[NFC] Remove LLVM_ALIGNAS

[jfb]

Summary

The minimum compilers support all have alignas, and we don't use LLVM_ALIGNAS anywhere anymore. This also removes an MSVC diagnostic which, according to the comment above, isn't relevant anymore.

[rnk]

lgtm

clang-tools-extra/docs/doxygen.cfg.in

 # The PREDEFINED tag can be used to specify one or more macro names that are
 # defined before the preprocessor is started (similar to the -D option of e.g.
 # gcc). The argument of the tag is a list of macros of the form: name or
 # name=definition (no spaces). If the definition and the "=" are omitted, "=1"
 # is assumed. To prevent a macro definition from being undefined via #undef or
 # recursively expanded use the := operator instead of the = operator.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
-PREDEFINED             = LLVM_ALIGNAS(x)=
+PREDEFINED             =
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The
 # macro definition that is found in the sources will be used. Use the PREDEFINED
 # tag if you want to use a different macro definition that overrules the
 # definition found in the source code.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 

clang/docs/doxygen.cfg.in

 # The PREDEFINED tag can be used to specify one or more macro names that are
 # defined before the preprocessor is started (similar to the -D option of e.g.
 # gcc). The argument of the tag is a list of macros of the form: name or
 # name=definition (no spaces). If the definition and the "=" are omitted, "=1"
 # is assumed. To prevent a macro definition from being undefined via #undef or
 # recursively expanded use the := operator instead of the = operator.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
-PREDEFINED             = LLVM_ALIGNAS(x)=
+PREDEFINED             =
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The
 # macro definition that is found in the sources will be used. Use the PREDEFINED
 # tag if you want to use a different macro definition that overrules the
 # definition found in the source code.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 

llvm/cmake/modules/HandleLLVMOptions.cmake

set(msvc_warning_flags
           # Update 1. Re-evaluate the usefulness of this diagnostic with Update 2.
       -wd4592 # Suppress ''var': symbol will be dynamically initialized (implementation limitation)
       -wd4319 # Suppress ''operator' : zero extending 'type' to 'type' of greater size'
           # C4709 is disabled because of a bug with Visual Studio 2017 as of
           # v15.8.8. Re-evaluate the usefulness of this diagnostic when the bug
           # is fixed.
       -wd4709 # Suppress comma operator within array index expression
 
-      # Ideally, we'd like this warning to be enabled, but MSVC 2013 doesn't
-      # support the 'aligned' attribute in the way that clang sources requires (for
-      # any code that uses the LLVM_ALIGNAS macro), so this is must be disabled to
-      # avoid unwanted alignment warnings.
-      # When we switch to requiring a version of MSVC that supports the 'alignas'
-      # specifier (MSVC 2015?) this warning can be re-enabled.
-      -wd4324 # Suppress 'structure was padded due to __declspec(align())'
-
       # Promoted warnings.
       -w14062 # Promote 'enumerator in switch of enum is not handled' to level 1 warning.
 
       # Promoted warnings to errors.
       -we4238 # Promote 'nonstandard extension used : class rvalue used as lvalue' to error.
       )
   endif(NOT CLANG_CL)
 

llvm/docs/doxygen.cfg.in

 # The PREDEFINED tag can be used to specify one or more macro names that are
 # defined before the preprocessor is started (similar to the -D option of e.g.
 # gcc). The argument of the tag is a list of macros of the form: name or
 # name=definition (no spaces). If the definition and the "=" are omitted, "=1"
 # is assumed. To prevent a macro definition from being undefined via #undef or
 # recursively expanded use the := operator instead of the = operator.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
-PREDEFINED             = LLVM_ALIGNAS(x)=
+PREDEFINED             =
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The
 # macro definition that is found in the sources will be used. Use the PREDEFINED
 # tag if you want to use a different macro definition that overrules the
 # definition found in the source code.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 

llvm/include/llvm/Support/Compiler.h

 #elif defined(LLVM_BUILTIN_UNREACHABLE)
 // As of today, clang does not support __builtin_assume_aligned.
 # define LLVM_ASSUME_ALIGNED(p, a) \
            (((uintptr_t(p) % (a)) == 0) ? (p) : (LLVM_BUILTIN_UNREACHABLE, (p)))
 #else
 # define LLVM_ASSUME_ALIGNED(p, a) (p)
 #endif
 
-/// \macro LLVM_ALIGNAS
-/// Used to specify a minimum alignment for a structure or variable.
-#if __GNUC__ && !__has_feature(cxx_alignas) && !LLVM_GNUC_PREREQ(4, 8, 1)
-# define LLVM_ALIGNAS(x) __attribute__((aligned(x)))
-#else
-# define LLVM_ALIGNAS(x) alignas(x)
-#endif
-
 /// \macro LLVM_PACKED
 /// Used to specify a packed structure.
 /// LLVM_PACKED(
 ///    struct A {
 ///      int i;
 ///      int j;
 ///      int k;
 ///      long long l;

 #else
 # define LLVM_PACKED(d) d __attribute__((packed))
 # define LLVM_PACKED_START _Pragma("pack(push, 1)")
 # define LLVM_PACKED_END   _Pragma("pack(pop)")
 #endif
 
 /// \macro LLVM_PTR_SIZE
 /// A constant integer equivalent to the value of sizeof(void*).
-/// Generally used in combination with LLVM_ALIGNAS or when doing computation in
-/// the preprocessor.
+/// Generally used in combination with alignas or when doing computation in the
+/// preprocessor.
 #ifdef __SIZEOF_POINTER__
 # define LLVM_PTR_SIZE __SIZEOF_POINTER__
 #elif defined(_WIN64)
 # define LLVM_PTR_SIZE 8
 #elif defined(_WIN32)
 # define LLVM_PTR_SIZE 4
 #elif defined(_MSC_VER)
 # error "could not determine LLVM_PTR_SIZE as a constant int for MSVC"

llvm/unittests/Support/AlignOfTest.cpp

 #elif ((__GNUC__ * 100) + __GNUC_MINOR__) >= 402
 // Pragma based warning suppression was introduced in GGC 4.2.  Additionally
 // this warning is "enabled by default".  The warning still appears if -Wall is
 // suppressed.  Apparently GCC suppresses it when -w is specifed, which is odd.
 #pragma GCC diagnostic warning "-w"
 #endif
 
 // Define some fixed alignment types to use in these tests.
-struct LLVM_ALIGNAS(1) A1 {};
-struct LLVM_ALIGNAS(2) A2 {};
-struct LLVM_ALIGNAS(4) A4 {};
-struct LLVM_ALIGNAS(8) A8 {};
+struct alignas(1) A1 {};
+struct alignas(2) A2 {};
+struct alignas(4) A4 {};
+struct alignas(8) A8 {};
 
 struct S1 {};
 struct S2 { char a; };
 struct S3 { int x; };
 struct S4 { double y; };
 struct S5 { A1 a1; A2 a2; A4 a4; A8 a8; };
 struct S6 { double f(); };
 struct D1 : S1 {};