nir: gather interpolation qualifiers

we'll want this to be able to link interpolation qualifiers in a simple way with
nir_opt_varyings. add the metadata for it and the FS gathering pass.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36501>

src/compiler/nir/nir_gather_info.c

@@ -573,6 +573,25 @@ gather_intrinsic_info(nir_intrinsic_instr *instr, nir_shader *shader,
          else
             shader->info.tess.tcs_cross_invocation_inputs_read |= slot_mask;
       }
+
+      if (shader->info.stage == MESA_SHADER_FRAGMENT &&
+          instr->intrinsic == nir_intrinsic_load_interpolated_input) {
+         nir_intrinsic_instr *bary = nir_src_as_intrinsic(instr->src[0]);
+
+         if (bary && nir_intrinsic_has_interp_mode(bary)) {
+            enum glsl_interp_mode mode = nir_intrinsic_interp_mode(bary);
+
+            if (mode == INTERP_MODE_NOPERSPECTIVE)
+               shader->info.linear_varyings |= slot_mask;
+            else
+               shader->info.perspective_varyings |= slot_mask;
+         } else {
+            /* If the driver is lowering barycentrics, we can't recover the
+             * interpolation qualifiers. Bail.
+             */
+            shader->info.known_interpolation_qualifiers = false;
+         }
+      }
       break;
 
    case nir_intrinsic_load_output:
@@ -1035,6 +1054,9 @@ nir_shader_gather_info(nir_shader *shader, nir_function_impl *entrypoint)
       shader->info.fs.uses_fbfetch_output = false;
       shader->info.fs.needs_coarse_quad_helper_invocations = false;
       shader->info.fs.needs_full_quad_helper_invocations = false;
+
+      /* By definition the fragment shader knows, unless we fail to gather. */
+      shader->info.known_interpolation_qualifiers = true;
    }
    if (shader->info.stage == MESA_SHADER_TESS_CTRL) {
       shader->info.tess.tcs_same_invocation_inputs_read = 0;

src/compiler/nir/nir_print.c

@@ -2676,6 +2676,8 @@ print_shader_info(const struct shader_info *info, FILE *fp)
    print_nz_x64(fp, "dual_slot_inputs", info->dual_slot_inputs);
    print_nz_x64(fp, "outputs_written", info->outputs_written);
    print_nz_x64(fp, "outputs_read", info->outputs_read);
+   print_nz_x64(fp, "perspective_varyings", info->perspective_varyings);
+   print_nz_x64(fp, "linear_varyings", info->linear_varyings);
 
    print_nz_bitset(fp, "system_values_read", info->system_values_read, ARRAY_SIZE(info->system_values_read));
 
@@ -2750,6 +2752,7 @@ print_shader_info(const struct shader_info *info, FILE *fp)
 
    print_nz_bool(fp, "first_ubo_is_default_ubo", info->first_ubo_is_default_ubo);
    print_nz_bool(fp, "separate_shader", info->separate_shader);
+   print_nz_bool(fp, "known_interpolation_qualifiers", info->known_interpolation_qualifiers);
    print_nz_bool(fp, "has_transform_feedback_varyings", info->has_transform_feedback_varyings);
    print_nz_bool(fp, "flrp_lowered", info->flrp_lowered);
    print_nz_bool(fp, "io_lowered", info->io_lowered);

src/compiler/shader_info.h

@@ -87,6 +87,12 @@ typedef struct shader_info {
    /* Which system values are actually read */
    BITSET_DECLARE(system_values_read, SYSTEM_VALUE_MAX);
 
+   /* If known_interpolation_qualifiers is set, bitsets mapping locations to
+    * interpolation qualifiers perspective/linear/flat.
+    */
+   uint64_t perspective_varyings;
+   uint64_t linear_varyings;
+
    /* Which I/O is per-primitive, for read/written information combine with
     * the fields above.
     */
@@ -202,6 +208,11 @@ typedef struct shader_info {
    /* Whether or not separate shader objects were used */
    bool separate_shader:1;
 
+   /* Whether perspective_varyings/linear_varyings can be trusted. This depends
+    * on what this shader was linked with, as well as the API.
+    */
+   bool known_interpolation_qualifiers:1;
+
    /** Was this shader linked with any transform feedback varyings? */
    bool has_transform_feedback_varyings:1;