On Thu, 20 Aug 2015, Richard Biener wrote:
On Thu, Aug 20, 2015 at 7:38 AM, Marc Glisse <marc.gli...@inria.fr> wrote:
On Thu, 20 Aug 2015, Hurugalawadi, Naveen wrote:
The following testcase does not generate "x" as needed.
====================
double t (double x)
{
x = sqrt (x) * sqrt (x);
return x;
}
====================
With -fno-math-errno, we CSE the calls to sqrt, so I would expect this to
match:
(mult (SQRT@1 @0) @1)
Without the flag, I expect that one will apply
(simplify
(mult (SQRT:s @0) (SQRT:s @1))
(SQRT (mult @0 @1)))
and then maybe we have something converting sqrt(x*x) to abs(x) or maybe
not.
ICK. I'd rather have CSE still CSE the two calls by adding some tricks
regarding to errno ...
I wonder if all the unsafe math optimizations are really ok without
-fno-math-errno...
Well, on GIMPLE they will preserve the original calls because of their
side-effects setting errno... on GENERIC probably not.
But we are also introducing new math calls, and I am afraid those might
set errno at an unexpected place in the code...
I don't know if anyone interested in errno would ever use
-funsafe-math-optimizations though.
--
Marc Glisse
