[Bug c/86196] [9 Regression] Bogus -Wrestrict on memcpy between array elements at unequal indices

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86196

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |8.1.0
           Keywords|                            |diagnostic
   Last reconfirmed|                            |2018-06-18
                 CC|                            |msebor at gcc dot gnu.org
             Blocks|                            |84774
     Ever confirmed|0                           |1
            Summary|Bogus -Wrestrict on memcpy  |[9 Regression] Bogus
                   |                            |-Wrestrict on memcpy
                   |                            |between array elements at
                   |                            |unequal indices
      Known to fail|                            |9.0

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with the simplified test case below.  The "offset [0, 8]" notation
indicates the range the offset into an array is determined to be in.  The bug
is caused by GCC incorrectly computing the offset to be between 0 and 8 bytes
(the 8 is the size of the struct).

$ cat pr86196.c && gcc -O2 -S -Wall pr86196.c
struct S { int i; void *p; };

void g (struct S *a, int i, int j)
{
  if (i != j)
    __builtin_memcpy (&a[j], &a[i], sizeof (struct S));
}

pr86196.c: In function ‘g’:
pr86196.c:6:5: warning: ‘__builtin_memcpy’ accessing 16 bytes at offsets [0, 8]
and [0, 8] overlaps between 8 and 16 bytes at offset [0, 8] [-Wrestrict]
     __builtin_memcpy (&a[j], &a[i], sizeof (struct S));
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The regression was introduced in r260280:

r260280 | msebor | 2018-05-15 22:30:38 -0400 (Tue, 15 May 2018) | 15 lines

PR tree-optimization/85753 - missing -Wrestrict on memcpy into a member array

gcc/ChangeLog:

        PR tree-optimization/85753
        * gimple-ssa-warn-restrict.c (builtin_memref::builtin_memref): Handle
        RECORD_TYPE in addition to ARRAY_TYPE.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84774
[Bug 84774] [meta-bug] bogus/missing -Wrestrict