Tighten up the set of operator new/operator delete calls we're permitted to

optimize, to follow the permissions granted in N3664. Under those rules, only
calls generated by new-expressions and delete-expressions are permitted to be
optimized, and direct calls to ::operator new and ::operator delete must be
treated as normal calls.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186799 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/Decl.h

@@ -1720,6 +1720,21 @@ public:
   /// This function must be an allocation or deallocation function.
   bool isReservedGlobalPlacementOperator() const;
 
+  /// \brief Determines whether this function is one of the replaceable
+  /// global allocation functions:
+  ///    void *operator new(size_t);
+  ///    void *operator new(size_t, const std::nothrow_t &) noexcept;
+  ///    void *operator new[](size_t);
+  ///    void *operator new[](size_t, const std::nothrow_t &) noexcept;
+  ///    void operator delete(void *) noexcept;
+  ///    void operator delete(void *, const std::nothrow_t &) noexcept;
+  ///    void operator delete[](void *) noexcept;
+  ///    void operator delete[](void *, const std::nothrow_t &) noexcept;
+  /// These functions have special behavior under C++1y [expr.new]:
+  ///    An implementation is allowed to omit a call to a replaceable global
+  ///    allocation function. [...]
+  bool isReplaceableGlobalAllocationFunction() const;
+
   /// Compute the language linkage.
   LanguageLinkage getLanguageLinkage() const;
 

lib/AST/Decl.cpp

@@ -2132,13 +2132,18 @@ void FunctionDecl::setPure(bool P) {
       Parent->markedVirtualFunctionPure();
 }
 
+template<std::size_t Len>
+static bool isNamed(const NamedDecl *ND, const char (&Str)[Len]) {
+  IdentifierInfo *II = ND->getIdentifier();
+  return II && II->isStr(Str);
+}
+
 bool FunctionDecl::isMain() const {
   const TranslationUnitDecl *tunit =
     dyn_cast<TranslationUnitDecl>(getDeclContext()->getRedeclContext());
   return tunit &&
          !tunit->getASTContext().getLangOpts().Freestanding &&
-         getIdentifier() &&
-         getIdentifier()->isStr("main");
+         isNamed(this, "main");
 }
 
 bool FunctionDecl::isReservedGlobalPlacementOperator() const {
@@ -2163,6 +2168,47 @@ bool FunctionDecl::isReservedGlobalPlacementOperator() const {
   return (proto->getArgType(1).getCanonicalType() == Context.VoidPtrTy);
 }
 
+static bool isNamespaceStd(const DeclContext *DC) {
+  const NamespaceDecl *ND = dyn_cast<NamespaceDecl>(DC->getRedeclContext());
+  return ND && isNamed(ND, "std") &&
+         ND->getParent()->getRedeclContext()->isTranslationUnit();
+}
+
+bool FunctionDecl::isReplaceableGlobalAllocationFunction() const {
+  if (getDeclName().getNameKind() != DeclarationName::CXXOperatorName)
+    return false;
+  if (getDeclName().getCXXOverloadedOperator() != OO_New &&
+      getDeclName().getCXXOverloadedOperator() != OO_Delete &&
+      getDeclName().getCXXOverloadedOperator() != OO_Array_New &&
+      getDeclName().getCXXOverloadedOperator() != OO_Array_Delete)
+    return false;
+
+  if (isa<CXXRecordDecl>(getDeclContext()))
+    return false;
+  assert(getDeclContext()->getRedeclContext()->isTranslationUnit());
+
+  const FunctionProtoType *FPT = getType()->castAs<FunctionProtoType>();
+  if (FPT->getNumArgs() > 2 || FPT->isVariadic())
+    return false;
+
+  // If this is a single-parameter function, it must be a replaceable global
+  // allocation or deallocation function.
+  if (FPT->getNumArgs() == 1)
+    return true;
+
+  // Otherwise, we're looking for a second parameter whose type is
+  // 'const std::nothrow_t &'.
+  QualType Ty = FPT->getArgType(1);
+  if (!Ty->isReferenceType())
+    return false;
+  Ty = Ty->getPointeeType();
+  if (Ty.getCVRQualifiers() != Qualifiers::Const)
+    return false;
+  // FIXME: Recognise nothrow_t in an inline namespace inside std?
+  const CXXRecordDecl *RD = Ty->getAsCXXRecordDecl();
+  return RD && isNamed(RD, "nothrow_t") && isNamespaceStd(RD->getDeclContext());
+}
+
 LanguageLinkage FunctionDecl::getLanguageLinkage() const {
   // Users expect to be able to write
   // extern "C" void *__builtin_alloca (size_t);

lib/CodeGen/CGExprCXX.cpp

@@ -1002,6 +1002,38 @@ static void EmitNewInitializer(CodeGenFunction &CGF, const CXXNewExpr *E,
   StoreAnyExprIntoOneUnit(CGF, Init, E->getAllocatedType(), NewPtr);
 }
 
+/// Emit a call to an operator new or operator delete function, as implicitly
+/// created by new-expressions and delete-expressions.
+static RValue EmitNewDeleteCall(CodeGenFunction &CGF,
+                                const FunctionDecl *Callee,
+                                const FunctionProtoType *CalleeType,
+                                const CallArgList &Args) {
+  llvm::Instruction *CallOrInvoke;
+  RValue RV =
+      CGF.EmitCall(CGF.CGM.getTypes().arrangeFreeFunctionCall(Args, CalleeType),
+                   CGF.CGM.GetAddrOfFunction(Callee), ReturnValueSlot(), Args,
+                   Callee, &CallOrInvoke);
+
+  /// C++1y [expr.new]p10:
+  ///   [In a new-expression,] an implementation is allowed to omit a call
+  ///   to a replaceable global allocation function.
+  ///
+  /// We model such elidable calls with the 'builtin' attribute.
+  if (Callee->isReplaceableGlobalAllocationFunction()) {
+    // FIXME: Add addAttribute to CallSite.
+    if (llvm::CallInst *CI = dyn_cast<llvm::CallInst>(CallOrInvoke))
+      CI->addAttribute(llvm::AttributeSet::FunctionIndex,
+                       llvm::Attribute::Builtin);
+    else if (llvm::InvokeInst *II = dyn_cast<llvm::InvokeInst>(CallOrInvoke))
+      II->addAttribute(llvm::AttributeSet::FunctionIndex,
+                       llvm::Attribute::Builtin);
+    else
+      llvm_unreachable("unexpected kind of call instruction");
+  }
+
+  return RV;
+}
+
 namespace {
   /// A cleanup to call the given 'operator delete' function upon
   /// abnormal exit from a new expression.
@@ -1051,9 +1083,7 @@ namespace {
         DeleteArgs.add(getPlacementArgs()[I], *AI++);
 
       // Call 'operator delete'.
-      CGF.EmitCall(CGF.CGM.getTypes().arrangeFreeFunctionCall(DeleteArgs, FPT),
-                   CGF.CGM.GetAddrOfFunction(OperatorDelete),
-                   ReturnValueSlot(), DeleteArgs, OperatorDelete);
+      EmitNewDeleteCall(CGF, OperatorDelete, FPT, DeleteArgs);
     }
   };
 
@@ -1112,9 +1142,7 @@ namespace {
       }
 
       // Call 'operator delete'.
-      CGF.EmitCall(CGF.CGM.getTypes().arrangeFreeFunctionCall(DeleteArgs, FPT),
-                   CGF.CGM.GetAddrOfFunction(OperatorDelete),
-                   ReturnValueSlot(), DeleteArgs, OperatorDelete);
+      EmitNewDeleteCall(CGF, OperatorDelete, FPT, DeleteArgs);
     }
   };
 }
@@ -1227,10 +1255,7 @@ llvm::Value *CodeGenFunction::EmitCXXNewExpr(const CXXNewExpr *E) {
     // TODO: kill any unnecessary computations done for the size
     // argument.
   } else {
-    RV = EmitCall(CGM.getTypes().arrangeFreeFunctionCall(allocatorArgs,
-                                                         allocatorType),
-                  CGM.GetAddrOfFunction(allocator), ReturnValueSlot(),
-                  allocatorArgs, allocator);
+    RV = EmitNewDeleteCall(*this, allocator, allocatorType, allocatorArgs);
   }
 
   // Emit a null check on the allocation result if the allocation
@@ -1350,9 +1375,7 @@ void CodeGenFunction::EmitDeleteCall(const FunctionDecl *DeleteFD,
     DeleteArgs.add(RValue::get(Size), SizeTy);
 
   // Emit the call to delete.
-  EmitCall(CGM.getTypes().arrangeFreeFunctionCall(DeleteArgs, DeleteFTy),
-           CGM.GetAddrOfFunction(DeleteFD), ReturnValueSlot(), 
-           DeleteArgs, DeleteFD);
+  EmitNewDeleteCall(*this, DeleteFD, DeleteFTy, DeleteArgs);
 }
 
 namespace {
@@ -1508,9 +1531,7 @@ namespace {
       }
 
       // Emit the call to delete.
-      CGF.EmitCall(CGF.getTypes().arrangeFreeFunctionCall(Args, DeleteFTy),
-                   CGF.CGM.GetAddrOfFunction(OperatorDelete),
-                   ReturnValueSlot(), Args, OperatorDelete);
+      EmitNewDeleteCall(CGF, OperatorDelete, DeleteFTy, Args);
     }
   };
 }

lib/CodeGen/CodeGenModule.cpp

@@ -744,6 +744,12 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD,
 
   if (const SectionAttr *SA = FD->getAttr<SectionAttr>())
     F->setSection(SA->getName());
+
+  // A replaceable global allocation function does not act like a builtin by
+  // default, only if it is invoked by a new-expression or delete-expression.
+  if (FD->isReplaceableGlobalAllocationFunction())
+    F->addAttribute(llvm::AttributeSet::FunctionIndex,
+                    llvm::Attribute::NoBuiltin);
 }
 
 void CodeGenModule::AddUsedGlobal(llvm::GlobalValue *GV) {

test/CodeGenCXX/new.cpp

@@ -2,9 +2,24 @@
 
 typedef __typeof__(sizeof(0)) size_t;
 
+// Ensure that this declaration doesn't cause operator new to lose its
+// 'noalias' attribute.
+void *operator new[](size_t);
+
 void t1() {
-  int* a = new int;
+  delete new int;
+  delete [] new int [3];
+}
+
+// CHECK: declare noalias i8* @_Znwm(i64) [[ATTR_NOBUILTIN:#[^ ]*]]
+// CHECK: declare void @_ZdlPv(i8*) [[ATTR_NOBUILTIN_NOUNWIND:#[^ ]*]]
+// CHECK: declare noalias i8* @_Znam(i64) [[ATTR_NOBUILTIN]]
+// CHECK: declare void @_ZdaPv(i8*) [[ATTR_NOBUILTIN_NOUNWIND]]
+
+namespace std {
+  struct nothrow_t {};
 }
+std::nothrow_t nothrow;
 
 // Declare the reserved placement operators.
 void *operator new(size_t, void*) throw();
@@ -12,6 +27,13 @@ void operator delete(void*, void*) throw();
 void *operator new[](size_t, void*) throw();
 void operator delete[](void*, void*) throw();
 
+// Declare the replaceable global allocation operators.
+void *operator new(size_t, const std::nothrow_t &) throw();
+void *operator new[](size_t, const std::nothrow_t &) throw();
+void operator delete(void *, const std::nothrow_t &) throw();
+void operator delete[](void *, const std::nothrow_t &) throw();
+
+
 void t2(int* a) {
   int* b = new (a) int;
 }
@@ -77,10 +99,6 @@ void t8(int n) {
   new U[n];
 }
 
-// noalias
-// CHECK: declare noalias i8* @_Znam
-void *operator new[](size_t);
-
 void t9() {
   bool b;
 
@@ -260,3 +278,63 @@ namespace PR13380 {
   // CHECK-NEXT: call void @_ZN7PR133801BC1Ev
   void* f() { return new B[2](); }
 }
+
+struct MyPlacementType {} mpt;
+void *operator new(size_t, MyPlacementType);
+
+namespace N3664 {
+  struct S { S() throw(int); };
+
+  // CHECK-LABEL: define void @_ZN5N36641fEv
+  void f() {
+    // CHECK: call noalias i8* @_Znwm(i64 4) [[ATTR_BUILTIN_NEW:#[^ ]*]]
+    int *p = new int;
+    // CHECK: call void @_ZdlPv({{.*}}) [[ATTR_BUILTIN_DELETE:#[^ ]*]]
+    delete p;
+
+    // CHECK: call noalias i8* @_Znam(i64 12) [[ATTR_BUILTIN_NEW]]
+    int *q = new int[3];
+    // CHECK: call void @_ZdaPv({{.*}}) [[ATTR_BUILTIN_DELETE]]
+    delete [] p;
+
+    // CHECK: call i8* @_ZnamRKSt9nothrow_t(i64 3, {{.*}}) [[ATTR_BUILTIN_NOTHROW_NEW:#[^ ]*]]
+    (void) new (nothrow) S[3];
+
+    // CHECK: call i8* @_Znwm15MyPlacementType(i64 4){{$}}
+    (void) new (mpt) int;
+  }
+
+  // FIXME: Can we mark this noalias?
+  // CHECK: declare i8* @_ZnamRKSt9nothrow_t(i64, {{.*}}) [[ATTR_NOBUILTIN_NOUNWIND]]
+
+  // CHECK-LABEL: define void @_ZN5N36641gEv
+  void g() {
+    // It's OK for there to be attributes here, so long as we don't have a
+    // 'builtin' attribute.
+    // CHECK: call noalias i8* @_Znwm(i64 4){{$}}
+    int *p = (int*)operator new(4);
+    // CHECK: call void @_ZdlPv({{.*}}) [[ATTR_NOUNWIND:#[^ ]*]]
+    operator delete(p);
+
+    // CHECK: call noalias i8* @_Znam(i64 12){{$}}
+    int *q = (int*)operator new[](12);
+    // CHECK: call void @_ZdaPv({{.*}}) [[ATTR_NOUNWIND]]
+    operator delete [](p);
+
+    // CHECK: call i8* @_ZnamRKSt9nothrow_t(i64 3, {{.*}}) [[ATTR_NOUNWIND]]
+    (void) operator new[](3, nothrow);
+  }
+}
+
+// CHECK-DAG: attributes [[ATTR_NOBUILTIN]] = {{[{].*}} nobuiltin {{.*[}]}}
+// CHECK-DAG: attributes [[ATTR_NOBUILTIN_NOUNWIND]] = {{[{].*}} nobuiltin nounwind {{.*[}]}}
+
+// CHECK: attributes [[ATTR_NOUNWIND]] =
+// CHECK-NOT: builtin
+// CHECK-NOT: attributes
+// CHECK: nounwind
+// CHECK-NOT: builtin
+// CHECK: attributes
+
+// CHECK-DAG: attributes [[ATTR_BUILTIN_NEW]] = {{[{].*}} builtin {{.*[}]}}
+// CHECK-DAG: attributes [[ATTR_BUILTIN_DELETE]] = {{[{].*}} builtin {{.*[}]}}

www/cxx_status.html

@@ -467,7 +467,7 @@ available.</p>
     <tr>
       <td>Clarifying memory allocation</td>
       <td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3664.html">N3664</a></td>
-      <td class="partial" align="center">Partial</td>
+      <td class="svn" align="center">SVN</td>
     </tr>
 </table>