[Sema] Diagnose default-initialization, destruction, and copying of

non-trivial C union types

This patch diagnoses uses of non-trivial C unions and structs/unions
containing non-trivial C unions in the following contexts, which require
default-initialization, destruction, or copying of the union objects,
instead of disallowing fields of non-trivial types in C unions, which is
what we currently do:

- function parameters.
- function returns.
- assignments.
- compound literals.
- block captures except capturing of `__block` variables by non-escaping
  blocks.
- local and global variable definitions.
- lvalue-to-rvalue conversions of volatile types.

See the discussion in https://reviews.llvm.org/D62988 for more background.

rdar://problem/50679094

Differential Revision: https://reviews.llvm.org/D63753

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@365985 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 3 deletions

diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 3941643893..11fed28b52 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -1658,12 +1658,24 @@ 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>())
+      if (VD->hasAttr<BlocksAttr>()) {
+        // Nothing to do if this is a __block variable captured by a
+        // non-escaping block.
+        if (BD->doesNotEscape())
+          continue;
         VD->setEscapingByref();
+      }
+      // Check whether the captured variable is or contains an object of
+      // non-trivial C union type.
+      QualType CapType = BC.getVariable()->getType();
+      if (CapType.hasNonTrivialToPrimitiveDestructCUnion() ||
+          CapType.hasNonTrivialToPrimitiveCopyCUnion())
+        S.checkNonTrivialCUnion(BC.getVariable()->getType(),
+                                BD->getCaretLocation(),
+                                Sema::NTCUC_BlockCapture,
+                                Sema::NTCUK_Destruct|Sema::NTCUK_Copy);
     }
   }