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authorLasse Collin <lasse.collin@tukaani.org>2023-10-14 20:16:13 +0300
committerLasse Collin <lasse.collin@tukaani.org>2023-10-18 19:02:45 +0300
commit9a78971261bc67622cbd7dae02f6966968ac1393 (patch)
treebbc8776ad9caba53894c309fdc3dca5206ef63fa /cmake
parentBuild: Enabled unaligned access by default on PowerPC64LE and some RISC-V. (diff)
downloadxz-9a78971261bc67622cbd7dae02f6966968ac1393.tar.xz
tuklib_integer: Update the CMake test for fast unaligned access.
Diffstat (limited to 'cmake')
-rw-r--r--cmake/tuklib_integer.cmake69
1 files changed, 54 insertions, 15 deletions
diff --git a/cmake/tuklib_integer.cmake b/cmake/tuklib_integer.cmake
index 949d2d9f..b2b2097e 100644
--- a/cmake/tuklib_integer.cmake
+++ b/cmake/tuklib_integer.cmake
@@ -59,25 +59,64 @@ function(tuklib_integer TARGET_OR_ALL)
endif()
endif()
- # Unaligned access is fast on x86(-64), big endian PowerPC, and usually on
- # 32/64-bit ARM too. There are others too and ARM could be a false match.
+ # Guess that unaligned access is fast on these archs:
+ # - 32/64-bit x86 / x86-64
+ # - 32/64-bit big endian PowerPC
+ # - 64-bit little endian PowerPC
+ # - Some 32-bit ARM
+ # - Some 64-bit ARM64 (AArch64)
+ # - Some 32/64-bit RISC-V
#
- # Guess the default value for the option.
- # CMake's ability to give info about the target arch seems bad.
- # The the same arch can have different name depending on the OS.
- #
- # FIXME: The regex is based on guessing, not on factual information!
- #
- # NOTE: Compared to the Autoconf test, this lacks the GCC/Clang test
- # on ARM and always assumes that unaligned is fast on ARM.
+ # CMake doesn't provide a standardized/normalized list of processor arch
+ # names. For example, x86-64 may be "x86_64" (Linux), "AMD64" (Windows),
+ # or even "EM64T" (64-bit WinXP).
set(FAST_UNALIGNED_GUESS OFF)
- if(CMAKE_SYSTEM_PROCESSOR MATCHES
- "[Xx3456]86|^[Xx]64|^[Aa][Mm][Dd]64|^[Aa][Rr][Mm]|^aarch|^powerpc|^ppc")
- if(NOT WORDS_BIGENDIAN OR
- NOT CMAKE_SYSTEM_PROCESSOR MATCHES "^powerpc|^ppc")
- set(FAST_UNALIGNED_GUESS ON)
+ string(TOLOWER "${CMAKE_SYSTEM_PROCESSOR}" PROCESSOR)
+
+ # There is no ^ in the first regex branch to allow "i" at the beginning
+ # so it can match "i386" to "i786", and "x86_64".
+ if(PROCESSOR MATCHES "[x34567]86|^x64|^amd64|^em64t")
+ set(FAST_UNALIGNED_GUESS ON)
+
+ elseif(PROCESSOR MATCHES "^powerpc|^ppc")
+ if(WORDS_BIGENDIAN OR PROCESSOR MATCHES "64")
+ set(FAST_UNALIGNED_GUESS ON)
+ endif()
+
+ elseif(PROCESSOR MATCHES "^arm|^aarch64|^riscv")
+ # On 32-bit and 64-bit ARM, GCC and Clang
+ # #define __ARM_FEATURE_UNALIGNED if
+ # unaligned access is supported.
+ #
+ # Exception: GCC at least up to 13.2.0
+ # defines it even when using -mstrict-align
+ # so in that case this autodetection goes wrong.
+ # Most of the time -mstrict-align isn't used so it
+ # shouldn't be a common problem in practice. See:
+ # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111555
+ #
+ # RISC-V C API Specification says that if
+ # __riscv_misaligned_fast is defined then
+ # unaligned access is known to be fast.
+ #
+ # MSVC is handled as a special case: We assume that
+ # 32/64-bit ARM supports fast unaligned access.
+ # If MSVC gets RISC-V support then this will assume
+ # fast unaligned access on RISC-V too.
+ check_c_source_compiles("
+ #if !defined(__ARM_FEATURE_UNALIGNED) \
+ && !defined(__riscv_misaligned_fast) \
+ && !defined(_MSC_VER)
+ compile error
+ #endif
+ int main(void) { return 0; }
+ "
+ TUKLIB_FAST_UNALIGNED_DEFINED_BY_PREPROCESSOR)
+ if(TUKLIB_FAST_UNALIGNED_DEFINED_BY_PREPROCESSOR)
+ set(FAST_UNALIGNED_GUESS ON)
endif()
endif()
+
option(TUKLIB_FAST_UNALIGNED_ACCESS
"Enable if the system supports *fast* unaligned memory access \
with 16-bit, 32-bit, and 64-bit integers."