[multiprecision-builtins] Added missing builtin __builtin_{add,sub}cb for {add,sub} with carry for bytes.

I have had several people ask me about why this builtin was not available in
clang (since it seems like a logical conclusion). This patch implements said
builtins.

Relevant tests are included as well. I also updated the Clang language extension reference.

rdar://14192664.

llvm-svn: 184227

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index d7e88dfda9a..af9b61a704e 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -1555,10 +1555,12 @@ The complete list of builtins are:
 
 .. code-block:: c
 
+  unsigned char      __builtin_addcb (unsigned char x, unsigned char y, unsigned char carryin, unsigned char *carryout);
   unsigned short     __builtin_addcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout);
   unsigned           __builtin_addc  (unsigned x, unsigned y, unsigned carryin, unsigned *carryout);
   unsigned long      __builtin_addcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout);
   unsigned long long __builtin_addcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout);
+  unsigned char      __builtin_subcb (unsigned char x, unsigned char y, unsigned char carryin, unsigned char *carryout);
   unsigned short     __builtin_subcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout);
   unsigned           __builtin_subc  (unsigned x, unsigned y, unsigned carryin, unsigned *carryout);
   unsigned long      __builtin_subcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout);