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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: Andreas Gustafsson <gson%gson.org@localhost>
gson%gson.org@localhost (Andreas Gustafsson)
Subject: Re: toolchain/50940: cc -ffast-math fails to disable denormals on
Date: Fri, 11 Mar 2016 18:07:56 +0200
Joerg Sonnenberger 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.
That may be - I haven't found any documention on what the exact
assumptions are. If you know of some, I would appreciate a pointer.
> Whether the CPU generates them or not is a secondary question -- at
> that point you are already in Undefined Behavior land for this
Do you at least agree that the current NetBSD behavior is incorrect?
Andreas Gustafsson, gson%gson.org@localhost
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