[PATCH] avoid assuming strncpy arrays are nul-terminated (PR 89664)

[Martin Sebor]

On 3/19/19 8:33 AM, Jeff Law wrote:
> On 3/11/19 8:27 PM, Martin Sebor wrote:
>> The -Wstringop-truncation handling for strncpy/stpncpy neglects
>> to consider that character arrays tracked by the strlen pass
>> are not necessarily nul-terminated.  It unconditionally adds
>> one when computing the size of each sequence to account for
>> the nul.  This leads to false positive warnings when checking
>> the validity of indices/pointers computed by the built-ins.
>>
>> The attached patch corrects this by adding one for the nul
>> only when the character array is known to be nul-terminated.
>>
>> Since GCC 7 does not issue the warning this is a 8/9 regression
>> that I would like to fix in both releases.  Is the patch okay
>> for trunk/gcc-8-branch?
>>
>> Tested on x86_64-linux.
>>
>> Martin
>>
>> gcc-89644.diff
>>
>> PR tree-optimization/89644 - False-positive -Warray-bounds diagnostic on strncpy
>>
>> gcc/ChangeLog:
>>
>> 	PR tree-optimization/89644
>> 	* tree-ssa-strlen.c (handle_builtin_stxncpy): Consider unterminated
>> 	arrays in determining sequence sizes in strncpy and stpncpy.
>>
>> gcc/testsuite/ChangeLog:
>>
>> 	PR tree-optimization/89644
>> 	* gcc.dg/Wstringop-truncation-8.c: New test.
> OK for the trunk as well as the affected release branches.

I just noticed some some -Wrestrict test failures that I had missed
in the test report.  The patch wasn't quite right.  Sorry about that.
I'll fix it shortly.

Martin