[PATCH] D32210: [Sema][ObjC] Add support for attribute "noescape"

[Akira Hatanaka via Phabricator via cfe-commits]

ahatanak updated this revision to Diff 96637.
ahatanak marked 4 inline comments as done.
ahatanak added a comment.

Address review comments.


https://reviews.llvm.org/D32210

Files:
  include/clang/Basic/Attr.td
  include/clang/Basic/AttrDocs.td
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaDeclAttr.cpp
  test/SemaObjCXX/noescape.mm


Index: test/SemaObjCXX/noescape.mm
===================================================================
--- /dev/null
+++ test/SemaObjCXX/noescape.mm
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -fblocks -std=c++11 %s
+
+typedef void (^BlockTy)();
+
+void noescapeFunc0(id, __attribute__((noescape)) BlockTy);
+void noescapeFunc1(id, [[clang::noescape]] BlockTy);
+void invalidFunc(int __attribute__((noescape))); // expected-warning {{'noescape' attribute ignored on parameter of non-pointer type}}
+int __attribute__((noescape)) g; // expected-warning {{'noescape' attribute only applies to parameters}}
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -1516,6 +1516,19 @@
                                Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleNoEscapeAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  // noescape only applies to pointer types.
+  QualType T = cast<ParmVarDecl>(D)->getType();
+  if (!T->isAnyPointerType() && !T->isBlockPointerType() &&
+      !T->isReferenceType() && !T->isArrayType() && !T->isMemberPointerType()) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_noescape_non_pointer) << T;
+    return;
+  }
+
+  D->addAttr(::new (S.Context) NoEscapeAttr(
+      Attr.getRange(), S.Context, Attr.getAttributeSpellingListIndex()));
+}
+
 static void handleAssumeAlignedAttr(Sema &S, Decl *D,
                                     const AttributeList &Attr) {
   Expr *E = Attr.getArgAsExpr(0),
@@ -6040,6 +6053,9 @@
   case AttributeList::AT_ReturnsNonNull:
     handleReturnsNonNullAttr(S, D, Attr);
     break;
+  case AttributeList::AT_NoEscape:
+    handleNoEscapeAttr(S, D, Attr);
+    break;
   case AttributeList::AT_AssumeAligned:
     handleAssumeAlignedAttr(S, D, Attr);
     break;
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -3109,6 +3109,10 @@
   "code; pointer may be assumed to always convert to true">,
   InGroup<UndefinedBoolConversion>;
 
+def warn_attribute_noescape_non_pointer : Warning<
+  "'noescape' attribute ignored on parameter of non-pointer type %0">,
+  InGroup<IgnoredAttributes>;
+
 def warn_null_pointer_compare : Warning<
     "comparison of %select{address of|function|array}0 '%1' %select{not |}2"
     "equal to a null pointer is always %select{true|false}2">,
Index: include/clang/Basic/AttrDocs.td
===================================================================
--- include/clang/Basic/AttrDocs.td
+++ include/clang/Basic/AttrDocs.td
@@ -112,6 +112,40 @@
   }];
 }
 
+def NoEscapeDocs : Documentation {
+  let Category = DocCatVariable;
+  let Content = [{
+``noescape`` placed on a function parameter of block type is used to inform the
+compiler that the block cannot escape: that is, no reference to the block
+derived from the parameter value will survive after the function returns.
+
+For example:
+
+.. code-block:: c
+
+  typedef void (^BlockTy)();
+  BlockTy g;
+
+  void nonescapingFunc(__attribute__((noescape)) BlockTy block) {
+    block(); // OK.
+  }
+
+  void escapingFunc(__attribute__((noescape)) BlockTy block) {
+    g = block; // Not OK. g can be invoked after the function returns.
+  }
+
+  void caller() {
+    escapingFunc(^{});
+    g();
+  }
+
+The compiler may do optimizations or issue improved diagnostics using this
+knowledge. Users are responsible for making sure parameters annotated with
+``noescape`` do not actuallly escape.
+
+  }];
+}
+
 def CarriesDependencyDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -1337,6 +1337,12 @@
   let Documentation = [Undocumented];
 }
 
+def NoEscape : InheritableAttr {
+  let Spellings = [GNU<"noescape">, CXX11<"clang", "noescape">];
+  let Subjects = SubjectList<[ParmVar]>;
+  let Documentation = [NoEscapeDocs];
+}
+
 def AssumeAligned : InheritableAttr {
   let Spellings = [GCC<"assume_aligned">];
   let Subjects = SubjectList<[ObjCMethod, Function]>;

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