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[libc++][AIX] Make basic_string layout compatible with earlier version

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Summary:
Patch D123580 changed to use bit fields for strings in long and short mode. As a result, this changes the layout of these strings on AIX because bit fields on AIX are 4 bytes, which breaks the ABI compatibility with earlier strings before the change on AIX. This patch uses the attribute 'packed' and anonymous structure to make string layout compatible. This patch will also make test cases alignof.compile.pass.cpp and sizeof.compile.pass.cpp introduced in D127672 pass on AIX.

Reviewed by: philnik, Mordante, hubert.reinterpretcast, libc++

Differential Revision: https://reviews.llvm.org/D128285
This commit is contained in:
Xing Xue
2022-06-24 17:25:15 -04:00
parent 00e9d53453
commit 60f7bdfd03
2 changed files with 18 additions and 4 deletions
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16
libcxx/include/string
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@@ -721,10 +721,16 @@ private:
static const size_type __endian_factor = 2;
#endif
// Attribute 'packed' is used to keep the layout compatible with the
// previous definition that did not use bit fields. This is because on
// some platforms bit fields have a default size rather than the actual
// size used, e.g., it is 4 bytes on AIX. See D128285 for details.
struct __long
{
size_type __is_long_ : 1;
size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
struct _LIBCPP_PACKED {
size_type __is_long_ : 1;
size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
};
size_type __size_;
pointer __data_;
};
@@ -734,8 +740,10 @@ private:
struct __short
{
unsigned char __is_long_ : 1;
unsigned char __size_ : 7;
struct _LIBCPP_PACKED {
unsigned char __is_long_ : 1;
unsigned char __size_ : 7;
};
char __padding_[sizeof(value_type) - 1];
value_type __data_[__min_cap];
};