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[flang] Use CMake to determine endianness.

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The preprocessor definitions __BYTE_ORDER__, __ORDER_BIG_ENDIAN__, and
__ORDER_LITTLE_ENDIAN__ are gcc extensions (also supported by clang),
but msvc (and others) do not define them. As a result __BYTE_ORDER__
and __ORDER_BIG_ENDIAN__ both evaluate to 0 by the prepreprocessor,
and __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__, the first `#if` condition
to 1, hence assuming the wrong byte order for x86(_64).

This patch instead uses CMake's TestBigEndian module to determine
target architecture's endianness at configure-time.

Note this also uses the same mechanism for the runtime. If compiling
flang as a cross-compiler, the runtime for the compile-target must be
built separately (Flang does not support the LLVM_ENABLE_RUNTIMES
mechanism yet).

Fixes llvm.org/PR51597

Reviewed By: ijan1, Leporacanthicus

Differential Revision: https://reviews.llvm.org/D109108
This commit is contained in:
Michael Kruse 2021-09-03 14:48:40 -05:00
parent 37ce7349f7
commit 84e1258feb
3 changed files with 12 additions and 4 deletions
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8
flang/CMakeLists.txt
View file

@ -295,6 +295,14 @@ if (FLANG_REPOSITORY_STRING)
add_definitions(-DFLANG_REPOSITORY_STRING="${FLANG_REPOSITORY_STRING}")
endif()
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 ()
# Configure Flang's Version.inc file.
configure_file(
${CMAKE_CURRENT_SOURCE_DIR}/include/flang/Version.inc.in

4
flang/include/flang/Evaluate/common.h
View file

@ -133,9 +133,9 @@ struct Rounding {
static constexpr Rounding defaultRounding;
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#if FLANG_BIG_ENDIAN
constexpr bool isHostLittleEndian{false};
#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#elif FLANG_LITTLE_ENDIAN
constexpr bool isHostLittleEndian{true};
#else
#error host endianness is not known

4
flang/runtime/environment.h
View file

@ -14,9 +14,9 @@
namespace Fortran::runtime {
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#if FLANG_BIG_ENDIAN
constexpr bool isHostLittleEndian{false};
#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#elif FLANG_LITTLE_ENDIAN
constexpr bool isHostLittleEndian{true};
#else
#error host endianness is not known