Preprocessor: support __BIGGEST_ALIGNMENT__ macro

For compatibility with GCC (and because it's generally helpful information
otherwise inaccessible to the preprocessor). This appears to be canonically the
alignment of max_align_t (e.g. on i386, __BIGGEST_ALIGNMENT__ is 4 even though
vector types will be given greater alignment).

Patch mostly by Mats Petersson

llvm-svn: 228367

2 files changed, 6 insertions, 2 deletions

diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index ae3ba6567b4..683c7ece260 100644
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -4672,7 +4672,7 @@ public:
     MaxAtomicInlineWidth = 128;
     MaxAtomicPromoteWidth = 128;
 
-    LongDoubleWidth = LongDoubleAlign = 128;
+    LongDoubleWidth = LongDoubleAlign = SuitableAlign = 128;
     LongDoubleFormat = &llvm::APFloat::IEEEquad;
 
     // {} in inline assembly are neon specifiers, not assembly variant
@@ -5012,7 +5012,7 @@ public:
     WCharType = SignedInt;
     UseSignedCharForObjCBool = false;
 
-    LongDoubleWidth = LongDoubleAlign = 64;
+    LongDoubleWidth = LongDoubleAlign = SuitableAlign = 64;
     LongDoubleFormat = &llvm::APFloat::IEEEdouble;
 
     TheCXXABI.set(TargetCXXABI::iOS64);
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index f4241a94ae0..896277aa545 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -710,6 +710,10 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   Builder.defineMacro("__POINTER_WIDTH__",
                       Twine((int)TI.getPointerWidth(0)));
 
+  // Define __BIGGEST_ALIGNMENT__ to be compatible with gcc.
+  Builder.defineMacro("__BIGGEST_ALIGNMENT__",
+                      Twine(TI.getSuitableAlign() / TI.getCharWidth()) );
+
   if (!LangOpts.CharIsSigned)
     Builder.defineMacro("__CHAR_UNSIGNED__");