Mesa (main): ac/nir: skip gl_ViewportIndex and gl_Layer write in ES

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Module: Mesa
Branch: main
Commit: 7ddd15f6c70632c92cb15f884c943068035635a3
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=7ddd15f6c70632c92cb15f884c943068035635a3

Author: Qiang Yu <yuq825 at gmail.com>
Date:   Mon May 30 14:52:57 2022 +0800

ac/nir: skip gl_ViewportIndex and gl_Layer write in ES

Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Reviewed-by: Timur Kristóf <timur.kristof at gmail.com>
Signed-off-by: Qiang Yu <yuq825 at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16788>

---

 src/amd/common/ac_nir_lower_esgs_io_to_mem.c | 32 ++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/src/amd/common/ac_nir_lower_esgs_io_to_mem.c b/src/amd/common/ac_nir_lower_esgs_io_to_mem.c
index 9cd7f4d6f9b..70aad36106f 100644
--- a/src/amd/common/ac_nir_lower_esgs_io_to_mem.c
+++ b/src/amd/common/ac_nir_lower_esgs_io_to_mem.c
@@ -124,6 +124,38 @@ lower_es_output_store(nir_builder *b,
    if (intrin->intrinsic != nir_intrinsic_store_output)
       return false;
 
+   /* 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.
+    *
+    * Vulkan spec 15.7 Built-In Variables:
+    *
+    *   The last active pre-rasterization shader stage (in pipeline order)
+    *   controls the Layer that is used. Outputs in previous shader stages
+    *   are not used, even if the last stage fails to write the Layer.
+    *
+    *   The last active pre-rasterization shader stage (in pipeline order)
+    *   controls the ViewportIndex that is used. Outputs in previous shader
+    *   stages are not used, even if the last stage fails to write the
+    *   ViewportIndex.
+    *
+    * So writes to those outputs in ES are simply ignored.
+    */
+   unsigned semantic = nir_intrinsic_io_semantics(intrin).location;
+   if (semantic == VARYING_SLOT_LAYER || semantic == VARYING_SLOT_VIEWPORT) {
+      nir_instr_remove(instr);
+      return true;
+   }
+
    lower_esgs_io_state *st = (lower_esgs_io_state *) state;
    unsigned write_mask = nir_intrinsic_write_mask(intrin);