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Re: toolchain/50940: cc -ffast-math fails to disable denormals on amd64
The following reply was made to PR toolchain/50940; it has been noted by GNATS.
From: Joerg Sonnenberger <joerg%britannica.bec.de@localhost>
Cc: toolchain-manager%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
Subject: Re: toolchain/50940: cc -ffast-math fails to disable denormals on
Date: Fri, 11 Mar 2016 16:28:38 +0100
On Fri, Mar 11, 2016 at 02:45:00PM +0000, Andreas Gustafsson wrote:
> When the -ffast-math option is enabled, gcc generates x86_64 floating
> point code that assumes that the FTZ (Flush To Zero) and DAZ
> (Denormals Are Zero) bits in the MXCSR register are set.
That's not really true. The assumption with -ffast-math is that
denormals and infinites don't happen at all. Whether the CPU generates
them or not is a secondary question -- at that point you are already in
Undefined Behavior land for this mode.
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