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The current architecture detection, based on the "host_cpu" part of the tuple does not work properly for a number of reason: - The code assumes that if host_cpu starts with "arm" then ARM instructions are available, which is incorrect. Indeed, Cortex-M platforms can run Linux, they are ARM platforms (so host_cpu = arm), but they don't support ARM instructions: they support only the Thumb-2 instruction set. - The armv7 case is also not very useful, as it is not standard at all to pass armv7 as host_cpu even if the host system is actually ARMv7 based. - For the same reason, the armv8 case is not very useful: ARMv8 is AArch64, and there is already a separate case to handle this architecture. So, this commit moves away from a host_cpu based logic, and instead tests using AC_CHECK_DECLS() the built-in definitions of the compiler: - If we have __ARM_ARCH_ISA_ARM defined, then it's an ARM processor that supports the ARM instruction set (this allows to exclude Thumb-2 only processors). - If we have __ARM_ARCH_7A__, then we have an ARMv7-A processor, and we can enable the corresponding optimizations - Same for __aarch64__, __i386__ and __x86_64__. In addition, we remove the AC_MSG_ERROR() that makes the build fail for all architectures but the ones that are explicitly supported. Indeed, webrtc-audio-processing builds just fine for other architectures (tested on MIPS), it's just that none of the architecture-specific optimizations will be used. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
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