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, 59 insertions, 0 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index d777afe9811..ccbbe50093b 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -1401,9 +1401,68 @@ void Sema::RecordParsingTemplateParameterDepth(unsigned Depth) {
       "Remove assertion if intentionally called in a non-lambda context.");
 }
 
+// Check that the type of the VarDecl has an accessible copy constructor and
+// resolve its destructor's exception spefication.
+static void checkEscapingByref(VarDecl *VD, Sema &S) {
+  QualType T = VD->getType();
+  EnterExpressionEvaluationContext scope(
+      S, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+  SourceLocation Loc = VD->getLocation();
+  Expr *VarRef = new (S.Context) DeclRefExpr(VD, false, T, VK_LValue, Loc);
+  ExprResult Result = S.PerformMoveOrCopyInitialization(
+      InitializedEntity::InitializeBlock(Loc, T, false), VD, VD->getType(),
+      VarRef, /*AllowNRVO=*/true);
+  if (!Result.isInvalid()) {
+    Result = S.MaybeCreateExprWithCleanups(Result);
+    Expr *Init = Result.getAs<Expr>();
+    S.Context.setBlockVarCopyInit(VD, Init, S.canThrow(Init));
+  }
+
+  // The destructor's exception spefication is needed when IRGen generates
+  // block copy/destroy functions. Resolve it here.
+  if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl())
+    if (CXXDestructorDecl *DD = RD->getDestructor()) {
+      auto *FPT = DD->getType()->getAs<FunctionProtoType>();
+      S.ResolveExceptionSpec(Loc, FPT);
+    }
+}
+
+static void markEscapingByrefs(const FunctionScopeInfo &FSI, Sema &S) {
+  // Set the EscapingByref flag of __block variables captured by
+  // escaping blocks.
+  for (const BlockDecl *BD : FSI.Blocks) {
+    if (BD->doesNotEscape())
+      continue;
+    for (const BlockDecl::Capture &BC : BD->captures()) {
+      VarDecl *VD = BC.getVariable();
+      if (VD->hasAttr<BlocksAttr>())
+        VD->setEscapingByref();
+    }
+  }
+
+  for (VarDecl *VD : FSI.ByrefBlockVars) {
+    // __block variables might require us to capture a copy-initializer.
+    if (!VD->isEscapingByref())
+      continue;
+    // 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 (VD->getType()->isStructureOrClassType())
+      checkEscapingByref(VD, S);
+  }
+}
+
 void Sema::PopFunctionScopeInfo(const AnalysisBasedWarnings::Policy *WP,
                                 const Decl *D, const BlockExpr *blkExpr) {
   assert(!FunctionScopes.empty() && "mismatched push/pop!");
+
+  // This function shouldn't be called after popping the current function scope.
+  // markEscapingByrefs calls PerformMoveOrCopyInitialization, which can call
+  // PushFunctionScope, which can cause clearing out PreallocatedFunctionScope
+  // when FunctionScopes is empty.
+  markEscapingByrefs(*FunctionScopes.back(), *this);
+
   FunctionScopeInfo *Scope = FunctionScopes.pop_back_val();
 
   if (LangOpts.OpenMP)