Distinguish `__block` variables that are captured by escaping blocks

from those that aren't.

This patch changes the way __block variables that aren't captured by
escaping blocks are handled:

- Since non-escaping blocks on the stack never get copied to the heap
  (see https://reviews.llvm.org/D49303), Sema shouldn't error out when
  the type of a non-escaping __block variable doesn't have an accessible
  copy constructor.

- IRGen doesn't have to use the specialized byref structure (see
  https://clang.llvm.org/docs/Block-ABI-Apple.html#id8) for a
  non-escaping __block variable anymore. Instead IRGen can emit the
  variable as a normal variable and copy the reference to the block
  literal. Byref copy/dispose helpers aren't needed either.

This reapplies r343518 after fixing a use-after-free bug in function
Sema::ActOnBlockStmtExpr where the BlockScopeInfo was dereferenced after
it was popped and deleted.

rdar://problem/39352313

Differential Revision: https://reviews.llvm.org/D51564

llvm-svn: 343542

1 files changed, 6 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 6ea2d75b318..54289cdd6de 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1787,7 +1787,7 @@ public:
                                 llvm::Value *ptr);
 
   Address LoadBlockStruct();
-  Address GetAddrOfBlockDecl(const VarDecl *var, bool ByRef);
+  Address GetAddrOfBlockDecl(const VarDecl *var);
 
   /// BuildBlockByrefAddress - Computes the location of the
   /// data in a variable which is declared as __block.
@@ -2683,8 +2683,9 @@ public:
 
     llvm::Value *NRVOFlag;
 
-    /// True if the variable is a __block variable.
-    bool IsByRef;
+    /// True if the variable is a __block variable that is captured by an
+    /// escaping block.
+    bool IsEscapingByRef;
 
     /// True if the variable is of aggregate type and has a constant
     /// initializer.
@@ -2704,7 +2705,7 @@ public:
 
     AutoVarEmission(const VarDecl &variable)
         : Variable(&variable), Addr(Address::invalid()), NRVOFlag(nullptr),
-          IsByRef(false), IsConstantAggregate(false),
+          IsEscapingByRef(false), IsConstantAggregate(false),
           SizeForLifetimeMarkers(nullptr), AllocaAddr(Address::invalid()) {}
 
     bool wasEmittedAsGlobal() const { return !Addr.isValid(); }
@@ -2734,7 +2735,7 @@ public:
     /// Note that this does not chase the forwarding pointer for
     /// __block decls.
     Address getObjectAddress(CodeGenFunction &CGF) const {
-      if (!IsByRef) return Addr;
+      if (!IsEscapingByRef) return Addr;
 
       return CGF.emitBlockByrefAddress(Addr, Variable, /*forward*/ false);
     }