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author | Akira Hatanaka <ahatanaka@apple.com> | 2018-07-20 17:10:32 +0000 |
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committer | Akira Hatanaka <ahatanaka@apple.com> | 2018-07-20 17:10:32 +0000 |
commit | dbfa453e4138bb977644929c69d1c71e5e8b4bee (patch) | |
tree | fd0755e09eefe0ed813945492b2886441d6e8334 /clang/docs/Block-ABI-Apple.rst | |
parent | c358e51e9b9d42be542ae577d10b851e9358cd39 (diff) | |
download | llvm-dbfa453e4138bb977644929c69d1c71e5e8b4bee.zip llvm-dbfa453e4138bb977644929c69d1c71e5e8b4bee.tar.gz llvm-dbfa453e4138bb977644929c69d1c71e5e8b4bee.tar.bz2 |
[CodeGen][ObjC] Make copying and disposing of a non-escaping block
no-ops.
A non-escaping block on the stack will never be called after its
lifetime ends, so it doesn't have to be copied to the heap. To prevent
a non-escaping block from being copied to the heap, this patch sets
field 'isa' of the block object to NSConcreteGlobalBlock and sets the
BLOCK_IS_GLOBAL bit of field 'flags', which causes the runtime to treat
the block as if it were a global block (calling _Block_copy on the block
just returns the original block and calling _Block_release is a no-op).
Also, a new flag bit 'BLOCK_IS_NOESCAPE' is added, which allows the
runtime or tools to distinguish between true global blocks and
non-escaping blocks.
rdar://problem/39352313
Differential Revision: https://reviews.llvm.org/D49303
llvm-svn: 337580
Diffstat (limited to 'clang/docs/Block-ABI-Apple.rst')
-rw-r--r-- | clang/docs/Block-ABI-Apple.rst | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/clang/docs/Block-ABI-Apple.rst b/clang/docs/Block-ABI-Apple.rst index 7f49bbd..e48a24b 100644 --- a/clang/docs/Block-ABI-Apple.rst +++ b/clang/docs/Block-ABI-Apple.rst @@ -61,6 +61,14 @@ The following flags bits are in use thusly for a possible ABI.2010.3.16: .. code-block:: c enum { + // Set to true on blocks that have captures (and thus are not true + // global blocks) but are known not to escape for various other + // reasons. For backward compatiblity with old runtimes, whenever + // BLOCK_IS_NOESCAPE is set, BLOCK_IS_GLOBAL is set too. Copying a + // non-escaping block returns the original block and releasing such a + // block is a no-op, which is exactly how global blocks are handled. + BLOCK_IS_NOESCAPE = (1 << 23), + BLOCK_HAS_COPY_DISPOSE = (1 << 25), BLOCK_HAS_CTOR = (1 << 26), // helpers have C++ code BLOCK_IS_GLOBAL = (1 << 28), |