Hi!
The problem here is that for loops that have constant 0/false condition
the C++ FE wants to correctly emit if (0) { body; incr-expr; }
but doesn't just build3 (COND_EXPR, ...), but fold_build3, and COND_EXPR
folding with constant condition optimizes away the unused branch completely
if it doesn't contain any labels. In this case it doesn't contain any
labels, but contains CASE_LABEL_EXPR that we should also take into account
(but can ignore it when during the walk we are inside a SWITCH_BODY).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/7.3?
2017-12-23 Jakub Jelinek <ja...@redhat.com>
PR c++/83553
* fold-const.c (struct contains_label_data): New type.
(contains_label_1): Return non-NULL even for CASE_LABEL_EXPR, unless
inside of a SWITCH_BODY seen during the walk.
(contains_label_p): Use walk_tree instead of
walk_tree_without_duplicates, prepare data for contains_label_1 and
provide own pset.
* c-c++-common/torture/pr83553.c: New test.
--- gcc/fold-const.c.jj 2017-12-21 09:43:17.000000000 +0100
+++ gcc/fold-const.c 2017-12-23 00:22:54.447669504 +0100
@@ -11218,22 +11218,48 @@ fold_binary_loc (location_t loc, enum tr
} /* switch (code) */
}
+/* Used by contains_label_[p1]. */
+
+struct contains_label_data
+{
+ hash_set<tree> *pset;
+ bool inside_switch_p;
+};
+
/* Callback for walk_tree, looking for LABEL_EXPR. Return *TP if it is
- a LABEL_EXPR; otherwise return NULL_TREE. Do not check the subtrees
- of GOTO_EXPR. */
+ a LABEL_EXPR or CASE_LABEL_EXPR not inside of another SWITCH_EXPR; otherwise
+ return NULL_TREE. Do not check the subtrees of GOTO_EXPR. */
static tree
-contains_label_1 (tree *tp, int *walk_subtrees, void *data ATTRIBUTE_UNUSED)
+contains_label_1 (tree *tp, int *walk_subtrees, void *data)
{
+ contains_label_data *d = (contains_label_data *) data;
switch (TREE_CODE (*tp))
{
case LABEL_EXPR:
return *tp;
+ case CASE_LABEL_EXPR:
+ if (!d->inside_switch_p)
+ return *tp;
+ return NULL_TREE;
+
+ case SWITCH_EXPR:
+ if (!d->inside_switch_p)
+ {
+ if (walk_tree (&SWITCH_COND (*tp), contains_label_1, data, d->pset))
+ return *tp;
+ d->inside_switch_p = true;
+ if (walk_tree (&SWITCH_BODY (*tp), contains_label_1, data, d->pset))
+ return *tp;
+ d->inside_switch_p = false;
+ *walk_subtrees = 0;
+ }
+ return NULL_TREE;
+
case GOTO_EXPR:
*walk_subtrees = 0;
-
- /* fall through */
+ return NULL_TREE;
default:
return NULL_TREE;
@@ -11246,8 +11272,9 @@ contains_label_1 (tree *tp, int *walk_su
static bool
contains_label_p (tree st)
{
- return
- (walk_tree_without_duplicates (&st, contains_label_1 , NULL) != NULL_TREE);
+ hash_set<tree> pset;
+ contains_label_data data = { &pset, false };
+ return walk_tree (&st, contains_label_1, &data, &pset) != NULL_TREE;
}
/* Fold a ternary expression of code CODE and type TYPE with operands
--- gcc/testsuite/c-c++-common/torture/pr83553.c.jj 2017-12-23
00:30:20.548180122 +0100
+++ gcc/testsuite/c-c++-common/torture/pr83553.c 2017-12-23
00:29:11.000000000 +0100
@@ -0,0 +1,29 @@
+/* PR c++/83553 */
+/* { dg-do run } */
+
+int a[3];
+
+int
+foo (int n)
+{
+ switch (n)
+ {
+ case 0:
+ for (n = 7, a[0]++; 0; a[2] = a[1] + 1)
+ {
+ case 2:
+ a[1] = a[0] + 1;
+ }
+ }
+ return n;
+}
+
+int
+main ()
+{
+ if (foo (0) != 7 || a[0] != 1 || a[1] || a[2])
+ __builtin_abort ();
+ if (foo (2) != 2 || a[0] != 1 || a[1] != 2 || a[2] != 3)
+ __builtin_abort ();
+ return 0;
+}
Jakub
