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, 2 insertions, 31 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index f5ba87f635d..441c54dc358 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11826,37 +11826,8 @@ void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
   QualType type = var->getType();
   if (type->isDependentType()) return;
 
-  // __block variables might require us to capture a copy-initializer.
-  if (var->hasAttr<BlocksAttr>()) {
-    // It's currently invalid to ever have a __block variable with an
-    // array type; should we diagnose that here?
-
-    // Regardless, we don't want to ignore array nesting when
-    // constructing this copy.
-    if (type->isStructureOrClassType()) {
-      EnterExpressionEvaluationContext scope(
-          *this, ExpressionEvaluationContext::PotentiallyEvaluated);
-      SourceLocation poi = var->getLocation();
-      Expr *varRef =new (Context) DeclRefExpr(var, false, type, VK_LValue, poi);
-      ExprResult result
-        = PerformMoveOrCopyInitialization(
-            InitializedEntity::InitializeBlock(poi, type, false),
-            var, var->getType(), varRef, /*AllowNRVO=*/true);
-      if (!result.isInvalid()) {
-        result = MaybeCreateExprWithCleanups(result);
-        Expr *init = result.getAs<Expr>();
-        Context.setBlockVarCopyInit(var, init, canThrow(init));
-      }
-
-      // The destructor's exception spefication is needed when IRGen generates
-      // block copy/destroy functions. Resolve it here.
-      if (const CXXRecordDecl *RD = type->getAsCXXRecordDecl())
-        if (CXXDestructorDecl *DD = RD->getDestructor()) {
-          auto *FPT = DD->getType()->getAs<FunctionProtoType>();
-          FPT = ResolveExceptionSpec(poi, FPT);
-        }
-    }
-  }
+  if (var->hasAttr<BlocksAttr>())
+    getCurFunction()->addByrefBlockVar(var);
 
   Expr *Init = var->getInit();
   bool IsGlobal = GlobalStorage && !var->isStaticLocal();