small tweaks to reflect statements of what really ever shipped. ABI is, and has been, accurate for what we ship.

llvm-svn: 117504

1 files changed, 5 insertions, 3 deletions

diff --git a/clang/docs/Block-ABI-Apple.txt b/clang/docs/Block-ABI-Apple.txt
index 94e75ac4577..9e2edc63d2d 100644
--- a/clang/docs/Block-ABI-Apple.txt
+++ b/clang/docs/Block-ABI-Apple.txt
@@ -67,19 +67,21 @@ enum {
     BLOCK_HAS_COPY_DISPOSE =  (1 << 25),
     BLOCK_HAS_CTOR =          (1 << 26), // helpers have C++ code
     BLOCK_IS_GLOBAL =         (1 << 28),
-    BLOCK_HAS_STRET =         (1 << 29),
+    BLOCK_HAS_STRET =         (1 << 29), // IFF BLOCK_HAS_SIGNATURE
     BLOCK_HAS_SIGNATURE =     (1 << 30), 
 };
 
-In 10.6.ABI the (1<<29) was unconditionally set and ignored by the runtime - it was a transitional marker that did not get deleted after the transition. This bit is now paired with (1<<30), and represented as the pair (3<<30), for the following combinations of valid bit settings, and their meanings.
+In 10.6.ABI the (1<<29) was usually set and was always ignored by the runtime - it had been a transitional marker that did not get deleted after the transition. This bit is now paired with (1<<30), and represented as the pair (3<<30), for the following combinations of valid bit settings, and their meanings.
 
 switch (flags & (3<<29)) {
-  case (0<<29):  <unused>    , error
+  case (0<<29):      10.6.ABI, no signature field available
   case (1<<29):      10.6.ABI, no signature field available
   case (2<<29): ABI.2010.3.16, regular calling convention, presence of signature field
   case (3<<29): ABI.2010.3.16, stret calling convention, presence of signature field,
 }
 
+The signature field is not always populated.
+
 The following discussions are presented as 10.6.ABI otherwise.
 
 Block literals may occur within functions where the structure is created in stack local memory.  They may also appear as initialization expressions for Block variables of global or static local variables.