r291477 - [Frontend] Correct values of ATOMIC_*_LOCK_FREE to match builtin

[Hans Wennborg via cfe-commits]

This was reverted in r296063 due to PR31864.

On Mon, Jan 9, 2017 at 12:54 PM, Michal Gorny via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> Author: mgorny
> Date: Mon Jan  9 14:54:20 2017
> New Revision: 291477
>
> URL: http://llvm.org/viewvc/llvm-project?rev=291477&view=rev
> Log:
> [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
>
> Modified:
>     cfe/trunk/lib/Frontend/InitPreprocessor.cpp
>     cfe/trunk/test/Sema/atomic-ops.c
>
> Modified: cfe/trunk/lib/Frontend/InitPreprocessor.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/InitPreprocessor.cpp?rev=291477&r1=291476&r2=291477&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Frontend/InitPreprocessor.cpp (original)
> +++ cfe/trunk/lib/Frontend/InitPreprocessor.cpp Mon Jan  9 14:54:20 2017
> @@ -286,12 +286,12 @@ static void DefineFastIntType(unsigned T
>
>  /// 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(c
>  #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(c
>      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
>    }
>
> Modified: cfe/trunk/test/Sema/atomic-ops.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/atomic-ops.c?rev=291477&r1=291476&r2=291477&view=diff
> ==============================================================================
> --- cfe/trunk/test/Sema/atomic-ops.c (original)
> +++ cfe/trunk/test/Sema/atomic-ops.c Mon Jan  9 14:54:20 2017
> @@ -14,11 +14,7 @@ _Static_assert(__GCC_ATOMIC_WCHAR_T_LOCK
>  _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), "");
>
>
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