Optimize away stores to variables that are never read

1 files changed, 76 insertions, 9 deletions

diff --git a/optimize.c b/optimize.c
index ccb11d7..508f5e6 100644
--- a/optimize.c
+++ b/optimize.c
@@ -402,21 +402,35 @@ peephole (node_t *node,
 
 	*changed = TRUE;
     }
+    else if (node_is (node0, NODE_STORE)	&&
+	     !node0->store.definition->used)
+    {
+	node0->common.type = NODE_POP;
+
+	*changed = TRUE;
+    }
+    else if (node_is (node0, NODE_STORE_IND)	&&
+	     !node0->store_ind.definition->used)
+    {
+	node0->common.type = NODE_POP;
+
+	*changed = TRUE;
+    }
 
     node->common.next = peephole (node->common.next, changed);
 
     return node;
 }
 
-gboolean
-optimize (ast_t *ast)
+static void
+do_optimize (ast_t *ast, gboolean *changed)
 {
     GList *list;
     node_t **node = NULL;
     node_t **entry = NULL;
 
     for (list = ast->common.children->head; list != NULL; list = list->next)
-	optimize (list->data);
+	do_optimize (list->data, changed);
 
     if (ast_is (ast, AST_PROGRAM, 0))
     {
@@ -430,22 +444,75 @@ optimize (ast_t *ast)
 
 	entry = &(function->enter);
     }
-
+    
     if (entry)
     {
-	gboolean changed;
+	gboolean c;
 
 	node = entry;
 
 	do
 	{
-	    changed = FALSE;
+	    c = FALSE;
+	    
+	    *node = peephole (*node, &c);
+	    *node = remove_nops (*node, &c);
 
-	    *node = peephole (*node, &changed);
-	    *node = remove_nops (*node, &changed);
+	    if (c)
+		*changed = TRUE;
 	}
-	while (changed);
+	while (c);
     }
+}
+
+static void
+mark_variables_unused (ast_t *ast)
+{
+    GList *list;
+
+    for (list = ast->common.children->head; list != NULL; list = list->next)
+	mark_variables_unused (list->data);
+
+    if (ast_is (ast, AST_DEFINITION, AST_VARIABLE_DEFINITION))
+    {
+	ast_variable_definition_t *variable = &ast->definition.variable;
+
+	variable->used = FALSE;
+    }
+}
+
+static void
+mark_used (node_t *node, gpointer data)
+{
+    if (node->common.type == NODE_LOAD)
+    {
+	node->load.definition->used = TRUE;
+    }
+    else if (node->common.type == NODE_LOAD_IND)
+    {
+	node->load_ind.definition->used = TRUE;
+    }
+}
+
+gboolean
+optimize (ast_t *ast)
+{
+    gboolean changed;
+
+    do
+    {
+	changed = FALSE;
+
+	mark_variables_unused (ast);
+	node_breadth_first (ast->program.enter, mark_used, NULL);
+	
+	do_optimize (ast, &changed);
+    } while (changed);
 
+    /* The offsets pass also uses the "used" field in
+     * ast_variable_definition_t, and it expects it
+     * to start out as FALSE, so clear it here.
+     */
+    mark_variables_unused (ast);
     return TRUE;
 }