spirv: Mark phis as mediump instead of directly lowering them to 16 bit.

This reverts commit 6f25d45877a1e1a7ac6250a7d051d33485e0cba7, replacing it
with GLSL_PRECISION_MEDIUM.  The previous commit ended up not being the
right approach, as it affected only nir vars for spirv phis and not other
nir vars, and we want a tool that does both.  The new
nir_lower_mediump_vars pass can do that for you.

No fossil-db change for my angle fossils run on radv.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18259>
(cherry picked from commit e1588cdf9ecc26c51ae0df3a380e1ac781e41941)

2 files changed, 9 insertions, 33 deletions

diff --git a/.pick_status.json b/.pick_status.json
index 019c63272c9..6b4e8f7d8b0 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -6196,7 +6196,7 @@
         "description": "spirv: Mark phis as mediump instead of directly lowering them to 16 bit.",
         "nominated": true,
         "nomination_type": 2,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "6f25d45877a1e1a7ac6250a7d051d33485e0cba7"
     },
diff --git a/src/compiler/spirv/vtn_cfg.c b/src/compiler/spirv/vtn_cfg.c
index 9f1853befbe..4b1d66550b3 100644
--- a/src/compiler/spirv/vtn_cfg.c
+++ b/src/compiler/spirv/vtn_cfg.c
@@ -921,34 +921,18 @@ vtn_handle_phis_first_pass(struct vtn_builder *b, SpvOp opcode,
     * algorithm all over again.  It's easier if we just let
     * lower_vars_to_ssa do that for us instead of repeating it here.
     */
-   bool relaxed_precision = false;
-   if (b->options->mediump_16bit_alu) {
-      struct vtn_value *phi_val = vtn_untyped_value(b, w[2]);
-      relaxed_precision = vtn_value_is_relaxed_precision(b, phi_val);
-   }
+   struct vtn_type *type = vtn_get_type(b, w[1]);
+   nir_variable *phi_var =
+      nir_local_variable_create(b->nb.impl, type->type, "phi");
 
-   const struct glsl_type *dest_type = vtn_get_type(b, w[1])->type;
-   const struct glsl_type *type = dest_type;
-   if (relaxed_precision) {
-      if (glsl_get_base_type(type) == GLSL_TYPE_FLOAT)
-         type = glsl_float16_type(type);
-      else if (glsl_get_base_type(type) == GLSL_TYPE_INT)
-         type = glsl_int16_type(type);
-      else if (glsl_get_base_type(type) == GLSL_TYPE_UINT)
-         type = glsl_uint16_type(type);
-   }
+   struct vtn_value *phi_val = vtn_untyped_value(b, w[2]);
+   if (vtn_value_is_relaxed_precision(b, phi_val))
+      phi_var->data.precision = GLSL_PRECISION_MEDIUM;
 
-   nir_variable *phi_var = nir_local_variable_create(b->nb.impl, type, "phi");
    _mesa_hash_table_insert(b->phi_table, w, phi_var);
 
-   struct vtn_ssa_value *dest =
-      vtn_local_load(b, nir_build_deref_var(&b->nb, phi_var), 0);
-
-   if (relaxed_precision) {
-      dest->type = dest_type;
-      vtn_mediump_upconvert_value(b, dest);
-   }
-   vtn_push_ssa_value(b, w[2], dest);
+   vtn_push_ssa_value(b, w[2],
+      vtn_local_load(b, nir_build_deref_var(&b->nb, phi_var), 0));
 
    return true;
 }
@@ -969,12 +953,6 @@ vtn_handle_phi_second_pass(struct vtn_builder *b, SpvOp opcode,
    if (phi_entry == NULL)
       return true;
 
-   bool relaxed_precision = false;
-   if (b->options->mediump_16bit_alu) {
-      struct vtn_value *phi_val = vtn_untyped_value(b, w[2]);
-      relaxed_precision = vtn_value_is_relaxed_precision(b, phi_val);
-   }
-
    nir_variable *phi_var = phi_entry->data;
 
    for (unsigned i = 3; i < count; i += 2) {
@@ -988,8 +966,6 @@ vtn_handle_phi_second_pass(struct vtn_builder *b, SpvOp opcode,
       b->nb.cursor = nir_after_instr(&pred->end_nop->instr);
 
       struct vtn_ssa_value *src = vtn_ssa_value(b, w[i]);
-      if (relaxed_precision)
-         src = vtn_mediump_downconvert_value(b, src);
 
       vtn_local_store(b, src, nir_build_deref_var(&b->nb, phi_var), 0);
    }