v3d: Stop advertising support for HW clip planes.

The GL frontend is perfectly good at lowering it like we do.  Cuts out a
bunch of duplicate code.

We still have ucp_enables for the FS due to lowering of CLIPDIST to
discards in the FS.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8953>

src/broadcom/compiler/nir_to_vir.c

@@ -3536,15 +3536,6 @@ ntq_emit_intrinsic(struct v3d_compile *c, nir_intrinsic_instr *instr)
                                           nir_src_comp_as_uint(instr->src[0], 0)));
                 break;
 
-        case nir_intrinsic_load_user_clip_plane:
-                for (int i = 0; i < nir_intrinsic_dest_components(instr); i++) {
-                        ntq_store_def(c, &instr->def, i,
-                                      vir_uniform(c, QUNIFORM_USER_CLIP_PLANE,
-                                                  nir_intrinsic_ucp_id(instr) *
-                                                  4 + i));
-                }
-                break;
-
         case nir_intrinsic_load_viewport_x_scale:
                 ntq_store_def(c, &instr->def, 0,
                               vir_uniform(c, QUNIFORM_VIEWPORT_X_SCALE, 0));

src/broadcom/compiler/v3d_compiler.h

@@ -205,8 +205,6 @@ enum quniform_contents {
         QUNIFORM_VIEWPORT_Z_OFFSET,
         QUNIFORM_VIEWPORT_Z_SCALE,
 
-        QUNIFORM_USER_CLIP_PLANE,
-
         /**
          * A reference to a V3D 3.x texture config parameter 0 uniform.
          *
@@ -414,7 +412,6 @@ struct v3d_key {
          */
         uint32_t sampler_is_32b;
 
-        uint8_t ucp_enables;
         bool is_last_geometry_stage;
         bool robust_uniform_access;
         bool robust_storage_access;
@@ -437,6 +434,7 @@ struct v3d_fs_key {
         uint8_t swap_color_rb;
         /* Mask of which render targets need to be written as 32-bit floats */
         uint8_t f32_color_rb;
+        uint8_t ucp_enables;
 
         /* Color format information per render target. Only set when logic
          * operations are enabled, when fbfetch is in use or when falling back

src/broadcom/compiler/vir.c

@@ -1119,41 +1119,29 @@ v3d_nir_lower_fs_early(struct v3d_compile *c)
 static void
 v3d_nir_lower_gs_late(struct v3d_compile *c)
 {
-        if (c->key->ucp_enables) {
-                NIR_PASS(_, c->s, nir_lower_clip_gs, c->key->ucp_enables,
-                         true, NULL);
-        }
-
-        /* Note: GS output scalarizing must happen after nir_lower_clip_gs. */
         NIR_PASS(_, c->s, nir_lower_io_to_scalar, nir_var_shader_out, NULL, NULL);
 }
 
 static void
 v3d_nir_lower_vs_late(struct v3d_compile *c)
 {
-        if (c->key->ucp_enables) {
-                NIR_PASS(_, c->s, nir_lower_clip_vs, c->key->ucp_enables,
-                         false, true, NULL);
-                NIR_PASS(_, c->s, nir_lower_io_to_scalar,
-                         nir_var_shader_out, NULL, NULL);
-        }
-
-        /* Note: VS output scalarizing must happen after nir_lower_clip_vs. */
         NIR_PASS(_, c->s, nir_lower_io_to_scalar, nir_var_shader_out, NULL, NULL);
 }
 
 static void
 v3d_nir_lower_fs_late(struct v3d_compile *c)
 {
-        /* In OpenGL the fragment shader can't read gl_ClipDistance[], but
-         * Vulkan allows it, in which case the SPIR-V compiler will declare
-         * VARING_SLOT_CLIP_DIST0 as compact array variable. Pass true as
-         * the last parameter to always operate with a compact array in both
-         * OpenGL and Vulkan so we do't have to care about the API we
-         * are using.
+        /* If there are clip distance writes (either GL/Vulkan
+         * gl_ClipDistance[], or lowered user clip planes for desktop GL),
+         * then we need to emit the discards for them at the top of the fragment
+         * shader.
+         *
+         * The SPIR-V compiler will declare VARING_SLOT_CLIP_DIST0 as compact
+         * array variable, so we have GL's clip lowering follow suit
+         * (PIPE_CAP_NIR_COMPACT_ARRAYS).
          */
-        if (c->key->ucp_enables)
-                NIR_PASS(_, c->s, nir_lower_clip_fs, c->key->ucp_enables, true, false);
+        if (c->fs_key->ucp_enables)
+                NIR_PASS(_, c->s, nir_lower_clip_fs, c->fs_key->ucp_enables, true, false);
 
         NIR_PASS(_, c->s, nir_lower_io_to_scalar, nir_var_shader_in, NULL, NULL);
 }