Check if NEON extension are actually available #4154
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User may pass own compiler flags to configure which override those provided by project through automake. Therefore it is possible for user on ARM platform to pass CXXFLAGS=-mfpu=vfp which will effectively disable NEON even though used compiler supports -mfpu=neon (since user supplied flags take precedence compiler invocation will use flags: -mfpu=neon -mfpu=vfp). Instead of checking whether compiler supports -mfpu=neon flag, check if NEON extensions are available by checking if __ARM_NEON is defined when compiling with -mfpu=neon and user supplied flags combined. Signed-off-by: Jan Palus <jpalus@fastmail.com>
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Why should users want to disable NEON instructions? |
In a distribution I'm targeting ARMv6 CPU with hardware float unit Would it hurt if these two sources were compiled with NEON enabled? No since NEON is detected at runtime anyway. That's how automake works unfortunately -- last word is always given to user. The only alternative would be to construct compilation command manually but I doubt it's worth the effort. |
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Feb 29, 2024
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User may pass own compiler flags to configure which override those provided by project through automake. Therefore it is possible for user on ARM platform to pass CXXFLAGS=-mfpu=vfp which will effectively disable NEON even though used compiler supports -mfpu=neon (since user supplied flags take precedence compiler invocation will use flags: -mfpu=neon -mfpu=vfp). Instead of checking whether compiler supports -mfpu=neon flag, check if NEON extensions are available by checking if __ARM_NEON is defined when compiling with -mfpu=neon and user supplied flags combined.