ir3: Run divergence analysis at the end

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28573>

src/freedreno/ir3/ir3_compiler.c

@@ -124,6 +124,8 @@ static const nir_shader_compiler_options ir3_base_options = {
 
    .lower_int64_options = (nir_lower_int64_options)~0,
    .lower_doubles_options = (nir_lower_doubles_options)~0,
+
+   .divergence_analysis_options = nir_divergence_uniform_load_tears,
 };
 
 struct ir3_compiler *

src/freedreno/ir3/ir3_compiler_nir.c

@@ -3569,6 +3569,16 @@ emit_phi(struct ir3_context *ctx, nir_phi_instr *nphi)
 
    dst = ir3_get_def(ctx, &nphi->def, 1);
 
+   if (exec_list_is_singular(&nphi->srcs)) {
+      nir_phi_src *src = list_entry(exec_list_get_head(&nphi->srcs),
+                                    nir_phi_src, node);
+      if (nphi->def.divergent == src->src.ssa->divergent) {
+         dst[0] = ir3_get_src(ctx, &src->src)[0];
+         ir3_put_def(ctx, &nphi->def);
+         return;
+      }
+   }
+
    phi = ir3_instr_create(ctx->block, OPC_META_PHI, 1,
                           exec_list_length(&nphi->srcs));
    __ssa_dst(phi);

src/freedreno/ir3/ir3_context.c

@@ -120,8 +120,15 @@ ir3_context_init(struct ir3_compiler *compiler, struct ir3_shader *shader,
    if ((so->type == MESA_SHADER_FRAGMENT) && compiler->has_fs_tex_prefetch)
       NIR_PASS_V(ctx->s, ir3_nir_lower_tex_prefetch);
 
+   NIR_PASS(progress, ctx->s, nir_convert_to_lcssa, true, true);
+
    NIR_PASS(progress, ctx->s, nir_lower_phis_to_scalar, true);
 
+   /* This has to go at the absolute end to make sure that all SSA defs are
+    * correctly marked.
+    */
+   NIR_PASS_V(ctx->s, nir_divergence_analysis);
+
    /* Super crude heuristic to limit # of tex prefetch in small
     * shaders.  This completely ignores loops.. but that's really
     * not the worst of it's problems.  (A frag shader that has