nir: Free instructions more often

Soon we'll be allocating instructions out of a per-shader pool, which
means that if we don't free too many instructions during the main
optimization loop, the final nir_sweep() call will create holes which
can't be filled. By freeing instructions more aggressively, we can
allocate more instructions from the freelist which will reduce the final
memory usage.

Modified from Connor Abbott's original patch to rebase on top of
refactored DCE and so that the use-after-free in nir_algebraic_impl() is
fixed.

Co-authored-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12910>

diff --git a/src/compiler/nir/nir_opt_dce.c b/src/compiler/nir/nir_opt_dce.c
index 49e7ac0..1f4b0b3 100644 (file)
--- a/src/compiler/nir/nir_opt_dce.c
+++ b/src/compiler/nir/nir_opt_dce.c
@@ -107,7 +107,8 @@ struct loop_state {
 };
 
 static bool
-dce_block(nir_block *block, BITSET_WORD *defs_live, struct loop_state *loop)
+dce_block(nir_block *block, BITSET_WORD *defs_live, struct loop_state *loop,
+          struct exec_list *dead_instrs)
 {
    bool progress = false;
    bool phis_changed = false;
@@ -131,6 +132,7 @@ dce_block(nir_block *block, BITSET_WORD *defs_live, struct loop_state *loop)
          instr->pass_flags = live;
       } else if (!live) {
          nir_instr_remove(instr);
+         exec_list_push_tail(dead_instrs, &instr->node);
          progress = true;
       }
    }
@@ -146,20 +148,20 @@ dce_block(nir_block *block, BITSET_WORD *defs_live, struct loop_state *loop)
 
 static bool
 dce_cf_list(struct exec_list *cf_list, BITSET_WORD *defs_live,
-            struct loop_state *parent_loop)
+            struct loop_state *parent_loop, struct exec_list *dead_instrs)
 {
    bool progress = false;
    foreach_list_typed_reverse(nir_cf_node, cf_node, node, cf_list) {
       switch (cf_node->type) {
       case nir_cf_node_block: {
          nir_block *block = nir_cf_node_as_block(cf_node);
-         progress |= dce_block(block, defs_live, parent_loop);
+         progress |= dce_block(block, defs_live, parent_loop, dead_instrs);
          break;
       }
       case nir_cf_node_if: {
          nir_if *nif = nir_cf_node_as_if(cf_node);
-         progress |= dce_cf_list(&nif->else_list, defs_live, parent_loop);
-         progress |= dce_cf_list(&nif->then_list, defs_live, parent_loop);
+         progress |= dce_cf_list(&nif->else_list, defs_live, parent_loop, dead_instrs);
+         progress |= dce_cf_list(&nif->then_list, defs_live, parent_loop, dead_instrs);
          mark_src_live(&nif->condition, defs_live);
          break;
       }
@@ -176,7 +178,7 @@ dce_cf_list(struct exec_list *cf_list, BITSET_WORD *defs_live,
          struct set *predecessors = nir_loop_first_block(loop)->predecessors;
          if (predecessors->entries == 1 &&
              _mesa_set_next_entry(predecessors, NULL)->key == inner_state.preheader) {
-            progress |= dce_cf_list(&loop->body, defs_live, parent_loop);
+            progress |= dce_cf_list(&loop->body, defs_live, parent_loop, dead_instrs);
             break;
          }
 
@@ -185,7 +187,7 @@ dce_cf_list(struct exec_list *cf_list, BITSET_WORD *defs_live,
             /* dce_cf_list() resets inner_state.header_phis_changed itself, so
              * it doesn't have to be done here.
              */
-            dce_cf_list(&loop->body, defs_live, &inner_state);
+            dce_cf_list(&loop->body, defs_live, &inner_state, dead_instrs);
          } while (inner_state.header_phis_changed);
 
          /* We don't know how many times mark_cf_list() will repeat, so
@@ -199,6 +201,7 @@ dce_cf_list(struct exec_list *cf_list, BITSET_WORD *defs_live,
                nir_foreach_instr_safe(instr, block) {
                   if (!instr->pass_flags) {
                      nir_instr_remove(instr);
+                     exec_list_push_tail(dead_instrs, &instr->node);
                      progress = true;
                   }
                }
@@ -222,12 +225,17 @@ nir_opt_dce_impl(nir_function_impl *impl)
    BITSET_WORD *defs_live = rzalloc_array(NULL, BITSET_WORD,
                                           BITSET_WORDS(impl->ssa_alloc));
 
+   struct exec_list dead_instrs;
+   exec_list_make_empty(&dead_instrs);
+
    struct loop_state loop;
    loop.preheader = NULL;
-   bool progress = dce_cf_list(&impl->body, defs_live, &loop);
+   bool progress = dce_cf_list(&impl->body, defs_live, &loop, &dead_instrs);
 
    ralloc_free(defs_live);
 
+   nir_instr_free_list(&dead_instrs);
+
    if (progress) {
       nir_metadata_preserve(impl, nir_metadata_block_index |
                                   nir_metadata_dominance);

diff --git a/src/compiler/nir/nir_search.c b/src/compiler/nir/nir_search.c
index 4fd7ad6..6ff44f9 100644 (file)
--- a/src/compiler/nir/nir_search.c
+++ b/src/compiler/nir/nir_search.c
@@ -685,14 +685,15 @@ nir_algebraic_update_automaton(nir_instr *new_instr,
    nir_instr_worklist_destroy(automaton_worklist);
 }
 
-nir_ssa_def *
+static nir_ssa_def *
 nir_replace_instr(nir_builder *build, nir_alu_instr *instr,
                   struct hash_table *range_ht,
                   struct util_dynarray *states,
                   const nir_algebraic_table *table,
                   const nir_search_expression *search,
                   const nir_search_value *replace,
-                  nir_instr_worklist *algebraic_worklist)
+                  nir_instr_worklist *algebraic_worklist,
+                  struct exec_list *dead_instrs)
 {
    uint8_t swizzle[NIR_MAX_VEC_COMPONENTS] = { 0 };
 
@@ -803,7 +804,10 @@ nir_replace_instr(nir_builder *build, nir_alu_instr *instr,
     * that the instr may be in the worklist still, so we can't free it
     * directly.
     */
+   assert(instr->instr.pass_flags == 0);
+   instr->instr.pass_flags = 1;
    nir_instr_remove(&instr->instr);
+   exec_list_push_tail(dead_instrs, &instr->instr.node);
 
    return ssa_val;
 }
@@ -865,7 +869,8 @@ nir_algebraic_instr(nir_builder *build, nir_instr *instr,
                     const bool *condition_flags,
                     const nir_algebraic_table *table,
                     struct util_dynarray *states,
-                    nir_instr_worklist *worklist)
+                    nir_instr_worklist *worklist,
+                    struct exec_list *dead_instrs)
 {
 
    if (instr->type != nir_instr_type_alu)
@@ -891,7 +896,7 @@ nir_algebraic_instr(nir_builder *build, nir_instr *instr,
           !(table->values[xform->search].expression.inexact && ignore_inexact) &&
           nir_replace_instr(build, alu, range_ht, states, table,
                             &table->values[xform->search].expression,
-                            &table->values[xform->replace].value, worklist)) {
+                            &table->values[xform->replace].value, worklist, dead_instrs)) {
          _mesa_hash_table_clear(range_ht, NULL);
          return true;
       }
@@ -938,25 +943,31 @@ nir_algebraic_impl(nir_function_impl *impl,
     */
    nir_foreach_block_reverse(block, impl) {
       nir_foreach_instr_reverse(instr, block) {
+         instr->pass_flags = 0;
          if (instr->type == nir_instr_type_alu)
             nir_instr_worklist_push_tail(worklist, instr);
       }
    }
 
+   struct exec_list dead_instrs;
+   exec_list_make_empty(&dead_instrs);
+
    nir_instr *instr;
    while ((instr = nir_instr_worklist_pop_head(worklist))) {
       /* The worklist can have an instr pushed to it multiple times if it was
        * the src of multiple instrs that also got optimized, so make sure that
        * we don't try to re-optimize an instr we already handled.
        */
-      if (exec_node_is_tail_sentinel(&instr->node))
+      if (instr->pass_flags)
          continue;
 
       progress |= nir_algebraic_instr(&build, instr,
                                       range_ht, condition_flags,
-                                      table, &states, worklist);
+                                      table, &states, worklist, &dead_instrs);
    }
 
+   nir_instr_free_list(&dead_instrs);
+
    nir_instr_worklist_destroy(worklist);
    ralloc_free(range_ht);
    util_dynarray_fini(&states);

diff --git a/src/compiler/nir/nir_search.h b/src/compiler/nir/nir_search.h
index ba113f1..48777b4 100644 (file)
--- a/src/compiler/nir/nir_search.h
+++ b/src/compiler/nir/nir_search.h
@@ -237,14 +237,6 @@ NIR_DEFINE_CAST(nir_search_value_as_expression, nir_search_value,
                 nir_search_expression, value,
                 type, nir_search_value_expression)
 
-nir_ssa_def *
-nir_replace_instr(struct nir_builder *b, nir_alu_instr *instr,
-                  struct hash_table *range_ht,
-                  struct util_dynarray *states,
-                  const nir_algebraic_table *table,
-                  const nir_search_expression *search,
-                  const nir_search_value *replace,
-                  nir_instr_worklist *algebraic_worklist);
 bool
 nir_algebraic_impl(nir_function_impl *impl,
                    const bool *condition_flags,