glsl: switch ir_variable_refcount to linear_ctx

Compiling my shader-db with the gallium noop driver is 6.8% faster now.
Theoretical stat-based results are below, which don't always reflect real
results.

When compiling Heaven shaders with the gallium noop driver,
134610 calloc calls are removed.

134610 / ralloc count = 6%, so it's roughly the equivalent of 6% of
the cost of all ralloc calls that's removed. The shift from calloc to
linear_alloc increases ralloc calls by 0.4%, so the approximate reduction
is 6% -> 0.4% overhead change.

Acked-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Acked-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36539>

src/compiler/glsl/ir_variable_refcount.cpp

@@ -37,31 +37,15 @@
 
 ir_variable_refcount_visitor::ir_variable_refcount_visitor()
 {
-   this->mem_ctx = ralloc_context(NULL);
+   this->linalloc = linear_context(ralloc_context(NULL));
    this->ht = _mesa_pointer_hash_table_create(NULL);
    this->global = true;
 }
 
-static void
-free_entry(struct hash_entry *entry)
-{
-   ir_variable_refcount_entry *ivre = (ir_variable_refcount_entry *) entry->data;
-
-   /* Free assignment list */
-   ir_exec_node *n;
-   while ((n = ivre->assign_list.pop_head()) != NULL) {
-      struct assignment_entry *assignment_entry =
-         ir_exec_node_data(struct assignment_entry, n, link);
-      free(assignment_entry);
-   }
-
-   delete ivre;
-}
-
 ir_variable_refcount_visitor::~ir_variable_refcount_visitor()
 {
-   ralloc_free(this->mem_ctx);
-   _mesa_hash_table_destroy(this->ht, free_entry);
+   ralloc_free(ralloc_parent_of_linear_context(this->linalloc));
+   _mesa_hash_table_destroy(this->ht, NULL);
 }
 
 // constructor
@@ -83,7 +67,7 @@ ir_variable_refcount_visitor::get_variable_entry(ir_variable *var)
    if (e)
       return (ir_variable_refcount_entry *)e->data;
 
-   ir_variable_refcount_entry *entry = new ir_variable_refcount_entry(var);
+   ir_variable_refcount_entry *entry = new(linalloc) ir_variable_refcount_entry(var);
    assert(entry->referenced_count == 0);
    _mesa_hash_table_insert(this->ht, var, entry);
 
@@ -149,7 +133,8 @@ ir_variable_refcount_visitor::visit_leave(ir_assignment *ir)
       assert(entry->referenced_count >= entry->assigned_count);
       if (entry->referenced_count == entry->assigned_count) {
          struct assignment_entry *assignment_entry =
-            (struct assignment_entry *)calloc(1, sizeof(*assignment_entry));
+            (struct assignment_entry *)linear_zalloc(this->linalloc,
+                                                     struct assignment_entry);
          assignment_entry->assign = ir;
          entry->assign_list.push_head(&assignment_entry->link);
       }

src/compiler/glsl/ir_variable_refcount.h

@@ -44,6 +44,8 @@ struct assignment_entry {
 class ir_variable_refcount_entry
 {
 public:
+   DECLARE_LINEAR_ALLOC_CXX_OPERATORS(ir_variable_refcount_entry,,)
+
    ir_variable_refcount_entry(ir_variable *var);
 
    ir_variable *var; /* The key: the variable's pointer. */
@@ -90,7 +92,7 @@ public:
     */
    struct hash_table *ht;
 
-   void *mem_ctx;
+   linear_ctx *linalloc;
 
    bool global;
 };

src/compiler/glsl/opt_dead_code.cpp

@@ -96,7 +96,6 @@ do_dead_code(ir_exec_list *instructions)
                }
 
                assignment_entry->link.remove();
-               free(assignment_entry);
             }
             progress = true;
 	 }