Mesa (main): mesa/st: Fix iris regression with clip distances.

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Module: Mesa
Branch: main
Commit: a76ec17f12c39a88cf44e039a62ed74aca4a19f2
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=a76ec17f12c39a88cf44e039a62ed74aca4a19f2

Author: Emma Anholt <emma at anholt.net>
Date:   Tue May 18 16:57:30 2021 -0700

mesa/st: Fix iris regression with clip distances.

In general gallium shaders are all SSO and it's up to the driver to handle
lining up varying storage between stages at draw time.  However, there's a
NIR option "unify_interfaces" that iris uses which applies to non-SSO (as
indicated by nir->info.separate_shader) shaders and makes the inputs_read
and outputs_written match up at GLSL-to-NIR link time, and then iris then
avoids any lowering passes that would add new varyings.

By introducing info gathering after variant creation (because all I knew
was "gallium is always SSO"), I broke the unify_interfaces link-time setup
on iris.  Just skip that when the unify_interfaces flag is set, and add
some asserts to catch anyone trying to mix unify_interfaces with known
varying-adjusting lowering passes.

Closes: #4450
Reviewed-by: Dave Airlie <airlied at redhat.com>
Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10876>

---

 src/mesa/state_tracker/st_program.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/mesa/state_tracker/st_program.c b/src/mesa/state_tracker/st_program.c
index 99c81b8970a..9f4040e5d68 100644
--- a/src/mesa/state_tracker/st_program.c
+++ b/src/mesa/state_tracker/st_program.c
@@ -774,11 +774,14 @@ st_create_common_variant(struct st_context *st,
 
       state.type = PIPE_SHADER_IR_NIR;
       state.ir.nir = get_nir_shader(st, stp);
+      const nir_shader_compiler_options *options = ((nir_shader *)state.ir.nir)->options;
+
       if (key->clamp_color) {
          NIR_PASS_V(state.ir.nir, nir_lower_clamp_color_outputs);
          finalize = true;
       }
       if (key->passthrough_edgeflags) {
+         assert(!options->unify_interfaces);
          NIR_PASS_V(state.ir.nir, nir_lower_passthrough_edgeflags);
          finalize = true;
       }
@@ -806,6 +809,7 @@ st_create_common_variant(struct st_context *st,
       }
 
       if (key->lower_ucp) {
+         assert(!options->unify_interfaces);
          lower_ucp(st, state.ir.nir, key->lower_ucp, params);
          finalize = true;
       }
@@ -823,9 +827,18 @@ st_create_common_variant(struct st_context *st,
          st_finalize_nir(st, &stp->Base, stp->shader_program, state.ir.nir,
                          true, false);
 
-         /* Some of the lowering above may have introduced new varyings */
-         nir_shader_gather_info(state.ir.nir,
-                                nir_shader_get_entrypoint(state.ir.nir));
+         /* Clip lowering and edgeflags may have introduced new varyings, so
+          * update the inputs_read/outputs_written. However, with
+          * unify_interfaces set (aka iris) the non-SSO varyings layout is
+          * decided at link time with outputs_written updated so the two line
+          * up.  A driver with this flag set may not use any of the lowering
+          * passes that would change the varyings, so skip to make sure we don't
+          * break its linkage.
+          */
+         if (!options->unify_interfaces) {
+            nir_shader_gather_info(state.ir.nir,
+                                   nir_shader_get_entrypoint(state.ir.nir));
+         }
       }
 
       if (key->is_draw_shader)