Re: Configure checks and optimizations/crc32 tests

On 08/14/2015 07:42 PM, Andres Freund wrote:
> Going over my vpaths I noticed another problem with the test. With gcc I
> get slice-by-8 instead of the runtime variant:
>
> checking for builtin __atomic int64 atomic operations... yes
> checking for __get_cpuid... yes
> checking for __cpuid... no
> checking for _mm_crc32_u8 and _mm_crc32_u32 with CFLAGS=... no
> checking for _mm_crc32_u8 and _mm_crc32_u32 with CFLAGS=-msse4.2... no
> checking which CRC-32C implementation to use... slicing-by-8
>
> That's because I get a warning
> conftest.c:179:1: warning: old-style function definition [-Wold-style-definition]
>   main ()
>   ^
> and PGAC_SSE42_CRC32_INTRINSICS turns on ac_c_werror_flag. Now I can
> work around this by , but I don't really see why that test needs to turn on
> -Werror? Isn't the point of using a linker test that we'd get a proper
> linker failure if the functions don't exist?

Yeah, it was probably just copy-pasted from the other macros in 
c-compiler.m4 without thinking.

- Heikki