Am Donnerstag 02 August 2007 23:36 schrieb Alexander Skwar: > ยท Florian Philipp <[EMAIL PROTECTED]>: > > You see, they are not compatible and even if some code works I wouldn't > > bet multimedia apps will perform well. > > > > With -mtune the instruction set stays the same. It is just "rearranged". > > Hm. Allright. When using just -mtune (ie. without -march), the > docs at > http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/i386-and-x86_002d64-Options.htm >l > > say: > | While picking a specific cpu-type will schedule things appropriately > | for that particular chip, the compiler will not generate any code that > | does not run on the i386 without the -march=cpu-type option being used. > > If -mtune=athlon-xp is used, code is generated which may make > use of 3dNOW!. 3dNOW! is, of course, not to be found on 386 :) > If the instruction set stays the same, code generated with > -mtune=athlon-xp would not be executable on 386 machines, if > I understand you correctly. > > Hm. With -mtune, the set of available instructions (ie. > stuff like 3dNOW!, I suppose?) is NOT changed from the default > of i386, is it? Or what does "Tune to cpu-type everything applicable > about the generated code, except for the ABI and the set of available > instructions." mean - especially note the "except for [...] the set of > available instructions" part. > > So with "-mtune=pentium-m -march=athlon-xp" I'm making the compiler > generate code which is "ordered" the way it's best for pentium-m > machines while allowing it to use athlon-xp instruction set? Is > that what I'm doing? > > If so, then it seems you're right - code will run, but maybe not > so well. > > Is that understanding correct? If so, then I really should think > twice about using "-mtune=pentium-m -march=athlon-xp", shouldn't > I? > > Curious, > > Alexander Skwar > --
At least that's how I understand the issue. At the moment I've got two ideas to solve your problem: 1. set march to an inferior target (pentium-3 and pentium-3m seem okay: mmx and sse) and mtune for one (or even both?) of them 2. set march to one of them and disable incompatible instruction sets with options like -mno-sse2 or -mno-3dnow
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