radeonsi: handle ignored LAYER and VIEWPORT_INDEX writes

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>

diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index 0bda187cfd2c2207128fa8379093f4841e778c08..00264b57963020059d5de896b189ba58201ba952 100644 (file)
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -2686,6 +2686,26 @@ static void si_llvm_emit_ls_epilogue(struct lp_build_tgsi_context *bld_base)
                LLVMValueRef *out_ptr = ctx->outputs[i];
                unsigned name = info->output_semantic_name[i];
                unsigned index = info->output_semantic_index[i];
+
+               /* The ARB_shader_viewport_layer_array spec contains the
+                * following issue:
+                *
+                *    2) What happens if gl_ViewportIndex or gl_Layer is
+                *    written in the vertex shader and a geometry shader is
+                *    present?
+                *
+                *    RESOLVED: The value written by the last vertex processing
+                *    stage is used. If the last vertex processing stage
+                *    (vertex, tessellation evaluation or geometry) does not
+                *    statically assign to gl_ViewportIndex or gl_Layer, index
+                *    or layer zero is assumed.
+                *
+                * So writes to those outputs in VS-as-LS are simply ignored.
+                */
+               if (name == TGSI_SEMANTIC_LAYER ||
+                   name == TGSI_SEMANTIC_VIEWPORT_INDEX)
+                       continue;
+
                int param = si_shader_io_get_unique_index(name, index);
                LLVMValueRef dw_addr = LLVMBuildAdd(gallivm->builder, base_dw_addr,
                                        LLVMConstInt(ctx->i32, param * 4, 0), "");