build(CMake): Rework NEON detection

Given the myriad of `-mfpu` options for ARM [1], the inability to
portably query for CPU support, and the lack of standardized ISA names
we have no other choice, but to opt out of automatically supplying NEON
compile flags. Instead we simply add the NEON optimized source file if
we detect an ISA with guaranteed NEON support (>= ARMv8) or the user
explicitly requests it (in which case he is expected to provide the
compile flags with `CMAKE_C_FLAGS` or `BLAKE3_CFLAGS_NEON` either
through a toolchain file or commandline parameters).

[1]: https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html

1 files changed, 10 insertions, 7 deletions

diff --git a/c/CMakeLists.txt b/c/CMakeLists.txt
index 1414b5f..47706d1 100644
--- a/c/CMakeLists.txt
+++ b/c/CMakeLists.txt
@@ -24,12 +24,11 @@ elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU"
   set(BLAKE3_CFLAGS_SSE4.1 "-msse4.1" CACHE STRING "the compiler flags to enable SSE4.1")
   set(BLAKE3_CFLAGS_AVX2 "-mavx2" CACHE STRING "the compiler flags to enable AVX2")
   set(BLAKE3_CFLAGS_AVX512 "-mavx512f -mavx512vl" CACHE STRING "the compiler flags to enable AVX512")
-  set(BLAKE3_CFLAGS_NEON "-mfpu=neon" CACHE STRING "the compiler flags to enable NEON")
 endif()
 # architecture lists for which to enable assembly / SIMD sources
 set(BLAKE3_AMD64_NAMES amd64 AMD64 x86_64)
 set(BLAKE3_X86_NAMES i686 x86 X86)
-set(BLAKE3_ARM_NAMES aarch64 AArch64 arm64 ARM64 armv8 armv8a)
+set(BLAKE3_ARMv8_NAMES aarch64 AArch64 arm64 ARM64 armv8 armv8a)
 
 # library target
 add_library(blake3
@@ -122,17 +121,21 @@ elseif((CMAKE_SYSTEM_PROCESSOR IN_LIST BLAKE3_X86_NAMES OR BLAKE3_USE_X86_INTRIN
   set_source_files_properties(blake3_sse2.c PROPERTIES COMPILE_FLAGS "${BLAKE3_CFLAGS_SSE2}")
   set_source_files_properties(blake3_sse41.c PROPERTIES COMPILE_FLAGS "${BLAKE3_CFLAGS_SSE4.1}")
 
-elseif((ANDROID_ABI STREQUAL "armeabi-v7a"
-          OR CMAKE_SYSTEM_PROCESSOR IN_LIST BLAKE3_ARM_NAMES
-          OR BLAKE3_USE_NEON_INTRINSICS)
-       AND DEFINED BLAKE3_CFLAGS_NEON)
+elseif(CMAKE_SYSTEM_PROCESSOR IN_LIST BLAKE3_ARMv8_NAMES
+        OR ((ANDROID_ABI STREQUAL "armeabi-v7a"
+            OR BLAKE3_USE_NEON_INTRINSICS)
+          AND (DEFINED BLAKE3_CFLAGS_NEON
+            OR CMAKE_SIZEOF_VOID_P EQUAL 8)))
   set(BLAKE3_SIMD_NEON_INTRINSICS ON)
 
   target_sources(blake3 PRIVATE
     blake3_neon.c
   )
   set_source_files_properties(blake3_dispatch.c PROPERTIES COMPILE_DEFINITIONS BLAKE3_USE_NEON=1)
-  set_source_files_properties(blake3_neon.c PROPERTIES COMPILE_FLAGS "${BLAKE3_CFLAGS_NEON}")
+
+  if (DEFINED BLAKE3_CFLAGS_NEON)
+    set_source_files_properties(blake3_neon.c PROPERTIES COMPILE_FLAGS "${BLAKE3_CFLAGS_NEON}")
+  endif()
 
 else()
   BLAKE3_DISABLE_SIMD()