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On 8/2/07, Florian Philipp <f.philipp@××××××.de> wrote: |
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> Am Donnerstag 02 August 2007 23:36 schrieb Alexander Skwar: |
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> > · Florian Philipp <f.philipp@××××××.de>: |
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> > > You see, they are not compatible and even if some code works I wouldn't |
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> > > bet multimedia apps will perform well. |
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> > > |
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> > > With -mtune the instruction set stays the same. It is just "rearranged". |
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> > |
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> > Hm. Allright. When using just -mtune (ie. without -march), the |
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> > docs at |
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> > http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/i386-and-x86_002d64-Options.htm |
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> >l |
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> > |
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> > say: |
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> > | While picking a specific cpu-type will schedule things appropriately |
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> > | for that particular chip, the compiler will not generate any code that |
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> > | does not run on the i386 without the -march=cpu-type option being used. |
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> > |
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> > If -mtune=athlon-xp is used, code is generated which may make |
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> > use of 3dNOW!. 3dNOW! is, of course, not to be found on 386 :) |
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> > If the instruction set stays the same, code generated with |
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> > -mtune=athlon-xp would not be executable on 386 machines, if |
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> > I understand you correctly. |
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> > |
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> > Hm. With -mtune, the set of available instructions (ie. |
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> > stuff like 3dNOW!, I suppose?) is NOT changed from the default |
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> > of i386, is it? Or what does "Tune to cpu-type everything applicable |
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> > about the generated code, except for the ABI and the set of available |
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> > instructions." mean - especially note the "except for [...] the set of |
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> > available instructions" part. |
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> > |
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> > So with "-mtune=pentium-m -march=athlon-xp" I'm making the compiler |
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> > generate code which is "ordered" the way it's best for pentium-m |
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> > machines while allowing it to use athlon-xp instruction set? Is |
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> > that what I'm doing? |
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> > |
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> > If so, then it seems you're right - code will run, but maybe not |
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> > so well. |
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> > |
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> > Is that understanding correct? If so, then I really should think |
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> > twice about using "-mtune=pentium-m -march=athlon-xp", shouldn't |
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> > I? |
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> > |
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> > Curious, |
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> > |
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> > Alexander Skwar |
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> > -- |
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> |
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> At least that's how I understand the issue. At the moment I've got two ideas |
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> to solve your problem: |
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> |
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> 1. set march to an inferior target (pentium-3 and pentium-3m seem okay: mmx |
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> and sse) and mtune for one (or even both?) of them |
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> 2. set march to one of them and disable incompatible instruction sets with |
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> options like -mno-sse2 or -mno-3dnow |
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> |
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> |
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|
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Isn't the -march=i686 valid? |
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I guess that would be the most "compatible" option for binaries that |
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will run on AMD and Intel processors... Or simply use no "-march" |
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setting, only "-mtune"... I did that recently to switch a whole system |
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from an Athlon XP to a Intel Core Duo... |
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|
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-- |
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Daniel da Veiga |
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Computer Operator - RS - Brazil |
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