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Re: CC register for x86-64 asm statements. Was: glibc: syscalls for x86-64
- To: aj at suse dot de, rth at redhat dot com
- Subject: Re: CC register for x86-64 asm statements. Was: glibc: syscalls for x86-64
- From: dewar at gnat dot com (Robert Dewar)
- Date: Wed, 22 Nov 2000 21:14:34 -0500 (EST)
- Cc: discuss at x86-64 dot org, gcc at gcc dot gnu dot org, jh at suse dot cz
<<I agree. There are few enough instructions that don't
clobber flags that there is often little benefit.
>>
There are actually many uses of retaining flags over instructions that
do not affect them, although few compilers really take advantage of this
(an interesting bit of history here is that the first IBM portable
computer -- the convertible -- was based on the Harris 80C88. This machine
had a bug that caused CVD to clobber flags. The only known piece of software
affected was the Realia COBOL compiler -- IBM asked us to change the
compiler :-)