Clang does not currently support the __ibm128 type [1] and only supports
the __ieee128 type in the unreleased 12.0.0 version [2]. That means it
is not possible to provide support for -mabi=ieeelongdouble with Clang
in an ABI compatible way (as we do for GCC by defining new facets and
other types in the __gnu_cxx_ldbl128 namespace).
By preventing the definition of _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT when
compiling with Clang, all uses of __ibm128 and __ieee128 types will be
disabled. This can be revisited in future when Clang supports the types
(and provides a way to detect that support using the preprocessor).
[1] https://reviews.llvm.org/D93377
[2] https://reviews.llvm.org/D97846
libstdc++-v3/ChangeLog:
* include/bits/c++config (_GLIBCXX_LONG_DOUBLE_ALT128_COMPAT):
Do not define when compiling with Clang.
Tested powerpc64le-linux. Committed to trunk.
commit baef0cffb58be7f5d9aeac6313ea9d8becc017b1
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Tue Mar 23 13:08:32 2021
libstdc++: Disable "ALT128" long double support for Clang
Clang does not currently support the __ibm128 type [1] and only supports
the __ieee128 type in the unreleased 12.0.0 version [2]. That means it
is not possible to provide support for -mabi=ieeelongdouble with Clang
in an ABI compatible way (as we do for GCC by defining new facets and
other types in the __gnu_cxx_ldbl128 namespace).
By preventing the definition of _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT when
compiling with Clang, all uses of __ibm128 and __ieee128 types will be
disabled. This can be revisited in future when Clang supports the types
(and provides a way to detect that support using the preprocessor).
[1] https://reviews.llvm.org/D93377
[2] https://reviews.llvm.org/D97846
libstdc++-v3/ChangeLog:
* include/bits/c++config (_GLIBCXX_LONG_DOUBLE_ALT128_COMPAT):
Do not define when compiling with Clang.
diff --git a/libstdc++-v3/include/bits/c++config
b/libstdc++-v3/include/bits/c++config
index b57ff339990..72ec91949de 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -425,9 +425,12 @@ _GLIBCXX_END_NAMESPACE_VERSION
// GLIBCXX_ABI Deprecated
// Define if compatibility should be provided for -mlong-double-64.
#undef _GLIBCXX_LONG_DOUBLE_COMPAT
+
// Define if compatibility should be provided for alternative 128-bit long
-// double formats.
+// double formats. Not possible for Clang until __ibm128 is supported.
+#ifndef __clang__
#undef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
+#endif
// Inline namespaces for long double 128 modes.
#if defined _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT \
