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On Thu, 6 Jul 2006 12:52:29 +0200 |
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"Diego 'Flameeyes' Pettenò" <flameeyes@g.o> wrote: |
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> So, I've been drafting this up in my blog[1], and it is a simple way |
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> to replace the CPU feature useflags. |
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>[...] |
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To paraphrase the idea - use the compiler's knowledge of the target |
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processor to select cpu-specific code. |
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I like the idea a lot. To my mind, the sse/sse2/3dnow etc should be |
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derived from the target arch, which is what you're doing with the |
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compiler's macro definitions. This could easily be done by configure |
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scripts; perhaps it would be a good idea to look into writing some |
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autoconf macros. |
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re. hardened - all we ever need, is to be able to force a package to |
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fall back to it's portable C implementation when the asm code breaks |
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PIC (which is independent of whether it uses mmx, sse etc) or |
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generates code at runtime. I think most packages provide this, as it's |
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useful to the developer to compare the C implementation with |
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accelerated asm versions easily. |
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re. Donnie's point about non-gcc compilers - handling these can be |
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hidden in the has_cpuset() function. They can always be determined |
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from the target arch (combination of ARCH and -march or equivalent |
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CFLAGS). The suggested code already does the worst-case fall-back, as |
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it responds 'no' if the compiler doesn't support -dM or doesn't define |
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the relevant macro. |
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echo | $(tc-getCC) ${CFLAGS} -dM -E - 2>/dev/null | grep -q ${def} || |
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hasfeat="no" |
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The '2>/dev/null' is the critical element for that. |
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-- |
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Kevin F. Quinn |
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