Update third_party/base/compiler_specific.h.

Import Chromium's base/compiler_specific.h from r537069.

Now that FALLTHROUGH is available via compiler_specific.h, remove
FX_FALLTHROUGH.

Change-Id: I8b9631a4f007673e10e0c26951dfd61e9dcada30
Reviewed-on: https://pdfium-review.googlesource.com/32639
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

1 files changed, 27 insertions, 29 deletions

diff --git a/third_party/base/compiler_specific.h b/third_party/base/compiler_specific.h
index 3dbd1abb33..57f7a93e59 100644
--- a/third_party/base/compiler_specific.h
+++ b/third_party/base/compiler_specific.h
@@ -43,22 +43,6 @@
 #define MSVC_DISABLE_OPTIMIZE() __pragma(optimize("", off))
 #define MSVC_ENABLE_OPTIMIZE() __pragma(optimize("", on))
 
-// Allows exporting a class that inherits from a non-exported base class.
-// This uses suppress instead of push/pop because the delimiter after the
-// declaration (either "," or "{") has to be placed before the pop macro.
-//
-// Example usage:
-// class EXPORT_API Foo : NON_EXPORTED_BASE(public Bar) {
-//
-// MSVC Compiler warning C4275:
-// non dll-interface class 'Bar' used as base for dll-interface class 'Foo'.
-// Note that this is intended to be used only when no access to the base class'
-// static data is done through derived classes or inline methods. For more info,
-// see http://msdn.microsoft.com/en-us/library/3tdb471s(VS.80).aspx
-#define NON_EXPORTED_BASE(code) \
-  MSVC_SUPPRESS_WARNING(4275)   \
-  code
-
 #else  // Not MSVC
 
 #define _Printf_format_string_
@@ -68,7 +52,6 @@
 #define MSVC_POP_WARNING()
 #define MSVC_DISABLE_OPTIMIZE()
 #define MSVC_ENABLE_OPTIMIZE()
-#define NON_EXPORTED_BASE(code) code
 
 #endif  // COMPILER_MSVC
 
@@ -78,7 +61,7 @@
 // Use like:
 //   int x = ...;
 //   ALLOW_UNUSED_LOCAL(x);
-#define ALLOW_UNUSED_LOCAL(x) false ? (void)x : (void)0
+#define ALLOW_UNUSED_LOCAL(x) (void)x
 
 // Annotate a typedef or function indicating it's ok if it's not used.
 // Use like:
@@ -112,21 +95,29 @@
 // Use like:
 //   class ALIGNAS(16) MyClass { ... }
 //   ALIGNAS(16) int array[4];
+//
+// In most places you can use the C++11 keyword "alignas", which is preferred.
+//
+// But compilers have trouble mixing __attribute__((...)) syntax with
+// alignas(...) syntax.
+//
+// Doesn't work in clang or gcc:
+//   struct alignas(16) __attribute__((packed)) S { char c; };
+// Works in clang but not gcc:
+//   struct __attribute__((packed)) alignas(16) S2 { char c; };
+// Works in clang and gcc:
+//   struct alignas(16) S3 { char c; } __attribute__((packed));
+//
+// There are also some attributes that must be specified *before* a class
+// definition: visibility (used for exporting functions/classes) is one of
+// these attributes. This means that it is not possible to use alignas() with a
+// class that is marked as exported.
 #if defined(COMPILER_MSVC)
 #define ALIGNAS(byte_alignment) __declspec(align(byte_alignment))
 #elif defined(COMPILER_GCC)
 #define ALIGNAS(byte_alignment) __attribute__((aligned(byte_alignment)))
 #endif
 
-// Return the byte alignment of the given type (available at compile time).
-// Use like:
-//   ALIGNOF(int32_t)  // this would be 4
-#if defined(COMPILER_MSVC)
-#define ALIGNOF(type) __alignof(type)
-#elif defined(COMPILER_GCC)
-#define ALIGNOF(type) __alignof__(type)
-#endif
-
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() WARN_UNUSED_RESULT;
@@ -207,7 +198,7 @@
 
 // Macro for hinting that an expression is likely to be false.
 #if !defined(UNLIKELY)
-#if defined(COMPILER_GCC)
+#if defined(COMPILER_GCC) || defined(__clang__)
 #define UNLIKELY(x) __builtin_expect(!!(x), 0)
 #else
 #define UNLIKELY(x) (x)
@@ -215,7 +206,7 @@
 #endif  // !defined(UNLIKELY)
 
 #if !defined(LIKELY)
-#if defined(COMPILER_GCC)
+#if defined(COMPILER_GCC) || defined(__clang__)
 #define LIKELY(x) __builtin_expect(!!(x), 1)
 #else
 #define LIKELY(x) (x)
@@ -230,4 +221,11 @@
 #define HAS_FEATURE(FEATURE) 0
 #endif
 
+// Macro for telling -Wimplicit-fallthrough that a fallthrough is intentional.
+#if defined(__clang__)
+#define FALLTHROUGH [[clang::fallthrough]]
+#else
+#define FALLTHROUGH
+#endif
+
 #endif  // BASE_COMPILER_SPECIFIC_H_