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Re: [PATCH 1/3] autoconf: prefer an unrolled loop for trivial AC_CHECK_F
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From: |
Eric Blake |
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Subject: |
Re: [PATCH 1/3] autoconf: prefer an unrolled loop for trivial AC_CHECK_FUNCS |
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Date: |
Mon, 31 Oct 2016 10:28:36 -0500 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 |
On 10/31/2016 06:39 AM, Paolo Bonzini wrote:
> An unrolled loop avoids the cost of spawning sed in AS_TR_SH and
> AS_TR_CPP. Prefer it if there is nothing in the second and third
> argument of AC_CHECK_FUNCS and the first argument is a literal.
> Modify AC_CHECK_FUNCS_ONCE to avoid the variable indirection too.
>
> * lib/autoconf/functions.m4 (AC_CHECK_FUNCS): Unroll loop if safe.
> (_AC_CHECK_FUNCS): Move basic implementation here.
> (_AC_CHECK_FUNC_ONCE): Expand AC_CHECK_FUNCS here...
> (_AC_FUNCS_EXPANSION): ... and not here, so remove.
> - [$3])dnl])
> +[m4_if([$2$3]AS_LITERAL_IF([$1], [yes], [no]), []yes,
Why []yes instead of the more typical [yes] ?
If the user has (unwisely) defined yes as a macro, your version will
compare against their expansion, instead of against the intended literal.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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