[Bug tree-optimization/106931] [12/13 Regression] -Wstringop-overflow false positive -O3 -fno-tree-vectorize with loop unrolling since r12-3300-gece28da924ddda8b

["msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106931

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[12/13 Regression]          |[12/13 Regression]
                   |-Wstringop-overflow false   |-Wstringop-overflow false
                   |positive  -O3               |positive  -O3
                   |-fno-tree-vectorize since   |-fno-tree-vectorize with
                   |r12-3300-gece28da924ddda8b  |loop unrolling since
                   |                            |r12-3300-gece28da924ddda8b

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
The false positive is issued for the store to A[i_90] in BB 10 by the strlen
pass, where i_90's range is [8, 8].

  <bb 10> [local count: 712060]:
  _35 = (sizetype) i_90;
  _36 = B.1_83 + _35;
  _37 = *_36;
  A[i_90] = _37;    << -Wstringop-overflow
  _20 = _93 + 9;
  i_39 = (int) _20;
  goto <bb 12>; [100.00%]

Changing i's type to unsigned avoids the warning.  The IL looks very close but
i_90's range in BB 10 is VR_UNDEFINED instead.

The following is debug_ranger() output for BBs 9 and 10 in the original test
case.

=========== BB 9 ============
Imports: _93  
Exports: _8  i_90  _93  
         _8 : _93(I)  
         _86 : i_82(I)  
         _87 : i_82(I)  B.1_83(I)  _86  
         i_90 : _8  _93(I)  
i_82    [irange] int [7, 7] NONZERO 0x7
_93     [irange] unsigned int [0, 0] NONZERO 0x0
Relational : (_8 > _93)
    <bb 9> [local count: 801058]:
    _86 = (sizetype) i_82;
    _87 = B.1_83 + _86;
    _88 = *_87;
    A[i_82] = _88;
    _8 = _93 + 8;
    i_90 = (int) _8;
    if (i_90 != 8)
      goto <bb 10>; [88.89%]
    else
      goto <bb 12>; [11.11%]

_8 : [irange] unsigned int [8, 8] NONZERO 0x8
_86 : [irange] sizetype [7, 7] NONZERO 0x7
_87 : [irange] char * [1, +INF]
i_90 : [irange] int [8, 8] NONZERO 0x8
9->10  (T) _8 :         [irange] UNDEFINED
9->10  (T) i_90 :       [irange] UNDEFINED
9->10  (T) _93 :        [irange] UNDEFINED
9->12  (F) _8 :         [irange] unsigned int [8, 8] NONZERO 0x8
9->12  (F) i_90 :       [irange] int [8, 8] NONZERO 0x8
9->12  (F) _93 :        [irange] unsigned int [0, 0] NONZERO 0x0

=========== BB 10 ============
_93     [irange] UNDEFINED
    <bb 10> [local count: 712060]:
    _35 = (sizetype) i_90;
    _36 = B.1_83 + _35;
    _37 = *_36;
    A[i_90] = _37;
    _20 = _93 + 9;
    i_39 = (int) _20;
    goto <bb 12>; [100.00%]

whereas for the unsigned case:

=========== BB 10 ============
_85     [irange] UNDEFINED
i_90    [irange] UNDEFINED