On Thu, Apr 21, 2011 at 10:21 AM, Jeff Law <l...@redhat.com> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 04/07/11 18:24, Xinliang David Li wrote: >> Hi, >> >> the following patch implements the option to fine control the emitted >> warnings -- >> 1) allow suppressing warnings for use of values that may be >> uninitialized. Definitely uninitialized values that may be used >> warning is not affected >> 2) allow fine grain control on promotion of warnings to errors: >> -Wno-error=maybe-uninitialized >> >> This is useful for users who only care about definite uninitialized >> variable warnings. > I'm definitely in favor of having the ability for the user to be able to > fine tune the warnings they want. However, I have some concerns. > > First, I'm not sure how reconcile the may vs must inconsistency. We can > have an object which is used in a real statement in the IL, which we > currently would classify as must-be-uninitialized, even if the path > leading to the statement is unexecutable. I guess I want to find > better ways to describe this kind of stuff in our documentation and > switch names
There are three different kind of uninit warnings: 1) definitely uninitialized, and the use the variable dominates the exit -- this is the must be used uninitialized case 2) definitely uninitialized, but the use may not be executed at runtime; 3) Only initialized in some paths from entry to the use (the use may or may not be executed). Currently 2) and 3) uses the same warning message, which may be misleading. The proposed new option only controls 3). > > Second, I'm concerned about changing the default behaviour of > - -Wuninitialized. I don't think we ever reached a consensus on that > issue last time we tried to hash through this stuff. Maybe I missed > something, but it appears to me your patch makes -Wuninitialized only > warn about real uses and ignore uses in PHIs. No, the patch does not change the default behavior of -Wuninitialized wihch will turn on -Wmaybe-uninitialized as well. The only useful scenarios for the new option are: 1) -Wuninitialized -Wno-maybe-uninitialized 2) -Wuninitialized -Werror=uninitialized -Wno-error=maybe-uninitialized > > Given the lack of consensus (and I believe there will never be a > consensus), I believe we should keep -Wuninitialized behavior as-is and > use -Wno-maybe-uninitialized to override -Wuninitialized. Yes, that is this patch is supposed to do -- the attached test case is testing it. > > If we can come up with better switch name than -Wno-maybe-uninitialized, > that would be a good step as well. However, I'm not offhand sure what > name to use given the issues surrounding may vs must be used uninitialized. Maybe-uninitialized matches case 3) -- different from case 2 which is actually 'maybe-used-uninitialized'. Thanks, David > > jeff > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.11 (GNU/Linux) > Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ > > iQEcBAEBAgAGBQJNsGecAAoJEBRtltQi2kC7BugH/01X2ppdVUONq2fBzztxF+YR > Qn85yccwI45iizNG1dlmyZlYpATYcfTGwDkBYTjiVllhOJa64Ri6bIP3ErySPllk > OrSAbwFT96TK9/h1eGfVj45mZS3MO0Pa+sxp93noGnxIMWWOt+7LiyrfJEHHLaUK > rPhREXodzLnN0KpXTD8+RS2uzTV+YODAuiWQDkiyQ0XpjCw5w2ccc7dWnrzgvEn5 > 6x/baTqQxunV8t3/ezUlHiMcUNyMigXccFgIeRRsvMengY/reLxy7eg1i+vdeets > DyWR/Hg3HewLAQidL3SAJLLGuqTrNUZ0wswgqghqh9VllAFoUdKn0xk8GFt0wbk= > =4aA4 > -----END PGP SIGNATURE----- >
