| Summary: | [4.3 regression] warning not emitted when code expanded from macro | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Tom Tromey <tromey> |
| Component: | c++ | Assignee: | Jakub Jelinek <jakub> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | dodji, fang, fedora84, gcc-bugs |
| Priority: | P2 | Keywords: | diagnostic |
| Version: | 4.3.0 | ||
| Target Milestone: | 4.3.6 | ||
| URL: | http://gcc.gnu.org/ml/gcc-patches/2008-11/msg00361.html | ||
| See Also: | https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52961 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2008-11-10 13:53:26 | |
| Attachments: | candidate partial fix | ||
|
Description
Tom Tromey
2008-06-09 16:33:18 UTC
Confirmed. Created attachment 15984 [details]
candidate partial fix
This patch fixes the problem patially.
if you have:
------------
void
foo ()
{
#define WARNS while(0)
#define DOES_NOT_WARN while(0);
WARNS; // { dg-warning }
DOES_NOT_WARN;
while (0); // { dg-warning }
}
---------------
The compiler (augmented with the patch) says:
/home/dodji/devel/src/gcc-bug-test.cc:6: warning: suggest a space before ‘;’ or explicit braces around empty body in ‘while’ statement
/home/dodji/devel/src/gcc-bug-test.cc:8: warning: suggest a space before ‘;’ or explicit braces around empty body in ‘while’ statement
(In reply to comment #2) > void > foo () > { > #define WARNS while(0) > #define DOES_NOT_WARN while(0); > WARNS; // { dg-warning } > DOES_NOT_WARN; I don't think we want to warn here. Even if we have the right location of ')', this would be hard to warn. How do you distinguish? DOES_NOT_WARN; DOES_NOT_WARN/**/; That said, I don't think tracking the end of the macro is a good idea either. It just moves the problem around. Another workaround would be to not check close_paren.column + 1 == semicolon.column since it is the next token and before the semicolon there is no whitespace. The only problem is if there is a comment, such as while(0)/**/; and we have no way to track that, have we?. For a proper fix, we need at least 2 locations for each token that comes from an expansion. The place where the token really appeared and the place where it ended up. However, this is not trivial. We need either to encode such information in 1 location_t number somehow or to encode it in the token. 4.3.2 is released, changing milestones to 4.3.3. 2 locations won't help you either.
void foo ()
{
#define EMPTY
while (0)EMPTY;
}
won't warn when compiled with g++ -Wempty-body -O2, but will with
g++ -Wempty-body -O2 -save-temps (i.e. ccache etc.). I think it is unfortunate
this -Wempty-body extension was accepted for 4.3, and if we want to make it work, we really have to handle it at the preprocessor level.
Patch posted. Subject: Bug 36478 Author: jakub Date: Wed Nov 12 22:18:03 2008 New Revision: 141810 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=141810 Log: PR c++/36478 Revert: 2007-05-07 Mike Stump <mrs@apple.com> * doc/invoke.texi (Warning Options): Document that -Wempty-body also checks for and while statements in C++. Revert: 2007-05-07 Mike Stump <mrs@apple.com> * parser.c (check_empty_body): Add. (cp_parser_iteration_statement): Add call to check_empty_body. * g++.old-deja/g++.mike/empty.C: Remove. Removed: trunk/gcc/testsuite/g++.old-deja/g++.mike/empty.C Modified: trunk/gcc/ChangeLog trunk/gcc/cp/ChangeLog trunk/gcc/cp/parser.c trunk/gcc/doc/invoke.texi trunk/gcc/testsuite/ChangeLog GCC 4.3.3 is being released, adjusting target milestone. GCC 4.3.4 is being released, adjusting target milestone. GCC 4.3.5 is being released, adjusting target milestone. Fixed in 4.4+ only as the -Wempty-body patch was reverted. The underlying problem can be tracked by PR7263. |