radeonsi: declare prolog LINE_STIPPLE_TEX_ENA VGPR only if needed

Small PS have their VGPR usage equal to the number of input VGPRs,
and this reduces it.

1 input VGPR removed from the PS prolog in most cases.

src/gallium/drivers/radeonsi/si_shader.c

@@ -1748,6 +1748,8 @@ static void si_get_ps_prolog_key(struct si_shader *shader, union si_shader_part_
       G_0286CC_PERSP_CENTROID_ENA(shader->config.spi_ps_input_addr); /* addr because the PS prolog may use it */
    key->ps_prolog.uses_linear_centroid =
       G_0286CC_LINEAR_CENTROID_ENA(shader->config.spi_ps_input_addr); /* addr because the PS prolog may use it */
+   key->ps_prolog.reserve_line_stipple_tex_ena =
+      G_0286CC_LINE_STIPPLE_TEX_ENA(shader->config.spi_ps_input_addr); /* unused but may need to be reserved */
    key->ps_prolog.fragcoord_usage_mask =
       G_0286CC_POS_X_FLOAT_ENA(shader->config.spi_ps_input_ena) |
       (G_0286CC_POS_Y_FLOAT_ENA(shader->config.spi_ps_input_ena) << 1) |

src/gallium/drivers/radeonsi/si_shader.h

@@ -566,6 +566,7 @@ union si_shader_part_key {
       unsigned num_interp_inputs : 5; /* BCOLOR is at this location */
       unsigned uses_persp_centroid : 1;
       unsigned uses_linear_centroid : 1;
+      unsigned reserve_line_stipple_tex_ena : 1; /* only reserve the VGPR, don't use it */
       unsigned fragcoord_usage_mask : 4;
       unsigned uses_ancillary : 1;
       unsigned uses_sample_coverage : 1;

src/gallium/drivers/radeonsi/si_shader_args.c

@@ -684,7 +684,8 @@ void si_get_ps_prolog_args(struct si_shader_args *args,
    if (key->ps_prolog.uses_linear_centroid)
       ac_add_arg(&args->ac, AC_ARG_VGPR, 2, AC_ARG_VALUE, &args->ac.linear_centroid);
 
-   ac_add_arg(&args->ac, AC_ARG_VGPR, 1, AC_ARG_VALUE, &args->ac.line_stipple_tex_ena);
+   if (key->ps_prolog.reserve_line_stipple_tex_ena)
+      ac_add_arg(&args->ac, AC_ARG_VGPR, 1, AC_ARG_VALUE, &args->ac.line_stipple_tex_ena);
 
    /* POS_X|Y|Z|W_FLOAT */
    u_foreach_bit(i, key->ps_prolog.fragcoord_usage_mask)

src/gallium/drivers/radeonsi/si_shader_info.c

@@ -369,6 +369,10 @@ static void gather_instruction(const struct nir_shader *nir, struct si_shader_in
          if (intr->intrinsic == nir_intrinsic_load_barycentric_at_sample)
             info->uses_interp_at_sample = true;
          break;
+      case nir_intrinsic_load_frag_coord:
+         if (nir_def_components_read(&intr->def) & BITFIELD_BIT(3))
+            info->uses_sysval_frag_coord_w = true;
+         break;
       case nir_intrinsic_load_input:
       case nir_intrinsic_load_per_vertex_input:
       case nir_intrinsic_load_per_primitive_input:

src/gallium/drivers/radeonsi/si_shader_info.h

@@ -150,6 +150,7 @@ struct si_shader_info {
    bool uses_sysval_primitive_id;
    bool uses_sysval_front_face;
    bool uses_sysval_invocation_id;
+   bool uses_sysval_frag_coord_w;
    bool uses_atomic_ordered_add;
    bool writes_psize;
    bool writes_primid;

src/gallium/drivers/radeonsi/si_shader_variant_info.c

@@ -614,7 +614,6 @@ unsigned si_get_spi_ps_input_addr_for_prolog(struct si_shader_selector *sel)
                                 S_0286D0_PERSP_CENTER_ENA(1) |
                                 S_0286D0_LINEAR_SAMPLE_ENA(1) |
                                 S_0286D0_LINEAR_CENTER_ENA(1) |
-                                S_0286D0_LINE_STIPPLE_TEX_ENA(1) |
                                 S_0286D0_FRONT_FACE_ENA(1) |
                                 S_0286D0_POS_FIXED_PT_ENA(1);
 
@@ -627,6 +626,22 @@ unsigned si_get_spi_ps_input_addr_for_prolog(struct si_shader_selector *sel)
    if (sel->info.uses_sysval_linear_centroid)
       spi_ps_input_addr |= S_0286D0_LINEAR_CENTROID_ENA(1);
 
+   /* If barycentrics and pos.w aren't used, we may need LINE_STIPPLE_TEX_ENA as the filler
+    * input VGPR. See si_fixup_spi_ps_input_config for more information.
+    */
+   if (!sel->info.uses_sysval_persp_sample &&
+       !sel->info.uses_sysval_persp_center &&
+       !sel->info.uses_sysval_persp_centroid &&
+       !sel->info.uses_sysval_linear_sample &&
+       !sel->info.uses_sysval_linear_center &&
+       !sel->info.uses_sysval_linear_centroid &&
+       !sel->info.uses_interp_color &&
+       !sel->info.uses_sysval_frag_coord_w &&
+       /* We don't set LINE_STIPPLE_TEX_ENA with LLVM, and never on GFX12. */
+       sel->info.base.use_aco_amd &&
+       sel->screen->info.gfx_level != GFX12)
+      spi_ps_input_addr |= S_0286D0_LINE_STIPPLE_TEX_ENA(1);
+
    if (sel->info.uses_sysval_ancillary)
       spi_ps_input_addr |= S_0286D0_ANCILLARY_ENA(1);