microsoft/compiler: Support gl_Layer

Maps pretty nicely to SV_RenderTargetArrayIndex, so nothing complicated
here.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17039>

src/microsoft/compiler/dxil_signature.c

@@ -104,6 +104,8 @@ in_sysvalue_name(nir_variable *var)
       return "POS";
    case VARYING_SLOT_FACE:
       return "FACE";
+   case VARYING_SLOT_LAYER:
+      return "RTINDEX";
    default:
       return "NONE";
    }
@@ -326,6 +328,12 @@ get_semantic_name(nir_variable *var, struct semantic_info *info,
       info->kind = DXIL_SEM_VIEWPORT_ARRAY_INDEX;
       break;
 
+   case VARYING_SLOT_LAYER:
+      assert(glsl_get_components(var->type) == 1);
+      snprintf(info->name, 64, "%s", "SV_RenderTargetArrayIndex");
+      info->kind = DXIL_SEM_RENDERTARGET_ARRAY_INDEX;
+      break;
+
    default: {
          info->index = var->data.driver_location;
          strcpy(info->name, "TEXCOORD");

src/microsoft/compiler/nir_to_dxil.c

@@ -5440,7 +5440,8 @@ emit_module(struct ntd_context *ctx, const struct nir_to_dxil_options *opts)
       }
    } else if (ctx->shader->info.stage == MESA_SHADER_VERTEX ||
               ctx->shader->info.stage == MESA_SHADER_TESS_EVAL) {
-      if (ctx->shader->info.outputs_written & VARYING_BIT_VIEWPORT)
+      if (ctx->shader->info.outputs_written &
+          (VARYING_BIT_VIEWPORT | VARYING_BIT_LAYER))
          ctx->mod.feats.array_layer_from_vs_or_ds = true;
    }
 
@@ -5880,6 +5881,7 @@ nir_var_to_dxil_sysvalue_type(nir_variable *var, uint64_t other_stage_mask)
    case VARYING_SLOT_TESS_LEVEL_INNER:
    case VARYING_SLOT_TESS_LEVEL_OUTER:
    case VARYING_SLOT_VIEWPORT:
+   case VARYING_SLOT_LAYER:
       if (!((1ull << var->data.location) & other_stage_mask))
          return DXIL_SYSVALUE;
       FALLTHROUGH;