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[Frontend] Correct values of ATOMIC_*_LOCK_FREE to match builtin 

Correct the logic used to set ATOMIC_*_LOCK_FREE preprocessor macros not
to rely on the ABI alignment of types. Instead, just assume all those
types are aligned correctly by default since clang uses safe alignment
for _Atomic types even if the underlying types are aligned to a lower
boundary by default.

For example, the 'long long' and 'double' types on x86 are aligned to
32-bit boundary by default. However, '_Atomic long long' and '_Atomic
double' are aligned to 64-bit boundary, therefore satisfying
the requirements of lock-free atomic operations.

This fixes PR #19355 by correcting the value of
__GCC_ATOMIC_LLONG_LOCK_FREE on x86, and therefore also fixing
the assumption made in libc++ tests. This also fixes PR #30581 by
applying a consistent logic between the functions used to implement
both interfaces.

Differential Revision: https://reviews.llvm.org/D28213

llvm-svn: 291477
This commit is contained in:
Michal Gorny 2017-01-09 20:54:20 +00:00
parent 082fa545cc
commit dc155744c8
2 changed files with 4 additions and 10 deletions
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10
clang/lib/Frontend/InitPreprocessor.cpp
View File

@ -286,12 +286,12 @@ static void DefineFastIntType(unsigned TypeWidth, bool IsSigned,
/// Get the value the ATOMIC_*_LOCK_FREE macro should have for a type with
/// the specified properties.
static const char *getLockFreeValue(unsigned TypeWidth, unsigned TypeAlign,
unsigned InlineWidth) {
static const char *getLockFreeValue(unsigned TypeWidth, unsigned InlineWidth) {
// Fully-aligned, power-of-2 sizes no larger than the inline
// width will be inlined as lock-free operations.
if (TypeWidth == TypeAlign && (TypeWidth & (TypeWidth - 1)) == 0 &&
TypeWidth <= InlineWidth)
// Note: we do not need to check alignment since _Atomic(T) is always
// appropriately-aligned in clang.
if ((TypeWidth & (TypeWidth - 1)) == 0 && TypeWidth <= InlineWidth)
return "2"; // "always lock free"
// We cannot be certain what operations the lib calls might be
// able to implement as lock-free on future processors.
@ -881,7 +881,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
#define DEFINE_LOCK_FREE_MACRO(TYPE, Type) \
Builder.defineMacro("__GCC_ATOMIC_" #TYPE "_LOCK_FREE", \
getLockFreeValue(TI.get##Type##Width(), \
TI.get##Type##Align(), \
InlineWidthBits));
DEFINE_LOCK_FREE_MACRO(BOOL, Bool);
DEFINE_LOCK_FREE_MACRO(CHAR, Char);
@ -894,7 +893,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
DEFINE_LOCK_FREE_MACRO(LLONG, LongLong);
Builder.defineMacro("__GCC_ATOMIC_POINTER_LOCK_FREE",
getLockFreeValue(TI.getPointerWidth(0),
TI.getPointerAlign(0),
InlineWidthBits));
#undef DEFINE_LOCK_FREE_MACRO
}

4
clang/test/Sema/atomic-ops.c
View File

@ -14,11 +14,7 @@ _Static_assert(__GCC_ATOMIC_WCHAR_T_LOCK_FREE == 2, "");
_Static_assert(__GCC_ATOMIC_SHORT_LOCK_FREE == 2, "");
_Static_assert(__GCC_ATOMIC_INT_LOCK_FREE == 2, "");
_Static_assert(__GCC_ATOMIC_LONG_LOCK_FREE == 2, "");
#ifdef __i386__
_Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == 1, "");
#else
_Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == 2, "");
#endif
_Static_assert(__GCC_ATOMIC_POINTER_LOCK_FREE == 2, "");
_Static_assert(__c11_atomic_is_lock_free(1), "");