On 11/29/2017 01:30 AM, Jakub Jelinek wrote:
On Tue, Nov 28, 2017 at 09:11:00PM -0700, Martin Sebor wrote:
On 11/27/2017 02:22 AM, Dominik Inführ wrote:
Thanks for all the reviews! I’ve revised the patch, the operator_delete_flag is
now stored in tree_decl_with_vis (there already seem to be some
FUNCTION_DECL-flags in there). I’ve also added the option -fallocation-dce to
disable this optimization. It bootstraps and no regressions on aarch64 and
x86_64.
It's great to be able to eliminate pairs of these calls. For
unpaired calls, though, I think it would be even more useful to
also issue a warning. Otherwise the elimination will mask bugs
?? I hope you're only talking about allocation where the returned
pointer can't leak elsewhere, doing allocation in one function
(e.g. constructor, or whatever other function) and deallocation in some
other one is so common such a warning would be not just useless, but
harmful with almost all occurrences being false positives.
Warning on malloc/standard operator new or malloc/realloc-like function
when the return pointer can't escape the current function is reasonable.
Yes, warn for leaks, or for calls to delete/free with no matching
new/malloc (when they can be detected).
From the test case included in the patch, warn on the first two
of the following three functions:
+++ b/gcc/testsuite/g++.dg/cpp1y/new1.C
@@ -0,0 +1,65 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce-details" } */
+
+#include <stdlib.h>
+
+void
+new_without_use() {
+ int *x = new int;
+}
+
+void
+new_array_without_use() {
+ int *x = new int[5];
+}
+
+void
+new_primitive() {
+ int *x = new int;
+ delete x;
+}
An obvious extension to such a checker would then be to also detect
possible invalid deallocations, as in:
void f (unsigned n)
{
void *p = n < 256 ? alloca (n) : malloc (n);
// ...
free (p);
}
David Malcolm was working on something like that earlier this year
so he might have some thoughts on this as well.
Martin
