[clang] Implement lifetime analysis for lifetime_capture_by(X)

clang/include/clang/Basic/DiagnosticGroups.td

@@ -453,6 +453,7 @@ def ShiftOpParentheses: DiagGroup<"shift-op-parentheses">;
 def OverloadedShiftOpParentheses: DiagGroup<"overloaded-shift-op-parentheses">;
 def DanglingAssignment: DiagGroup<"dangling-assignment">;
 def DanglingAssignmentGsl : DiagGroup<"dangling-assignment-gsl">;
+def DanglingCapture : DiagGroup<"dangling-capture">;
 def DanglingElse: DiagGroup<"dangling-else">;
 def DanglingField : DiagGroup<"dangling-field">;
 def DanglingInitializerList : DiagGroup<"dangling-initializer-list">;
@@ -462,6 +463,7 @@ def ReturnStackAddress : DiagGroup<"return-stack-address">;
 def : DiagGroup<"return-local-addr", [ReturnStackAddress]>;
 def Dangling : DiagGroup<"dangling", [DanglingAssignment,
                                       DanglingAssignmentGsl,
+                                      DanglingCapture,
                                       DanglingField,
                                       DanglingInitializerList,
                                       DanglingGsl,

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10132,10 +10132,11 @@ def err_lifetimebound_ctor_dtor : Error<
   "%select{constructor|destructor}0">;
 def err_lifetimebound_parameter_void_return_type : Error<
   "'lifetimebound' attribute cannot be applied to a parameter of a function "
-  "that returns void">;
+  "that returns void; did you mean 'lifetime_capture_by(X)'">;
 def err_lifetimebound_implicit_object_parameter_void_return_type : Error<
   "'lifetimebound' attribute cannot be applied to an implicit object "
-  "parameter of a function that returns void">;
+  "parameter of a function that returns void; "
+  "did you mean 'lifetime_capture_by(X)'">;
 
 // CHECK: returning address/reference of stack memory
 def warn_ret_stack_addr_ref : Warning<
@@ -10230,6 +10231,12 @@ def warn_dangling_pointer_assignment : Warning<
    "object backing %select{|the pointer }0%1 "
    "will be destroyed at the end of the full-expression">,
    InGroup<DanglingAssignment>;
+def warn_dangling_reference_captured : Warning<
+   "object whose reference is captured by '%0' will be destroyed at the end of "
+   "the full-expression">, InGroup<DanglingCapture>;
+def warn_dangling_reference_captured_by_unknown : Warning<
+   "object whose reference is captured will be destroyed at the end of "
+   "the full-expression">, InGroup<DanglingCapture>;
 
 // For non-floating point, expressions of the form x == x or x != x
 // should result in a warning, since these always evaluate to a constant.

clang/include/clang/Sema/Sema.h

@@ -2323,6 +2323,9 @@ class Sema final : public SemaBase {
   bool BuiltinVectorMath(CallExpr *TheCall, QualType &Res, bool FPOnly = false);
   bool BuiltinVectorToScalarMath(CallExpr *TheCall);
 
+  void checkLifetimeCaptureBy(FunctionDecl *FDecl, bool IsMemberFunction,
+                              const Expr *ThisArg, ArrayRef<const Expr *> Args);
+
   /// Handles the checks for format strings, non-POD arguments to vararg
   /// functions, NULL arguments passed to non-NULL parameters, diagnose_if
   /// attributes and AArch64 SME attributes.

clang/lib/Sema/CheckExprLifetime.cpp

@@ -45,10 +45,14 @@ enum LifetimeKind {
   /// a default member initializer), the program is ill-formed.
   LK_MemInitializer,
 
-  /// The lifetime of a temporary bound to this entity probably ends too soon,
+  /// The lifetime of a temporary bound to this entity may end too soon,
   /// because the entity is a pointer and we assign the address of a temporary
   /// object to it.
   LK_Assignment,
+
+  /// The lifetime of a temporary bound to this entity may end too soon,
+  /// because the entity may capture the reference to a temporary object.
+  LK_LifetimeCapture,
 };
 using LifetimeResult =
     llvm::PointerIntPair<const InitializedEntity *, 3, LifetimeKind>;
@@ -193,6 +197,7 @@ struct IndirectLocalPathEntry {
     VarInit,
     LValToRVal,
     LifetimeBoundCall,
+    LifetimeCapture,
     TemporaryCopy,
     LambdaCaptureInit,
     GslReferenceInit,
@@ -249,7 +254,7 @@ static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
                                                   LocalVisitor Visit);
 
 template <typename T> static bool isRecordWithAttr(QualType Type) {
-  if (auto *RD = Type->getAsCXXRecordDecl())
+  if (auto *RD = Type.getNonReferenceType()->getAsCXXRecordDecl())
     return RD->hasAttr<T>();
   return false;
 }
@@ -1049,6 +1054,7 @@ static SourceRange nextPathEntryRange(const IndirectLocalPath &Path, unsigned I,
     case IndirectLocalPathEntry::AddressOf:
     case IndirectLocalPathEntry::LValToRVal:
     case IndirectLocalPathEntry::LifetimeBoundCall:
+    case IndirectLocalPathEntry::LifetimeCapture:
     case IndirectLocalPathEntry::TemporaryCopy:
     case IndirectLocalPathEntry::GslReferenceInit:
     case IndirectLocalPathEntry::GslPointerInit:
@@ -1082,6 +1088,7 @@ static bool pathOnlyHandlesGslPointer(const IndirectLocalPath &Path) {
     case IndirectLocalPathEntry::VarInit:
     case IndirectLocalPathEntry::AddressOf:
     case IndirectLocalPathEntry::LifetimeBoundCall:
+    case IndirectLocalPathEntry::LifetimeCapture:
       continue;
     case IndirectLocalPathEntry::GslPointerInit:
     case IndirectLocalPathEntry::GslReferenceInit:
@@ -1110,12 +1117,13 @@ static bool shouldRunGSLAssignmentAnalysis(const Sema &SemaRef,
            isAssignmentOperatorLifetimeBound(Entity.AssignmentOperator)));
 }
 
-static void checkExprLifetimeImpl(Sema &SemaRef,
-                                  const InitializedEntity *InitEntity,
-                                  const InitializedEntity *ExtendingEntity,
-                                  LifetimeKind LK,
-                                  const AssignedEntity *AEntity, Expr *Init) {
+static void
+checkExprLifetimeImpl(Sema &SemaRef, const InitializedEntity *InitEntity,
+                      const InitializedEntity *ExtendingEntity, LifetimeKind LK,
+                      const AssignedEntity *AEntity,
+                      const CapturingEntity *CapEntity, Expr *Init) {
   assert((AEntity && LK == LK_Assignment) ||
+         (CapEntity && LK == LK_LifetimeCapture) ||
          (InitEntity && LK != LK_Assignment));
   // If this entity doesn't have an interesting lifetime, don't bother looking
   // for temporaries within its initializer.
@@ -1199,6 +1207,23 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
       break;
     }
 
+    case LK_LifetimeCapture: {
+      // The captured entity has lifetime beyond the full-expression,
+      // and the capturing entity does too, so don't warn.
+      if (!MTE)
+        return false;
+      assert(shouldLifetimeExtendThroughPath(Path) ==
+                 PathLifetimeKind::NoExtend &&
+             "No lifetime extension in function calls");
+      if (CapEntity->Entity)
+        SemaRef.Diag(DiagLoc, diag::warn_dangling_reference_captured)
+            << CapEntity->Entity << DiagRange;
+      else
+        SemaRef.Diag(DiagLoc, diag::warn_dangling_reference_captured_by_unknown)
+            << DiagRange;
+      return false;
+    }
+
     case LK_Assignment: {
       if (!MTE || pathContainsInit(Path))
         return false;
@@ -1359,6 +1384,7 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         break;
 
       case IndirectLocalPathEntry::LifetimeBoundCall:
+      case IndirectLocalPathEntry::LifetimeCapture:
       case IndirectLocalPathEntry::TemporaryCopy:
       case IndirectLocalPathEntry::GslPointerInit:
       case IndirectLocalPathEntry::GslReferenceInit:
@@ -1411,7 +1437,7 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
     // warnings or errors on inner temporaries within this one's initializer.
     return false;
   };
-
+  bool HasReferenceBinding = Init->isGLValue();
   llvm::SmallVector<IndirectLocalPathEntry, 8> Path;
   if (LK == LK_Assignment &&
       shouldRunGSLAssignmentAnalysis(SemaRef, *AEntity)) {
@@ -1420,9 +1446,18 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
              ? IndirectLocalPathEntry::LifetimeBoundCall
              : IndirectLocalPathEntry::GslPointerAssignment,
          Init});
+  } else if (LK == LK_LifetimeCapture) {
+    Path.push_back({IndirectLocalPathEntry::LifetimeCapture, Init});
+    if (isRecordWithAttr<PointerAttr>(Init->getType()))
+      HasReferenceBinding = false;
+    // Skip the top MTE if it is a temporary object of the pointer-like type
+    // itself.
+    if (auto *MTE = dyn_cast<MaterializeTemporaryExpr>(Init);
+        MTE && isPointerLikeType(Init->getType()))
+      Init = MTE->getSubExpr();
   }
 
-  if (Init->isGLValue())
+  if (HasReferenceBinding)
     visitLocalsRetainedByReferenceBinding(Path, Init, RK_ReferenceBinding,
                                           TemporaryVisitor);
   else
@@ -1438,13 +1473,13 @@ void checkExprLifetime(Sema &SemaRef, const InitializedEntity &Entity,
   LifetimeKind LK = LTResult.getInt();
   const InitializedEntity *ExtendingEntity = LTResult.getPointer();
   checkExprLifetimeImpl(SemaRef, &Entity, ExtendingEntity, LK,
-                        /*AEntity*/ nullptr, Init);
+                        /*AEntity=*/nullptr, /*CapEntity=*/nullptr, Init);
 }
 
 void checkExprLifetimeMustTailArg(Sema &SemaRef,
                                   const InitializedEntity &Entity, Expr *Init) {
   checkExprLifetimeImpl(SemaRef, &Entity, nullptr, LK_MustTail,
-                        /*AEntity*/ nullptr, Init);
+                        /*AEntity=*/nullptr, /*CapEntity=*/nullptr, Init);
 }
 
 void checkExprLifetime(Sema &SemaRef, const AssignedEntity &Entity,
@@ -1460,7 +1495,15 @@ void checkExprLifetime(Sema &SemaRef, const AssignedEntity &Entity,
 
   checkExprLifetimeImpl(SemaRef, /*InitEntity=*/nullptr,
                         /*ExtendingEntity=*/nullptr, LK_Assignment, &Entity,
-                        Init);
+                        /*CapEntity=*/nullptr, Init);
+}
+
+void checkExprLifetime(Sema &SemaRef, const CapturingEntity &Entity,
+                       Expr *Init) {
+  return checkExprLifetimeImpl(SemaRef, /*InitEntity=*/nullptr,
+                               /*ExtendingEntity=*/nullptr, LK_LifetimeCapture,
+                               /*AEntity=*/nullptr,
+                               /*CapEntity=*/&Entity, Init);
 }
 
 } // namespace clang::sema

clang/lib/Sema/CheckExprLifetime.h

@@ -25,6 +25,18 @@ struct AssignedEntity {
   CXXMethodDecl *AssignmentOperator = nullptr;
 };
 
+struct CapturingEntity {
+  // In an function call involving a lifetime capture, this would be the
+  // argument capturing the lifetime of another argument.
+  //    void addToSet(std::string_view sv [[clang::lifetime_capture_by(setsv)]],
+  //                  set<std::string_view>& setsv);
+  //    set<std::string_view> setsv;
+  //    addToSet(std::string(), setsv); // Here 'setsv' is the 'Entity'.
+  //
+  // This is 'nullptr' when the capturing entity is 'global' or 'unknown'.
+  Expr *Entity = nullptr;
+};
+
 /// Check that the lifetime of the given expr (and its subobjects) is
 /// sufficient for initializing the entity, and perform lifetime extension
 /// (when permitted) if not.
@@ -35,6 +47,9 @@ void checkExprLifetime(Sema &SemaRef, const InitializedEntity &Entity,
 /// sufficient for assigning to the entity.
 void checkExprLifetime(Sema &SemaRef, const AssignedEntity &Entity, Expr *Init);
 
+void checkExprLifetime(Sema &SemaRef, const CapturingEntity &Entity,
+                       Expr *Init);
+
 /// Check that the lifetime of the given expr (and its subobjects) is
 /// sufficient, assuming that it is passed as an argument to a musttail
 /// function.

clang/lib/Sema/SemaChecking.cpp

@@ -11,6 +11,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "CheckExprLifetime.h"
 #include "clang/AST/APValue.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Attr.h"
@@ -3229,6 +3230,52 @@ void Sema::CheckArgAlignment(SourceLocation Loc, NamedDecl *FDecl,
         << ParamName << (FDecl != nullptr) << FDecl;
 }
 
+void Sema::checkLifetimeCaptureBy(FunctionDecl *FD, bool IsMemberFunction,
+                                  const Expr *ThisArg,
+                                  ArrayRef<const Expr *> Args) {
+  auto GetArgAt = [&](int Idx) -> Expr * {
+    if (Idx == LifetimeCaptureByAttr::GLOBAL ||
+        Idx == LifetimeCaptureByAttr::UNKNOWN)
+      return nullptr;
+    if (IsMemberFunction && Idx == 0)
+      return const_cast<Expr *>(ThisArg);
+    return const_cast<Expr *>(Args[Idx - int(IsMemberFunction)]);
+  };
+  for (unsigned I = 0; I < FD->getNumParams(); ++I) {
+    auto *CapturedByAttr =
+        FD->getParamDecl(I)->getAttr<LifetimeCaptureByAttr>();
+    if (!CapturedByAttr)
+      continue;
+    for (int CapturingParamIdx : CapturedByAttr->params()) {
+      Expr *Capturing = GetArgAt(CapturingParamIdx);
+      Expr *Captured = GetArgAt(I + IsMemberFunction);
+      CapturingEntity CE{Capturing};
+      // Ensure that 'Captured' outlives the 'Capturing' entity.
+      checkExprLifetime(*this, CE, Captured);
+    }
+  }
+  // Check when the 'this' object is captured.
+  if (IsMemberFunction) {
+    TypeSourceInfo *TSI = FD->getTypeSourceInfo();
+    if (!TSI)
+      return;
+    AttributedTypeLoc ATL;
+    for (TypeLoc TL = TSI->getTypeLoc();
+         (ATL = TL.getAsAdjusted<AttributedTypeLoc>());
+         TL = ATL.getModifiedLoc()) {
+      auto *CapturedByAttr = ATL.getAttrAs<LifetimeCaptureByAttr>();
+      if (!CapturedByAttr)
+        continue;
+      Expr *Captured = GetArgAt(0);
+      for (int CapturingParamIdx : CapturedByAttr->params()) {
+        Expr *Capturing = GetArgAt(CapturingParamIdx);
+        CapturingEntity CE{Capturing};
+        checkExprLifetime(*this, CE, Captured);
+      }
+    }
+  }
+}
+
 void Sema::checkCall(NamedDecl *FDecl, const FunctionProtoType *Proto,
                      const Expr *ThisArg, ArrayRef<const Expr *> Args,
                      bool IsMemberFunction, SourceLocation Loc,
@@ -3269,7 +3316,8 @@ void Sema::checkCall(NamedDecl *FDecl, const FunctionProtoType *Proto,
       }
     }
   }
-
+  if (FD)
+    checkLifetimeCaptureBy(FD, IsMemberFunction, ThisArg, Args);
   if (FDecl || Proto) {
     CheckNonNullArguments(*this, FDecl, Proto, Args, Loc);