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Date: Thu, 20 Aug 2015 06:20:00 -0000
From: Marc Glisse <marc.glisse@inria.fr>
Reply-To: gcc-patches@gcc.gnu.org
To: "Hurugalawadi, Naveen" <Naveen.Hurugalawadi@caviumnetworks.com>
cc: Richard Biener <richard.guenther@gmail.com>,     "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: Move some flag_unsafe_math_optimizations using simplify and match
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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.

I wonder if all the unsafe math optimizations are really ok without 
-fno-math-errno...

-- 
Marc Glisse