[PATCH] D57626: Disallow trivial_abi on a class if all copy and move constructors are deleted

[Akira Hatanaka via Phabricator via cfe-commits]

ahatanak created this revision.
ahatanak added reviewers: rsmith, rjmccall, aaron.ballman.
ahatanak added a project: clang.
Herald added subscribers: dexonsmith, jkorous.

Instead of forcing the class to be passed in registers, which was what r350920 did, issue a warning and inform the user that the attribute cannot be used.

For more background, see this discussion: http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20190128/259907.html

This fixes PR39683.

rdar://problem/47308221


Repository:
  rC Clang

https://reviews.llvm.org/D57626

Files:
  include/clang/Basic/AttrDocs.td
  lib/Sema/SemaDeclCXX.cpp
  test/SemaObjCXX/attr-trivial-abi.mm


Index: test/SemaObjCXX/attr-trivial-abi.mm
===================================================================
--- test/SemaObjCXX/attr-trivial-abi.mm
+++ test/SemaObjCXX/attr-trivial-abi.mm
@@ -95,3 +95,36 @@
 };
 
 S17<int> s17;
+
+namespace deletedCopyMoveConstructor {
+  struct __attribute__((trivial_abi)) CopyMoveDeleted { // expected-warning {{'trivial_abi' cannot be applied to 'CopyMoveDeleted'}}
+    CopyMoveDeleted(const CopyMoveDeleted &) = delete;
+    CopyMoveDeleted(CopyMoveDeleted &&) = delete;
+  };
+
+  struct __attribute__((trivial_abi)) S18 { // expected-warning {{'trivial_abi' cannot be applied to 'S18'}}
+    CopyMoveDeleted a;
+    S18(const S18 &);
+    S18(S18 &&);
+  };
+
+  struct __attribute__((trivial_abi)) CopyDeleted {
+    CopyDeleted(const CopyDeleted &) = delete;
+    CopyDeleted(CopyDeleted &&) = default;
+  };
+
+  struct __attribute__((trivial_abi)) MoveDeleted {
+    MoveDeleted(const MoveDeleted &) = default;
+    MoveDeleted(MoveDeleted &&) = delete;
+  };
+
+  struct __attribute__((trivial_abi)) S19 { // expected-warning {{'trivial_abi' cannot be applied to 'S19'}}
+    CopyDeleted a;
+    MoveDeleted b;
+  };
+
+  // This is fine since the move constructor isn't deleted.
+  struct __attribute__((trivial_abi)) S20 {
+    int &&a; // a member of rvalue reference type deletes the copy constructor.
+  };
+}
Index: lib/Sema/SemaDeclCXX.cpp
===================================================================
--- lib/Sema/SemaDeclCXX.cpp
+++ lib/Sema/SemaDeclCXX.cpp
@@ -7868,6 +7868,25 @@
     RD.dropAttr<TrivialABIAttr>();
   };
 
+  // Ill-formed if the copy and move constructors are deleted.
+  auto HasNonDeletedCopyOrMoveConstructor = [&]() {
+    if (RD.needsImplicitCopyConstructor() &&
+        !RD.defaultedCopyConstructorIsDeleted())
+      return true;
+    if (RD.needsImplicitMoveConstructor() &&
+        !RD.defaultedMoveConstructorIsDeleted())
+      return true;
+    for (const CXXConstructorDecl *CD : RD.ctors())
+      if (CD->isCopyOrMoveConstructor() && !CD->isDeleted())
+        return true;
+    return false;
+  };
+
+  if (!HasNonDeletedCopyOrMoveConstructor()) {
+    PrintDiagAndRemoveAttr();
+    return;
+  }
+
   // Ill-formed if the struct has virtual functions.
   if (RD.isPolymorphic()) {
     PrintDiagAndRemoveAttr();
Index: include/clang/Basic/AttrDocs.td
===================================================================
--- include/clang/Basic/AttrDocs.td
+++ include/clang/Basic/AttrDocs.td
@@ -2566,6 +2566,7 @@
 Attribute ``trivial_abi`` has no effect in the following cases:
 
 - The class directly declares a virtual base or virtual methods.
+- The class doesn't have a copy or move constructor that isn't deleted.
 - The class has a base class that is non-trivial for the purposes of calls.
 - The class has a non-static data member whose type is non-trivial for the purposes of calls, which includes:
 


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