[Bug target/62018] FAIL: gcc.dg/torture/ftrapv-1.c * execution test on x86_64-apple-darwin13

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62018

--- Comment #12 from rguenther at suse dot de <rguenther at suse dot de> ---
On Sun, 9 Nov 2014, fxcoudert at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62018
> 
> --- Comment #8 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> ---
> (In reply to Francois-Xavier Coudert from comment #7)
> > Richard, I am willing to debug this, but don't know where to go after the above analysis.
> 
> 
> I think it's a libgcc miscompilation somehow. Directly calling __addvsi3 as
> follows:
> 
> int __addvsi3 (int, int);
> int main (void)
> { volatile int x = __addvsi3 (__INT_MAX__, 1); }
> 
> does not abort, even though (in my understanding) it should.

It definitely does on x86_64-linux.  Are you using libgcc_s from
the system (thus darwin)?  ISTR old libgcc did the arithmetic
in a bogus way (using undefined behavior).  Quoting from GCC 4.3
sources:

Wtype
__addvSI3 (Wtype a, Wtype b)
{
  const Wtype w = a + b;
^^^

  if (b >= 0 ? w < a : w > a)
    abort ();

the addition is done in signed thus invoking undefined behavior.
A fixed variant (trunk) looks like

Wtype
__addvSI3 (Wtype a, Wtype b)
{
  const Wtype w = (UWtype) a + (UWtype) b;

  if (b >= 0 ? w < a : w > a)
    abort ();

doing the addition in unsigned arithmetic.

So I bet apple GCC 4.2 is affected as well - not sure if LLVM
provides libgcc_s on newer systems.