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Re: PR35503 - warn for restrict pointer
- From: Martin Sebor <msebor at gmail dot com>
- To: Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>, Richard Biener <rguenther at suse dot de>
- Cc: Tom de Vries <Tom_deVries at mentor dot com>, gcc Patches <gcc-patches at gcc dot gnu dot org>, Marek Polacek <polacek at redhat dot com>, "Joseph S. Myers" <joseph at codesourcery dot com>, Jason Merrill <jason at redhat dot com>
- Date: Thu, 1 Sep 2016 09:58:22 -0600
- Subject: Re: PR35503 - warn for restrict pointer
- Authentication-results: sourceware.org; auth=none
- References: <CAAgBjMkRNk3f47mXwZ6J_MyMHQym4vo3+zXCZ1R6jjrqDkKRYA@mail.gmail.com> <fcf386ee-6e1c-fb81-d43f-7e825978e0ee@mentor.com> <CAAgBjM=yQGLhxmc155Eg2ggSys0u+z8ieZebxVcoC3h5O7dk0Q@mail.gmail.com> <181560f0-c738-cff9-9002-101686da4c14@mentor.com> <alpine.LSU.2.11.1609010842570.26629@t29.fhfr.qr> <CAAgBjMnakS3C2LX3HLrABJvN3artp-MYJZr_5VZ9Z_ULe+5cwQ@mail.gmail.com>
The attached version passes bootstrap+test on ppc64le-linux-gnu.
Given that it only looks if parameters are restrict qualified and not
how they're used inside the callee,
this can have false positives as in above test-cases.
Should the warning be put in Wextra rather than Wall (I have left it
in Wall in the patch) or only enabled with -Wrestrict ?
Awesome! I've wished for years for a warning like this!
I'm curious if you've tested other examples from 6.7.3.1 of C11
besides Example 3. Example 4 seems like something GCC should be
able to detect but I didn't get a warning with the patch.
I would expect the warning to be especially valuable with string
manipulation functions like memcpy that have undefined behavior
for overlapping regions, such as in:
char a[4];
void g (void)
{
__builtin_memcpy (a, a + 1, 3);
}
But here, too, I didn't get a warning. I understand that this
case cannot be handled for arbitrary functions whose semantics
aren't known but with standard functions for which GCC provides
intrinsics the effects are known and aliasing violations can in
common cases be detected.
Martin