[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
diff --git a/clang/lib/CodeGen/CGBlocks.cpp b/clang/lib/CodeGen/CGBlocks.cpp
index 926683d..352a02d 100644
--- a/clang/lib/CodeGen/CGBlocks.cpp
+++ b/clang/lib/CodeGen/CGBlocks.cpp
@@ -104,7 +104,7 @@
elements.addInt(ulong, blockInfo.BlockSize.getQuantity());
// Optional copy/dispose helpers.
- if (blockInfo.NeedsCopyDispose) {
+ if (blockInfo.needsCopyDisposeHelpers()) {
// copy_func_helper_decl
elements.add(buildCopyHelper(CGM, blockInfo));
@@ -159,6 +159,7 @@
/// These are the flags (with corresponding bit number) that the
/// compiler is actually supposed to know about.
+ /// 23. BLOCK_IS_NOESCAPE - indicates that the block is non-escaping
/// 25. BLOCK_HAS_COPY_DISPOSE - indicates that the block
/// descriptor provides copy and dispose helper functions
/// 26. BLOCK_HAS_CXX_OBJ - indicates that there's a captured
@@ -778,8 +779,13 @@
llvm::Constant *descriptor;
BlockFlags flags;
if (!IsOpenCL) {
- isa = llvm::ConstantExpr::getBitCast(CGM.getNSConcreteStackBlock(),
- VoidPtrTy);
+ // If the block is non-escaping, set field 'isa 'to NSConcreteGlobalBlock
+ // and set the BLOCK_IS_GLOBAL bit of field 'flags'. Copying a non-escaping
+ // block just returns the original block and releasing it is a no-op.
+ llvm::Constant *blockISA = blockInfo.getBlockDecl()->doesNotEscape()
+ ? CGM.getNSConcreteGlobalBlock()
+ : CGM.getNSConcreteStackBlock();
+ isa = llvm::ConstantExpr::getBitCast(blockISA, VoidPtrTy);
// Build the block descriptor.
descriptor = buildBlockDescriptor(CGM, blockInfo);
@@ -788,12 +794,14 @@
flags = BLOCK_HAS_SIGNATURE;
if (blockInfo.HasCapturedVariableLayout)
flags |= BLOCK_HAS_EXTENDED_LAYOUT;
- if (blockInfo.NeedsCopyDispose)
+ if (blockInfo.needsCopyDisposeHelpers())
flags |= BLOCK_HAS_COPY_DISPOSE;
if (blockInfo.HasCXXObject)
flags |= BLOCK_HAS_CXX_OBJ;
if (blockInfo.UsesStret)
flags |= BLOCK_USE_STRET;
+ if (blockInfo.getBlockDecl()->doesNotEscape())
+ flags |= BLOCK_IS_NOESCAPE | BLOCK_IS_GLOBAL;
}
auto projectField =
diff --git a/clang/lib/CodeGen/CGBlocks.h b/clang/lib/CodeGen/CGBlocks.h
index 80e255f..5a8e960 100644
--- a/clang/lib/CodeGen/CGBlocks.h
+++ b/clang/lib/CodeGen/CGBlocks.h
@@ -54,6 +54,7 @@
};
enum BlockLiteralFlags {
+ BLOCK_IS_NOESCAPE = (1 << 23),
BLOCK_HAS_COPY_DISPOSE = (1 << 25),
BLOCK_HAS_CXX_OBJ = (1 << 26),
BLOCK_IS_GLOBAL = (1 << 28),
@@ -214,7 +215,8 @@
/// no non-constant captures.
bool CanBeGlobal : 1;
- /// True if the block needs a custom copy or dispose function.
+ /// True if the block has captures that would necessitate custom copy or
+ /// dispose helper functions if the block were escaping.
bool NeedsCopyDispose : 1;
/// HasCXXObject - True if the block's custom copy/dispose functions
@@ -276,6 +278,11 @@
}
CGBlockInfo(const BlockDecl *blockDecl, StringRef Name);
+
+ // Indicates whether the block needs a custom copy or dispose function.
+ bool needsCopyDisposeHelpers() const {
+ return NeedsCopyDispose && !Block->doesNotEscape();
+ }
};
} // end namespace CodeGen