zink: wrap discard in a function

This makes discard less weird, and allows us to treat it as
control-flow. This makes things less bizarre for drivers.

Cc: mesa-stable
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7070
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18244>

diff --git a/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c b/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c
index 2a3bd81..93ec737 100644 (file)
--- a/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c
+++ b/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c
@@ -107,6 +107,8 @@ struct ntv_context {
          subgroup_le_mask_var,
          subgroup_lt_mask_var,
          subgroup_size_var;
+
+   SpvId discard_func;
 };
 
 static SpvId
@@ -2345,11 +2347,10 @@ emit_load_const(struct ntv_context *ctx, nir_load_const_instr *load_const)
 static void
 emit_discard(struct ntv_context *ctx, nir_intrinsic_instr *intr)
 {
-   assert(ctx->block_started);
-   spirv_builder_emit_kill(&ctx->builder);
-   /* discard is weird in NIR, so let's just create an unreachable block after
-      it and hope that the vulkan driver will DCE any instructinos in it. */
-   spirv_builder_label(&ctx->builder, spirv_builder_new_id(&ctx->builder));
+   assert(ctx->discard_func);
+   SpvId type_void = spirv_builder_type_void(&ctx->builder);
+   spirv_builder_function_call(&ctx->builder, type_void,
+                               ctx->discard_func, NULL, 0);
 }
 
 static void
@@ -4411,6 +4412,19 @@ nir_to_spirv(struct nir_shader *s, const struct zink_shader_info *sinfo, uint32_
       spirv_builder_emit_exec_mode(&ctx.builder, entry_point,
                                    SpvExecutionModeXfb);
    }
+
+   if (s->info.stage == MESA_SHADER_FRAGMENT && s->info.fs.uses_discard) {
+      ctx.discard_func = spirv_builder_new_id(&ctx.builder);
+      spirv_builder_emit_name(&ctx.builder, ctx.discard_func, "discard");
+      spirv_builder_function(&ctx.builder, ctx.discard_func, type_void,
+                             SpvFunctionControlMaskNone,
+                             type_void_func);
+      SpvId label = spirv_builder_new_id(&ctx.builder);
+      spirv_builder_label(&ctx.builder, label);
+      spirv_builder_emit_kill(&ctx.builder);
+      spirv_builder_function_end(&ctx.builder);
+   }
+
    spirv_builder_function(&ctx.builder, entry_point, type_void,
                           SpvFunctionControlMaskNone,
                           type_void_func);