anv: Remove FS executables when applying the null FS optimization

If the executables are still hanging out,
anv_GetPipelineExecutableStatisticsKHR will try to dereference NULL
pointers in pipeline->shaders[MESA_SHADER_FRAGMENT].

At least in terms of fossil-db output, this matches the behavior from
before 73b3efcd59.

Fixes: 73b3efcd59 ("anv: Handle the null FS optimization after compiling shaders")
Closes: #6590
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16898>
(cherry picked from commit 65d6708bc3)

.pick_status.json

@@ -1147,7 +1147,7 @@
         "description": "anv: Remove FS executables when applying the null FS optimization",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "73b3efcd59ade6b9dc8c4cce994d7fbe5c1f0cac"
     },

src/intel/vulkan/anv_pipeline.c

@@ -1868,6 +1868,25 @@ done:
          anv_shader_bin_unref(pipeline->base.device, fs);
          pipeline->shaders[MESA_SHADER_FRAGMENT] = NULL;
          pipeline->active_stages &= ~VK_SHADER_STAGE_FRAGMENT_BIT;
+
+         /* The per-SIMD size fragment shaders should be last in the
+          * executables array.  Remove all of them.
+          */
+         ASSERTED unsigned removed = 0;
+
+         util_dynarray_foreach_reverse(&pipeline->base.executables,
+                                       struct anv_pipeline_executable,
+                                       tail) {
+            /* There must be at least one fragment shader. */
+            assert(removed > 0 || tail->stage == MESA_SHADER_FRAGMENT);
+
+            if (tail->stage != MESA_SHADER_FRAGMENT)
+               break;
+
+            (void) util_dynarray_pop(&pipeline->base.executables,
+                                     struct anv_pipeline_executable);
+            removed++;
+         }
       }
    }