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Il 16/12/2013 01:30, Matt Turner ha scritto: |
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> On Sun, Dec 15, 2013 at 4:20 PM, Andreas K. Huettel |
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> <dilfridge@g.o> wrote: |
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>> Am Montag, 16. Dezember 2013, 00:34:13 schrieb Matt Turner: |
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>>> 3dnow: Use the 3DNow! instruction set |
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>>> 3dnowext: Use the Enhanced 3DNow! instruction set |
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>>> mmx: Use the MMX instruction set |
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>>> mmxext: Use the Extended MMX instruction set (intersection of Enhanced |
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>>> 3DNow! and SSE instruction sets) (3dnowext or sse in cpuinfo) |
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>>> sse: Use the SSE instruction set |
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>>> sse2: Use the SSE2 instruction set |
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>>> sse3: Use the SSE3 instruction set (pni in cpuinfo) |
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>>> ssse3: Use the SSSE3 instruction set |
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>>> sse4_1: Use the SSE 4.1 instruction set |
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>>> avx: Use the AVX instruction set |
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>>> avx2: Use the AVX2 instruction set |
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>> What's the point of these flags? |
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>> (or to be more precise, are they really justified whenever they are used?) |
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>> |
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>> Usually the set of cpu instructions should be controlled by your CFLAGS, and |
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>> I've been actively patching packages (that do not do manually coded assembly) |
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>> to make such flags unnecessary. |
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> Often they're for enabling assembly code that uses these instruction |
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> sets. For pixman, a package that I'm very familiar with, they turn on |
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> code using these instruction sets using intrinsics in C. I believe |
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> they are justified. |
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> |
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> If the package simply uses the flag to add an -m<isa> flag to CFLAGS, |
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> then we should definitely remove it. If I recall correctly, I have |
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> only seen one instance of this. |
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> |
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another possible case are packages that do run-time checking of usable |
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instruction set. |
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The use flag could restrict the code to be compiled and installed from |
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the ebuild. |
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Probably never used like this tough |