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| author | Lasse Collin <lasse.collin@tukaani.org> | 2023-09-23 23:28:48 +0300 |
|---|---|---|
| committer | Lasse Collin <lasse.collin@tukaani.org> | 2023-10-18 19:02:45 +0300 |
| commit | 2f81ac852bc5aafc91c8e2adc66b5114761703c4 (patch) | |
| tree | 66d661327a0f0ab993c120dd67c5eb70c6f24e3c /m4 | |
| parent | tuklib_integer: Revise unaligned reads and writes on strict-align archs. (diff) | |
| download | xz-2f81ac852bc5aafc91c8e2adc66b5114761703c4.tar.xz | |
Build: Enabled unaligned access by default on PowerPC64LE and some RISC-V.
PowerPC64LE wasn't tested but it seems like a safe change.
POWER8 supports unaligned access in little endian mode. Testing
on godbolt.org shows that GCC uses unaligned access by default.
The RISC-V macro __riscv_misaligned_fast is very new and not
in any stable compiler release yet.
Documentation in INSTALL was updated to match.
Documentation about an autodetection bug when using ARM64 GCC
with -mstrict-align was added to INSTALL.
CMake files weren't updated yet.
Diffstat (limited to 'm4')
| -rw-r--r-- | m4/tuklib_integer.m4 | 34 |
1 files changed, 27 insertions, 7 deletions
diff --git a/m4/tuklib_integer.m4 b/m4/tuklib_integer.m4 index ab9a4056..89a53fe1 100644 --- a/m4/tuklib_integer.m4 +++ b/m4/tuklib_integer.m4 @@ -65,22 +65,42 @@ AC_MSG_CHECKING([if unaligned memory access should be used]) AC_ARG_ENABLE([unaligned-access], AS_HELP_STRING([--enable-unaligned-access], [Enable if the system supports *fast* unaligned memory access with 16-bit, 32-bit, and 64-bit integers. By default, - this is enabled only on x86, x86_64, big endian PowerPC, - and some ARM systems.]), + this is enabled on x86, x86-64, + 32/64-bit big endian PowerPC, + 64-bit little endian PowerPC, + and some ARM, ARM64, and RISC-V systems.]), [], [enable_unaligned_access=auto]) if test "x$enable_unaligned_access" = xauto ; then - # TODO: There may be other architectures, on which unaligned access - # is OK. + # NOTE: There might be other architectures on which unaligned access + # is fast. case $host_cpu in - i?86|x86_64|powerpc|powerpc64) + i?86|x86_64|powerpc|powerpc64|powerpc64le) enable_unaligned_access=yes ;; - arm*|aarch64*) + 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. AC_COMPILE_IFELSE([AC_LANG_SOURCE([ -#ifndef __ARM_FEATURE_UNALIGNED +#if !defined(__ARM_FEATURE_UNALIGNED) \ + && !defined(__riscv_misaligned_fast) \ + && !defined(_MSC_VER) compile error #endif int main(void) { return 0; } |