Added support for ``if __debug__:'' -- if -O is given, this form is

recognized by the code generator and code generation for the test and
the subsequent suite is suppressed.

One must write *exactly* ``if __debug__:'' or ``elif __debug__:'' --
no parentheses or operators must be present, or the optimization is
not carried through.  Whitespace doesn't matter.  Other uses of
__debug__ will find __debug__ defined as 0 or 1 in the __builtin__
module.

diff --git a/Python/compile.c b/Python/compile.c
index b4377ec98a693cf264e23bc99539dc03660bec16..36c78aa801bb73dfab27899625c645e84ee11983 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1891,6 +1891,7 @@ com_assign(c, n, assigning)
                }
        }
 }
+
 /* Forward */ static node *get_rawdocstring PROTO((node *));
 
 static void
@@ -2170,6 +2171,90 @@ com_exec_stmt(c, n)
        com_pop(c, 3);
 }
 
+static int
+is_constant_false(c, n)
+       struct compiling *c;
+       node *n;
+{
+       object *v;
+       int i;
+
+  /* Label to avoid tail recursion */
+  next:
+       switch (TYPE(n)) {
+
+       case suite:
+               if (NCH(n) == 1) {
+                       n = CHILD(n, 0);
+                       goto next;
+               }
+               /* Fall through */
+       case file_input:
+               for (i = 0; i < NCH(n); i++) {
+                       node *ch = CHILD(n, i);
+                       if (TYPE(ch) == stmt) {
+                               n = ch;
+                               goto next;
+                       }
+               }
+               break;
+
+       case stmt:
+       case simple_stmt:
+       case small_stmt:
+               n = CHILD(n, 0);
+               goto next;
+
+       case expr_stmt:
+       case testlist:
+       case test:
+       case and_test:
+       case not_test:
+       case comparison:
+       case expr:
+       case xor_expr:
+       case and_expr:
+       case shift_expr:
+       case arith_expr:
+       case term:
+       case factor:
+       case power:
+       case atom:
+               if (NCH(n) == 1) {
+                       n = CHILD(n, 0);
+                       goto next;
+               }
+               break;
+
+       case NAME:
+               if (Py_OptimizeFlag && strcmp(STR(n), "__debug__") == 0)
+                       return 1;
+               break;
+
+       case NUMBER:
+               v = parsenumber(c, STR(n));
+               if (v == NULL) {
+                       err_clear();
+                       break;
+               }
+               i = testbool(v);
+               DECREF(v);
+               return i == 0;
+
+       case STRING:
+               v = parsestrplus(n);
+               if (v == NULL) {
+                       err_clear();
+                       break;
+               }
+               i = testbool(v);
+               DECREF(v);
+               return i == 0;
+
+       }
+       return 0;
+}
+
 static void
 com_if_stmt(c, n)
        struct compiling *c;
@@ -2182,9 +2267,11 @@ com_if_stmt(c, n)
        for (i = 0; i+3 < NCH(n); i+=4) {
                int a = 0;
                node *ch = CHILD(n, i+1);
+               if (is_constant_false(c, ch))
+                       continue;
                if (i > 0)
                        com_addoparg(c, SET_LINENO, ch->n_lineno);
-               com_node(c, CHILD(n, i+1));
+               com_node(c, ch);
                com_addfwref(c, JUMP_IF_FALSE, &a);
                com_addbyte(c, POP_TOP);
                com_pop(c, 1);
@@ -2196,7 +2283,8 @@ com_if_stmt(c, n)
        }
        if (i+2 < NCH(n))
                com_node(c, CHILD(n, i+2));
-       com_backpatch(c, anchor);
+       if (anchor)
+               com_backpatch(c, anchor);
 }
 
 static void