On Sun, Feb 21, 2010 at 9:15 AM, Geert Bosch <bo...@adacore.com> wrote:
>> As I understand it, whether -mfpmath=387 (with excess precision) or >> -mfpmath=sse is the default is also considered part of the platform API >> (like whether char is signed or unsigned by default, for example), in >> addition to the ABI issues that can slow things down when SSE is used. > > No, this is not a new ABI. The ABI stays exactly the same. The I of > ABI stands for Interface. That is, the ABI has nothing to say about > how a function will compute any results. That is the area of language > standards. The only way we'd violate the ABI is the reliance on SSE2 > instructions being available and SSE2 registers being saved by the OS. > > However, since any other compiler uses SSE2 instructions by default, > I don't see why GCC should be any different. If anything, since the > GCC target audience is more focused on Free and open source software, > we could be more aggressive in taking advantage of newer hardware. > What about an autoconf test for availability of 486 atomic instructions, > and SSE2 instructions in order, and choosing the default target based > on the host? Not too crazy, is it? > I agreed that gcc for x86 should choose a sensible default for 95% of current x86 processors in use. People with those old processors can use older gcc or -march=. Default to SSE2 is a good first step. -- H.J.
