[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.

Reviewed By: hfinkel, efriedma

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

3 files changed, 7 insertions, 13 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 655490ba06e5..20bfbf144a30 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -298,12 +298,12 @@ 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.
@@ -1142,7 +1142,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
 #define DEFINE_LOCK_FREE_MACRO(TYPE, Type)                                     \
   Builder.defineMacro(Prefix + #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);
@@ -1157,7 +1156,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
     DEFINE_LOCK_FREE_MACRO(LLONG, LongLong);
     Builder.defineMacro(Prefix + "POINTER_LOCK_FREE",
                         getLockFreeValue(TI.getPointerWidth(0),
-                                         TI.getPointerAlign(0),
                                          InlineWidthBits));
 #undef DEFINE_LOCK_FREE_MACRO
   };
diff --git a/clang/test/Preprocessor/init-x86.c b/clang/test/Preprocessor/init-x86.c
index 339941fcf3ee..9c4e328bdf79 100644
--- a/clang/test/Preprocessor/init-x86.c
+++ b/clang/test/Preprocessor/init-x86.c
@@ -185,9 +185,9 @@
 // I386:#define __i386__ 1
 // I386:#define i386 1
 
-// RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=i386-pc-linux-gnu -target-cpu pentium4 < /dev/null | FileCheck -match-full-lines -check-prefix I386-LINUX -check-prefix I386-LINUX-ALIGN32 %s
-// RUN: %clang_cc1 -x c++ -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=i386-pc-linux-gnu -target-cpu pentium4 < /dev/null | FileCheck -match-full-lines -check-prefix I386-LINUX -check-prefix I386-LINUX-CXX -check-prefix I386-LINUX-ALIGN32 %s
-// RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=i386-pc-linux-gnu -target-cpu pentium4 -malign-double < /dev/null | FileCheck -match-full-lines -check-prefix I386-LINUX -check-prefix I386-LINUX-ALIGN64 %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=i386-pc-linux-gnu -target-cpu i486 < /dev/null | FileCheck -match-full-lines -check-prefix I386-LINUX -check-prefix I386-LINUX-ALIGN32 %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=i386-pc-linux-gnu -target-cpu pentium4 < /dev/null | FileCheck -match-full-lines -check-prefix I386-LINUX -check-prefix I386-LINUX-ALIGN64 %s
+// RUN: %clang_cc1 -x c++ -E -dM -ffreestanding -fgnuc-version=4.2.1 -triple=i386-pc-linux-gnu -target-cpu pentium4 < /dev/null | FileCheck -match-full-lines -check-prefix I386-LINUX -check-prefix I386-LINUX-ALIGN64 -check-prefix I386-LINUX-CXX %s
 //
 // I386-LINUX-NOT:#define _LP64
 // I386-LINUX:#define __BIGGEST_ALIGNMENT__ 16
diff --git a/clang/test/Sema/atomic-ops.c b/clang/test/Sema/atomic-ops.c
index 3ad469d33743..45196ea19783 100644
--- a/clang/test/Sema/atomic-ops.c
+++ b/clang/test/Sema/atomic-ops.c
@@ -33,11 +33,7 @@ _Static_assert(__GCC_ATOMIC_INT_LOCK_FREE == 2, "");
 _Static_assert(__GCC_ATOMIC_INT_LOCK_FREE == __CLANG_ATOMIC_INT_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_LONG_LOCK_FREE == 2, "");
 _Static_assert(__GCC_ATOMIC_LONG_LOCK_FREE == __CLANG_ATOMIC_LONG_LOCK_FREE, "");
-#ifdef __i386__
-_Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == 1, "");
-#else
 _Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == 2, "");
-#endif
 _Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == __CLANG_ATOMIC_LLONG_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_POINTER_LOCK_FREE == 2, "");
 _Static_assert(__GCC_ATOMIC_POINTER_LOCK_FREE == __CLANG_ATOMIC_POINTER_LOCK_FREE, "");