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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/113365] LONG DOUBLE: denormals: assigning a constant:
 factor 100 slow,
Date: Fri, 12 Jan 2024 23:50:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113365

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
At -O0, GCC produces a lot of load/stores to the stack and subnormals always
have a penality in HW for x87.

Note double uses SSE while long double uses x87 so the effect there will sh=
ow
up more.

Note if we use -O2 and change the variable to be a volatile variable (other=
wise
the loop is just optimized away), the speed difference is gone because you =
no
longer have addition happening of a subnormal which is what is causing the =
slow
down.


Anyways as I mentioned this is not a GCC bug but rather a HW limitation.=20

There are many other targets where subnormals are slow even for double too.=