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tuklib_integer: Update the CMake test for fast unaligned access.

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This commit is contained in:
Lasse Collin 2023-10-14 20:16:13 +03:00
parent 2f81ac852b
commit 9a78971261
1 changed files with 54 additions and 15 deletions
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67
cmake/tuklib_integer.cmake
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@ -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")
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."