Date: Mon, 7 Feb 2011 13:45:31 -0500 From: David Schultz <das@freebsd.org> To: Roman Divacky <rdivacky@freebsd.org> Cc: "Pedro F. Giffuni" <giffunip@yahoo.com>, freebsd-toolchain@freebsd.org Subject: Re: -fno-math-errno by default Message-ID: <20110207184531.GA81963@zim.MIT.EDU> In-Reply-To: <20110207175454.GA52746@freebsd.org> References: <alpine.LNX.2.00.1102062007490.8943@gerinyyl> <20110207175454.GA52746@freebsd.org>
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On Mon, Feb 07, 2011, Roman Divacky wrote: > should clang follow the same and default to -fno-math-errno > on FreeBSD? > > I guess so but I want to be sure, thank you! Yes. All the flag does, at least in gcc, is inform the compiler that we don't have an old System V-style math library that sets errno instead of using floating point exception flags. The flag affects the way gcc handles built-in math functions. For instance, with -fno-math-errno, gcc is able to inline sqrt(x) into a single instruction. Without the flag, however, gcc wrongly assumes that sqrt(3) might set errno, so it generates extra code to check the sign of x and call the math library if x is negative.
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