[Bug tree-optimization/92039] [10 Regression] Spurious -Warray-bounds warnings building 32-bit glibc

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92039

--- Comment #5 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 23 Oct 2019, marxin at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92039
> 
> Martin Liška <marxin at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>            Keywords|needs-reduction             |
>                  CC|                            |marxin at gcc dot gnu.org
> 
> --- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
> Just for the record a reduced test-case:
> 
> int a[3];
> 
> void fn1(long b) {
>   int i;
>   for (i = 3; i >= b; --i)
>     a[i] = a[i - b];
> }
> 
> where does not need -m32:
> 
> $ gcc -Werror=array-bounds -O2 -c ice.i
> ice.i: In function ‘fn1’:
> ice.i:6:6: error: array subscript 3 is above array bounds of ‘int[3]’
> [-Werror=array-bounds]
>     6 |     a[i] = a[i - b];
>       |     ~^~~
> ice.i:1:5: note: while referencing ‘a’
>     1 | int a[3];
>       |     ^
> cc1: some warnings being treated as errors
> 
> $ gcc-9 -Werror=array-bounds -O2 -c ice.i

The testcase is probably misreduced since the very first iteration
will write to a[3] out of bounds so it only is valid if the loop
is not entered, thus if b < 3.