[clang] Add no_builtin attribute

gchatelet · gchatelet · commit 98f3151a7dde · 2019-10-29T15:50:29.000+01:00
Summary: This is a follow up on https://reviews.llvm.org/D61634 This patch is simpler and only adds the no_builtin attribute. Reviewers: tejohnson, courbet, theraven, t.p.northover, jdoerfert Subscribers: mgrang, cfe-commits Tags: #clang Differential Revision: https://reviews.llvm.org/D68028 This is a re-submit after it got reverted in https://reviews.llvm.org/rGbd8791610948 since the breakage doesn't seem to come from this patch.
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
@@ -2031,6 +2031,10 @@ class FunctionDecl : public DeclaratorDecl,
   ///
   /// This does not determine whether the function has been defined (e.g., in a
   /// previous definition); for that information, use isDefined.
+  ///
+  /// Note: the function declaration does not become a definition until the
+  /// parser reaches the definition, if called before, this function will return
+  /// `false`.
   bool isThisDeclarationADefinition() const {
     return isDeletedAsWritten() || isDefaulted() || Body || hasSkippedBody() ||
            isLateTemplateParsed() || willHaveBody() || hasDefiningAttr();
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
@@ -3427,3 +3427,10 @@ def ObjCExternallyRetained : InheritableAttr {
   let Subjects = SubjectList<[NonParmVar, Function, Block, ObjCMethod]>;
   let Documentation = [ObjCExternallyRetainedDocs];
 }
+
+def NoBuiltin : Attr {
+  let Spellings = [Clang<"no_builtin">];
+  let Args = [VariadicStringArgument<"BuiltinNames">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [NoBuiltinDocs];
+}
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
@@ -4413,3 +4413,40 @@ and is not a general mechanism for declaring arbitrary aliases for
 clang builtin functions.
   }];
 }
+
+def NoBuiltinDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+.. Note:: This attribute is not yet fully implemented, it is validated but has
+no effect on the generated code.
+
+The ``__attribute__((no_builtin))`` is similar to the ``-fno-builtin`` flag
+except it is specific to the body of a function. The attribute may also be
+applied to a virtual function but has no effect on the behavior of overriding
+functions in a derived class.
+
+It accepts one or more strings corresponding to the specific names of the
+builtins to disable (e.g. "memcpy", "memset").
+If the attribute is used without parameters it will disable all buitins at
+once.
+
+.. code-block:: c++
+
+  // The compiler is not allowed to add any builtin to foo's body.
+  void foo(char* data, size_t count) __attribute__((no_builtin)) {
+    // The compiler is not allowed to convert the loop into
+    // `__builtin_memset(data, 0xFE, count);`.
+    for (size_t i = 0; i < count; ++i)
+      data[i] = 0xFE;
+  }
+
+  // The compiler is not allowed to add the `memcpy` builtin to bar's body.
+  void bar(char* data, size_t count) __attribute__((no_builtin("memcpy"))) {
+    // The compiler is allowed to convert the loop into
+    // `__builtin_memset(data, 0xFE, count);` but cannot generate any
+    // `__builtin_memcpy`
+    for (size_t i = 0; i < count; ++i)
+      data[i] = 0xFE;
+  }
+  }];
+}
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3604,6 +3604,15 @@ def err_attribute_overloadable_no_prototype : Error<
 def err_attribute_overloadable_multiple_unmarked_overloads : Error<
   "at most one overload for a given name may lack the 'overloadable' "
   "attribute">;
+def warn_attribute_no_builtin_invalid_builtin_name : Warning<
+  "'%0' is not a valid builtin name for %1">,
+  InGroup<DiagGroup<"invalid-no-builtin-names">>;
+def err_attribute_no_builtin_wildcard_or_builtin_name : Error<
+  "empty %0 cannot be composed with named ones">;
+def err_attribute_no_builtin_on_non_definition : Error<
+  "%0 attribute is permitted on definitions only">;
+def err_attribute_no_builtin_on_defaulted_deleted_function : Error<
+  "%0 attribute has no effect on defaulted or deleted functions">;
 def warn_ns_attribute_wrong_return_type : Warning<
   "%0 attribute only applies to %select{functions|methods|properties}1 that "
   "return %select{an Objective-C object|a pointer|a non-retainable pointer}2">,
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
@@ -1853,11 +1853,27 @@ void CodeGenModule::ConstructAttributeList(
     if (const FunctionDecl *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
       AddAttributesFromFunctionProtoType(
           getContext(), FuncAttrs, Fn->getType()->getAs<FunctionProtoType>());
-      // Don't use [[noreturn]] or _Noreturn for a call to a virtual function.
-      // These attributes are not inherited by overloads.
       const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Fn);
-      if (Fn->isNoReturn() && !(AttrOnCallSite && MD && MD->isVirtual()))
-        FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
+      const bool IsVirtualCall = MD && MD->isVirtual();
+      // Don't use [[noreturn]], _Noreturn or [[no_builtin]] for a call to a
+      // virtual function. These attributes are not inherited by overloads.
+      if (!(AttrOnCallSite && IsVirtualCall)) {
+        if (Fn->isNoReturn())
+          FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
+
+        if (const auto *NBA = TargetDecl->getAttr<NoBuiltinAttr>()) {
+          bool HasWildcard = llvm::is_contained(NBA->builtinNames(), "*");
+          if (HasWildcard)
+            FuncAttrs.addAttribute("no-builtins");
+          else
+            for (StringRef BuiltinName : NBA->builtinNames()) {
+              SmallString<32> AttributeName;
+              AttributeName += "no-builtin-";
+              AttributeName += BuiltinName;
+              FuncAttrs.addAttribute(AttributeName);
+            }
+        }
+      }
     }
 
     // 'const', 'pure' and 'noalias' attributed functions are also nounwind.
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
@@ -9529,6 +9529,29 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     }
   }
 
+  // Diagnose no_builtin attribute on function declaration that are not a
+  // definition.
+  // FIXME: We should really be doing this in
+  // SemaDeclAttr.cpp::handleNoBuiltinAttr, unfortunately we only have access to
+  // the FunctionDecl and at this point of the code
+  // FunctionDecl::isThisDeclarationADefinition() which always returns `false`
+  // because Sema::ActOnStartOfFunctionDef has not been called yet.
+  if (const auto *NBA = NewFD->getAttr<NoBuiltinAttr>())
+    switch (D.getFunctionDefinitionKind()) {
+    case FDK_Defaulted:
+    case FDK_Deleted:
+      Diag(NBA->getLocation(),
+           diag::err_attribute_no_builtin_on_defaulted_deleted_function)
+          << NBA->getSpelling();
+      break;
+    case FDK_Declaration:
+      Diag(NBA->getLocation(), diag::err_attribute_no_builtin_on_non_definition)
+          << NBA->getSpelling();
+      break;
+    case FDK_Definition:
+      break;
+    }
+
   return NewFD;
 }
 
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1069,6 +1069,56 @@ static void handleDiagnoseIfAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
       S.Context, AL, Cond, Msg, DiagType, ArgDependent, cast<NamedDecl>(D)));
 }
 
+static void handleNoBuiltinAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  static constexpr const StringRef kWildcard = "*";
+
+  llvm::SmallVector<StringRef, 16> Names;
+  bool HasWildcard = false;
+
+  const auto AddBuiltinName = [&Names, &HasWildcard](StringRef Name) {
+    if (Name == kWildcard)
+      HasWildcard = true;
+    Names.push_back(Name);
+  };
+
+  // Add previously defined attributes.
+  if (const auto *NBA = D->getAttr<NoBuiltinAttr>())
+    for (StringRef BuiltinName : NBA->builtinNames())
+      AddBuiltinName(BuiltinName);
+
+  // Add current attributes.
+  if (AL.getNumArgs() == 0)
+    AddBuiltinName(kWildcard);
+  else
+    for (unsigned I = 0, E = AL.getNumArgs(); I != E; ++I) {
+      StringRef BuiltinName;
+      SourceLocation LiteralLoc;
+      if (!S.checkStringLiteralArgumentAttr(AL, I, BuiltinName, &LiteralLoc))
+        return;
+
+      if (Builtin::Context::isBuiltinFunc(BuiltinName.data()))
+        AddBuiltinName(BuiltinName);
+      else
+        S.Diag(LiteralLoc, diag::warn_attribute_no_builtin_invalid_builtin_name)
+            << BuiltinName << AL.getAttrName()->getName();
+    }
+
+  // Repeating the same attribute is fine.
+  llvm::sort(Names);
+  Names.erase(std::unique(Names.begin(), Names.end()), Names.end());
+
+  // Empty no_builtin must be on its own.
+  if (HasWildcard && Names.size() > 1)
+    S.Diag(D->getLocation(),
+           diag::err_attribute_no_builtin_wildcard_or_builtin_name)
+        << AL.getAttrName()->getName();
+
+  if (D->hasAttr<NoBuiltinAttr>())
+    D->dropAttr<NoBuiltinAttr>();
+  D->addAttr(::new (S.Context)
+                 NoBuiltinAttr(S.Context, AL, Names.data(), Names.size()));
+}
+
 static void handlePassObjectSizeAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (D->hasAttr<PassObjectSizeAttr>()) {
     S.Diag(D->getBeginLoc(), diag::err_attribute_only_once_per_parameter) << AL;
@@ -6608,6 +6658,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_DiagnoseIf:
     handleDiagnoseIfAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_NoBuiltin:
+    handleNoBuiltinAttr(S, D, AL);
+    break;
   case ParsedAttr::AT_ExtVectorType:
     handleExtVectorTypeAttr(S, D, AL);
     break;
diff --git a/clang/test/CodeGen/no-builtin.cpp b/clang/test/CodeGen/no-builtin.cpp
@@ -0,0 +1,64 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -S -emit-llvm -o - %s | FileCheck %s
+
+// CHECK-LABEL: define void @foo_no_mempcy() #0
+extern "C" void foo_no_mempcy() __attribute__((no_builtin("memcpy"))) {}
+
+// CHECK-LABEL: define void @foo_no_mempcy_twice() #0
+extern "C" void foo_no_mempcy_twice() __attribute__((no_builtin("memcpy"))) __attribute__((no_builtin("memcpy"))) {}
+
+// CHECK-LABEL: define void @foo_no_builtins() #1
+extern "C" void foo_no_builtins() __attribute__((no_builtin)) {}
+
+// CHECK-LABEL: define void @foo_no_mempcy_memset() #2
+extern "C" void foo_no_mempcy_memset() __attribute__((no_builtin("memset", "memcpy"))) {}
+
+// CHECK-LABEL: define void @separate_attrs() #2
+extern "C" void separate_attrs() __attribute__((no_builtin("memset"))) __attribute__((no_builtin("memcpy"))) {}
+
+// CHECK-LABEL: define void @separate_attrs_ordering() #2
+extern "C" void separate_attrs_ordering() __attribute__((no_builtin("memcpy"))) __attribute__((no_builtin("memset"))) {}
+
+struct A {
+  virtual int foo() const __attribute__((no_builtin("memcpy"))) { return 1; }
+  virtual ~A();
+};
+
+struct B : public A {
+  int foo() const override __attribute__((no_builtin("memmove"))) { return 2; }
+  virtual ~B();
+};
+
+// CHECK-LABEL: define void @call_a_foo(%struct.A* %a) #3
+extern "C" void call_a_foo(A *a) {
+  // CHECK: %call = call i32 %2(%struct.A* %0)
+  a->foo(); // virtual call is not annotated
+}
+
+// CHECK-LABEL: define void @call_b_foo(%struct.B* %b) #3
+extern "C" void call_b_foo(B *b) {
+  // CHECK: %call = call i32 %2(%struct.B* %0)
+  b->foo(); // virtual call is not annotated
+}
+
+// CHECK-LABEL: define void @call_foo_no_mempcy() #3
+extern "C" void call_foo_no_mempcy() {
+  // CHECK: call void @foo_no_mempcy() #6
+  foo_no_mempcy(); // call gets annotated with "no-builtin-memcpy"
+}
+
+A::~A() {} // Anchoring A so A::foo() gets generated
+B::~B() {} // Anchoring B so B::foo() gets generated
+
+// CHECK-LABEL: define linkonce_odr i32 @_ZNK1A3fooEv(%struct.A* %this) unnamed_addr #0 comdat align 2
+// CHECK-LABEL: define linkonce_odr i32 @_ZNK1B3fooEv(%struct.B* %this) unnamed_addr #5 comdat align 2
+
+// CHECK:     attributes #0 = {{{.*}}"no-builtin-memcpy"{{.*}}}
+// CHECK-NOT: attributes #0 = {{{.*}}"no-builtin-memmove"{{.*}}}
+// CHECK-NOT: attributes #0 = {{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK:     attributes #1 = {{{.*}}"no-builtins"{{.*}}}
+// CHECK:     attributes #2 = {{{.*}}"no-builtin-memcpy"{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK-NOT: attributes #2 = {{{.*}}"no-builtin-memmove"{{.*}}}
+// CHECK:     attributes #5 = {{{.*}}"no-builtin-memmove"{{.*}}}
+// CHECK-NOT: attributes #5 = {{{.*}}"no-builtin-memcpy"{{.*}}}
+// CHECK-NOT: attributes #5 = {{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK:     attributes #6 = { "no-builtin-memcpy" }
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -75,6 +75,7 @@
 // CHECK-NEXT: NSConsumed (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: NSConsumesSelf (SubjectMatchRule_objc_method)
 // CHECK-NEXT: Naked (SubjectMatchRule_function)
+// CHECK-NEXT: NoBuiltin (SubjectMatchRule_function)
 // CHECK-NEXT: NoCommon (SubjectMatchRule_variable)
 // CHECK-NEXT: NoDebug (SubjectMatchRule_type_alias, SubjectMatchRule_hasType_functionType, SubjectMatchRule_objc_method, SubjectMatchRule_variable_not_is_parameter)
 // CHECK-NEXT: NoDestroy (SubjectMatchRule_variable)
diff --git a/clang/test/Sema/no-builtin.cpp b/clang/test/Sema/no-builtin.cpp
@@ -0,0 +1,51 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s
+
+/// Prevent use of all builtins.
+void valid_attribute_all_1() __attribute__((no_builtin)) {}
+void valid_attribute_all_2() __attribute__((no_builtin())) {}
+
+/// Prevent use of specific builtins.
+void valid_attribute_function() __attribute__((no_builtin("memcpy"))) {}
+void valid_attribute_functions() __attribute__((no_builtin("memcpy"))) __attribute__((no_builtin("memcmp"))) {}
+
+/// Many times the same builtin is fine.
+void many_attribute_function_1() __attribute__((no_builtin)) __attribute__((no_builtin)) {}
+void many_attribute_function_2() __attribute__((no_builtin("memcpy"))) __attribute__((no_builtin("memcpy"))) {}
+void many_attribute_function_3() __attribute__((no_builtin("memcpy", "memcpy"))) {}
+void many_attribute_function_4() __attribute__((no_builtin("memcpy", "memcpy"))) __attribute__((no_builtin("memcpy"))) {}
+
+/// Invalid builtin name.
+void invalid_builtin() __attribute__((no_builtin("not_a_builtin"))) {}
+// expected-warning@-1 {{'not_a_builtin' is not a valid builtin name for no_builtin}}
+
+/// Can't use bare no_builtin with a named one.
+void wildcard_and_functionname() __attribute__((no_builtin)) __attribute__((no_builtin("memcpy"))) {}
+// expected-error@-1 {{empty no_builtin cannot be composed with named ones}}
+
+/// Can't attach attribute to a variable.
+int __attribute__((no_builtin)) variable;
+// expected-warning@-1 {{'no_builtin' attribute only applies to functions}}
+
+/// Can't attach attribute to a declaration.
+void nobuiltin_on_declaration() __attribute__((no_builtin));
+// expected-error@-1 {{no_builtin attribute is permitted on definitions only}}
+
+struct S {
+  /// Can't attach attribute to a defaulted function,
+  S()
+  __attribute__((no_builtin)) = default;
+  // expected-error@-1 {{no_builtin attribute has no effect on defaulted or deleted functions}}
+
+  /// Can't attach attribute to a deleted function,
+  S(const S &)
+  __attribute__((no_builtin)) = delete;
+  // expected-error@-1 {{no_builtin attribute has no effect on defaulted or deleted functions}}
+
+  void whatever() __attribute__((no_builtin("memcpy")));
+  // expected-error@-1 {{no_builtin attribute is permitted on definitions only}}
+};
+
+/// Can't attach attribute to an aliased function.
+void alised_function() {}
+void aliasing_function() __attribute__((no_builtin)) __attribute__((alias("alised_function")));
+// expected-error@-1 {{no_builtin attribute is permitted on definitions only}}
