def *zero = nir_imm_false(b);
+      nir_ssa_def_rewrite_uses_ssa(&intrin->dest.ssa, zero);
+      nir_instr_remove_v(instr);
       return true;
+   }
    default:
       return false;
    }