nir: make divergence information metadata

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30814>

src/compiler/nir/nir.h

@@ -3317,6 +3317,22 @@ typedef enum {
     */
    nir_metadata_instr_index = 0x20,
 
+   /** Indicates that divergence analysis information is valid.
+    *
+    * This includes:
+    *   - nir_def::divergent
+    *   - nir_def::loop_invariant
+    *   - nir_block::divergent
+    *   - nir_loop::divergent_break
+    *   - nir_loop::divergent_continue
+    *
+    * A pass can preserve this metadata type if it never adds any instructions or
+    * moves them across loop breaks, as well as if it only removes instructions.
+    * CF modifications usually invalidate this metadata.  Most passes
+    * shouldn't preserve this metadata type.
+    */
+   nir_metadata_divergence = 0x40,
+
    /** All control flow metadata
     *
     * This includes all metadata preserved by a pass that preserves control flow

src/compiler/nir/nir_divergence_analysis.c

@@ -1448,17 +1448,19 @@ nir_divergence_analysis_impl(nir_function_impl *impl, nir_divergence_options opt
 
    visit_cf_list(&impl->body, &state);
 
-   nir_metadata_preserve(impl, nir_metadata_all);
+   /* Unless this pass is called with shader->options->divergence_analysis_options,
+    * it invalidates nir_metadata_divergence.
+    */
+   nir_metadata_preserve(impl, ~nir_metadata_divergence);
 }
 
 void
 nir_divergence_analysis(nir_shader *shader)
 {
-   shader->info.divergence_analysis_run = true;
    nir_foreach_function_impl(impl, shader) {
-      nir_divergence_analysis_impl(impl,
-                                   shader->options->divergence_analysis_options);
+      nir_metadata_require(impl, nir_metadata_divergence);
    }
+   shader->info.divergence_analysis_run = true;
 }
 
 /* Compute divergence between vertices of the same primitive. This uses
@@ -1484,7 +1486,7 @@ nir_vertex_divergence_analysis(nir_shader *shader)
       nir_metadata_require(impl, nir_metadata_block_index);
       state.impl = impl;
       visit_cf_list(&impl->body, &state);
-      nir_metadata_preserve(impl, nir_metadata_all);
+      nir_metadata_preserve(impl, nir_metadata_all & ~nir_metadata_divergence);
    }
 }
 

src/compiler/nir/nir_metadata.c

@@ -40,6 +40,9 @@ nir_metadata_require(nir_function_impl *impl, nir_metadata required, ...)
       nir_calc_dominance_impl(impl);
    if (NEEDS_UPDATE(nir_metadata_live_defs))
       nir_live_defs_impl(impl);
+   if (NEEDS_UPDATE(nir_metadata_divergence))
+      nir_divergence_analysis_impl(impl,
+                                   impl->function->shader->options->divergence_analysis_options);
    if (required & nir_metadata_loop_analysis) {
       va_list ap;
       va_start(ap, required);