[Bug tree-optimization/83543] strlen of a local array member not optimized on some targets

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83543

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-02-20
                 CC|                            |ramana at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #4 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---

(In reply to Martin Sebor from comment #0)
> Bug 83462 reports (among others) a failure in the new
> c-c++-common/Warray-bounds-4.c test on powerpc64le.  The failure is due to a
> strlen optimization that's for some reason not working on this target (and
> on some others, including arm-none-eabi) but that works fine on
> x86_64-linux.  The test case below shows the difference in cross-compiler
> output between these three architectures.

Is this because arm-none-eabi by default is a STRICT_ALIGNMENT target ? What
happens if for instance you try this with -march=armv7-a where we allow some
limited misaligned access ? 

Ramana

> 
> $ (set -x && cat z.c && for arch in '' arm-none-eabi powerpc64le-linux; do
> /ssd/build/$arch/gcc-git/gcc/xgcc -B /ssd/build/$arch/gcc-git/gcc -O2 -S
> -Wall -fdump-tree-optimized=/dev/stdout z.c; done)
> + cat z.c
> struct S { char a[7]; };
> 
> void f (void)
> {
>   struct S s = { "12345" };
>   if (__builtin_strlen (s.a) != 5)
>     __builtin_abort ();
> }
> + for arch in ''\'''\''' arm-none-eabi powerpc64le-linux
> + /ssd/build//gcc-git/gcc/xgcc -B /ssd/build//gcc-git/gcc -O2 -S -Wall
> -fdump-tree-optimized=/dev/stdout z.c
> 
> ;; Function f (f, funcdef_no=0, decl_uid=1894, cgraph_uid=0, symbol_order=0)
> 
> f ()
> {
>   <bb 2> [local count: 1073741825]:
>   return;
> 
> }
> 
> 
> + for arch in ''\'''\''' arm-none-eabi powerpc64le-linux
> + /ssd/build/arm-none-eabi/gcc-git/gcc/xgcc -B
> /ssd/build/arm-none-eabi/gcc-git/gcc -O2 -S -Wall
> -fdump-tree-optimized=/dev/stdout z.c
> 
> ;; Function f (f, funcdef_no=0, decl_uid=4155, cgraph_uid=0, symbol_order=0)
> 
> f ()
> {
>   struct S s;
>   unsigned int _1;
> 
>   <bb 2> [local count: 1073741825]:
>   s = *.LC0;
>   _1 = __builtin_strlen (&s.a);
>   if (_1 != 5)
>     goto <bb 3>; [0.00%]
>   else
>     goto <bb 4>; [99.96%]
> 
>   <bb 3> [count: 0]:
>   __builtin_abort ();
> 
>   <bb 4> [local count: 1073312327]:
>   s ={v} {CLOBBER};
>   return;
> 
> }
> 
> 
> + for arch in ''\'''\''' arm-none-eabi powerpc64le-linux
> + /ssd/build/powerpc64le-linux/gcc-git/gcc/xgcc -B
> /ssd/build/powerpc64le-linux/gcc-git/gcc -O2 -S -Wall
> -fdump-tree-optimized=/dev/stdout z.c
> 
> ;; Function f (f, funcdef_no=0, decl_uid=2784, cgraph_uid=0, symbol_order=0)
> 
> f ()
> {
>   struct S s;
>   long unsigned int _1;
> 
>   <bb 2> [local count: 1073741825]:
>   s = *.LC0;
>   _1 = __builtin_strlen (&s.a);
>   if (_1 != 5)
>     goto <bb 3>; [0.00%]
>   else
>     goto <bb 4>; [99.96%]
> 
>   <bb 3> [count: 0]:
>   __builtin_abort ();
> 
>   <bb 4> [local count: 1073312327]:
>   s ={v} {CLOBBER};
>   return;
> 
> }