From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Matthias Urlichs" To: David Edelsohn Cc: Joe Buck , rth@cygnus.com, rearnsha@arm.com, mrs@wrs.com, law@cygnus.com, drepper@cygnus.com, egcs@cygnus.com, richard.earnshaw@arm.com Subject: Re: mutex in frame code Date: Sun, 28 Feb 1999 22:53:00 -0000 Message-ID: <19990202080023.B15962@noris.de> References: <9902011816.AA33418@marc.watson.ibm.com> X-SW-Source: 1999-02n/msg00071.html Message-ID: <19990228225300.GPxr032Iv33yoihPwe68XwEEwQJB0I-Ut932nI8GWm0@z> Hi, David Edelsohn: > The POWER and PowerPC architecture do not describe a nested set > which is exactly what is assumed by this entire -march= discussion. You > and Richard and others are relying on the fact that -march=X is a complete > subset of -march=X+1. On POWER and PowerPC that is not the case. > But there's an instruction set X such that all Xn with n>0 are superset of that X, right? (X may not correspond to any existing piece of hardware, but that's not the point.) The real question is, though, whether there are scheduler or other differences between different PowerPC CPUs such that optimizing for any of them makes sense. (Like the difference between i586 and i686.) If there are, an -mtune=FOO option makes sense; if not, it doesn't. > architecture. Using the option -march= but specifying CPU is confusing > and incorrect. > We need options for controlling (a) which instruction set to assume, and (b) which particular CPU to optimize for. Calling (a) -march and (b) -mcpu may not be 100% optimal or intuitive, but it's there. I'd name them (a) -mbase and (b) -mtune if I felt the need to make the option tags more unambiguous. If the assumption above doesn't hold and there are incompatible sets X and Y instead, they should have different targets. -- Matthias Urlichs | noris network GmbH | smurf@noris.de | ICQ: 20193661 The quote was selected randomly. Really. | http://www.noris.de/~smurf/ -- National security is the chief cause of national insecurity.