[clang] [clang] Fix self-capturing `__block` variables (PR #89475)

[via cfe-commits]

================
@@ -2653,11 +2655,39 @@ const BlockByrefInfo &CodeGenFunction::getBlockByrefInfo(const VarDecl *D) {
   info.FieldOffset = varOffset;
   info.ByrefAlignment = std::max(varAlign, getPointerAlign());
 
+  // If we're initializing directly on the heap, then we should emit a
+  // no-op copy helper, both because we don't need a real one (the
+  // object will never move), and because a real one would break the
+  // pre-init _Block_object_assign.
+  info.ForceNoopCopy = D->needsInitOnHeap();
+
   auto pair = BlockByrefInfos.insert({D, info});
   assert(pair.second && "info was inserted recursively?");
   return pair.first->second;
 }
 
+void CodeGenFunction::emitByrefInitOnHeap(llvm::Value *P) {
+  // The object itself is initialized directly on the heap.  But for ABI
+  // backwards compatibility reasons, we have to set up a fake byref struct on
+  // the stack (with the structural components initialized but not the object
+  // itself), then call _Block_object_assign to move it to the heap (which is
+  // safe because we forced a no-op copy helper), then call
+  // _Block_object_dispose to release the extra ref from _Block_object_assign.
+  //
+  // 'P' points to the fake byref struct.
+
+  BlockFieldFlags flags = BLOCK_FIELD_IS_BYREF;
+  // Ignored out-parameter.  We'll use the forwarding pointer instead.
+  RawAddress out = CreateDefaultAlignTempAlloca(P->getType(), "initOnHeap.out");
+
+  llvm::Value *args[] = {Builder.CreateBitCast(out.getPointer(), VoidPtrTy),
+                         Builder.CreateBitCast(P, VoidPtrTy),
----------------
ille-apple wrote:

Ah, this is an artifact of the change having originally been written in 2020.  Looks like I can just drop the bitcast.  I don't think address-space differences are possible.

https://github.com/llvm/llvm-project/pull/89475