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[Flang] Detect endianness in the preprocessor (#132767)

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Summary:
Currently we use `TestBigEndian` in CMake to determine endianness. This
doesn't work on all platforms and is deprecated since CMake 3.20.
Instead of using CMake, we can just use the GNU/Clang preprocessor
definitions.

The only difficulty is MSVC, mostly because they don't support the same
macros. But, as far as I'm aware, MSVC / Windows targets are always
little endian, and if not we can just override it for that specific
target in the future.
This commit is contained in:
Joseph Huber 2025-03-24 18:29:05 -05:00 committed by GitHub
parent c221d64206
commit ef2735d243
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GPG Key ID: B5690EEEBB952194
3 changed files with 31 additions and 27 deletions
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40
flang/cmake/modules/FlangCommon.cmake
View File

@ -24,30 +24,16 @@ if (FLANG_RUNTIME_F128_MATH_LIB)
add_compile_definitions(FLANG_RUNTIME_F128_MATH_LIB="${FLANG_RUNTIME_F128_MATH_LIB}")
endif()
# The NVPTX target can't emit a binary due to the PTXAS dependency, just
# hard-code this.
if ("${LLVM_RUNTIMES_TARGET}" MATCHES "^nvptx")
add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
else ()
# Check if 128-bit float computations can be done via long double
# Note that '-nostdinc++' might be implied when this code kicks in
# (see 'runtimes/CMakeLists.txt'), so we cannot use 'cfloat' C++ header
# file in the test below.
# Compile it as C.
check_c_source_compiles(
"#include <float.h>
#if LDBL_MANT_DIG != 113
#error LDBL_MANT_DIG != 113
#endif
int main() { return 0; }
"
HAVE_LDBL_MANT_DIG_113)
include(TestBigEndian)
test_big_endian(IS_BIGENDIAN)
if (IS_BIGENDIAN)
add_compile_definitions(FLANG_BIG_ENDIAN=1)
else ()
add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
endif ()
endif ()
# Check if 128-bit float computations can be done via long double
# Note that '-nostdinc++' might be implied when this code kicks in
# (see 'runtimes/CMakeLists.txt'), so we cannot use 'cfloat' C++ header
# file in the test below.
# Compile it as C.
check_c_source_compiles(
"#include <float.h>
#if LDBL_MANT_DIG != 113
#error LDBL_MANT_DIG != 113
#endif
int main() { return 0; }
"
HAVE_LDBL_MANT_DIG_113)

17
flang/include/flang/Common/api-attrs.h
View File

@ -189,4 +189,21 @@
#define RT_OPTNONE_ATTR
#endif
/* Detect system endianness if it was not explicitly set. */
#if !defined(FLANG_LITTLE_ENDIAN) && !defined(FLANG_BIG_ENDIAN)
/* We always assume Windows is little endian, otherwise use the GCC compatible
* flags. */
#if defined(_MSC_VER) || defined(_WIN32)
#define FLANG_LITTLE_ENDIAN 1
#elif defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
#define FLANG_LITTLE_ENDIAN 1
#elif defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
#define FLANG_BIG_ENDIAN 1
#else
#error "Unknown or unsupported endianness."
#endif
#endif /* !defined(FLANG_LITTLE_ENDIAN) && !defined(FLANG_BIG_ENDIAN) */
#endif /* !FORTRAN_RUNTIME_API_ATTRS_H_ */

1
flang/include/flang/Evaluate/common.h
View File

@ -9,6 +9,7 @@
#ifndef FORTRAN_EVALUATE_COMMON_H_
#define FORTRAN_EVALUATE_COMMON_H_
#include "flang/Common/api-attrs.h"
#include "flang/Common/enum-set.h"
#include "flang/Common/idioms.h"
#include "flang/Common/indirection.h"