3 files changed, 44 insertions, 28 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 5746a102b71..72b61b8e584 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -14579,6 +14579,7 @@ namespace {
 
     // Make sure we redo semantic analysis
     bool AlwaysRebuild() { return true; }
+    bool ReplacingOriginal() { return true; }
 
     // We need to special-case DeclRefExprs referring to FieldDecls which
     // are not part of a member pointer formation; normal TreeTransforming
@@ -14605,10 +14606,11 @@ namespace {
       return BaseTransform::TransformUnaryOperator(E);
     }
 
-    ExprResult TransformLambdaExpr(LambdaExpr *E) {
-      // Lambdas never need to be transformed.
-      return E;
-    }
+    // The body of a lambda-expression is in a separate expression evaluation
+    // context so never needs to be transformed.
+    // FIXME: Ideally we wouldn't transform the closure type either, and would
+    // just recreate the capture expressions and lambda expression.
+    StmtResult TransformLambdaBody(Stmt *Body) { return Body; }
   };
 }
 
@@ -14715,13 +14717,6 @@ void Sema::PopExpressionEvaluationContext() {
 
       for (const auto *L : Rec.Lambdas)
         Diag(L->getBeginLoc(), D);
-    } else {
-      // Mark the capture expressions odr-used. This was deferred
-      // during lambda expression creation.
-      for (auto *Lambda : Rec.Lambdas) {
-        for (auto *C : Lambda->capture_inits())
-          MarkDeclarationsReferencedInExpr(C);
-      }
     }
   }
 
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index 4b832f56530..ccc8f6f42a5 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -367,12 +367,11 @@ Sema::ExpressionEvaluationContextRecord::getMangleNumberingContext(
   return *MangleNumbering;
 }
 
-CXXMethodDecl *Sema::startLambdaDefinition(CXXRecordDecl *Class,
-                                           SourceRange IntroducerRange,
-                                           TypeSourceInfo *MethodTypeInfo,
-                                           SourceLocation EndLoc,
-                                           ArrayRef<ParmVarDecl *> Params,
-                                           const bool IsConstexprSpecified) {
+CXXMethodDecl *Sema::startLambdaDefinition(
+    CXXRecordDecl *Class, SourceRange IntroducerRange,
+    TypeSourceInfo *MethodTypeInfo, SourceLocation EndLoc,
+    ArrayRef<ParmVarDecl *> Params, const bool IsConstexprSpecified,
+    Optional<std::pair<unsigned, Decl *>> Mangling) {
   QualType MethodType = MethodTypeInfo->getType();
   TemplateParameterList *TemplateParams =
             getGenericLambdaTemplateParameterList(getCurLambda(), *this);
@@ -438,12 +437,16 @@ CXXMethodDecl *Sema::startLambdaDefinition(CXXRecordDecl *Class,
       P->setOwningFunction(Method);
   }
 
-  Decl *ManglingContextDecl;
-  if (MangleNumberingContext *MCtx =
-          getCurrentMangleNumberContext(Class->getDeclContext(),
-                                        ManglingContextDecl)) {
-    unsigned ManglingNumber = MCtx->getManglingNumber(Method);
-    Class->setLambdaMangling(ManglingNumber, ManglingContextDecl);
+  if (Mangling) {
+    Class->setLambdaMangling(Mangling->first, Mangling->second);
+  } else {
+    Decl *ManglingContextDecl;
+    if (MangleNumberingContext *MCtx =
+            getCurrentMangleNumberContext(Class->getDeclContext(),
+                                          ManglingContextDecl)) {
+      unsigned ManglingNumber = MCtx->getManglingNumber(Method);
+      Class->setLambdaMangling(ManglingNumber, ManglingContextDecl);
+    }
   }
 
   return Method;
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 6620885f239..f46193502b6 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -148,6 +148,11 @@ public:
   /// statement node appears at most once in its containing declaration.
   bool AlwaysRebuild() { return SemaRef.ArgumentPackSubstitutionIndex != -1; }
 
+  /// Whether the transformation is forming an expression or statement that
+  /// replaces the original. In this case, we'll reuse mangling numbers from
+  /// existing lambdas.
+  bool ReplacingOriginal() { return false; }
+
   /// Returns the location of the entity being transformed, if that
   /// information was not available elsewhere in the AST.
   ///
@@ -654,6 +659,9 @@ public:
                                           Optional<unsigned> NumExpansions,
                                           bool ExpectParameterPack);
 
+  /// Transform the body of a lambda-expression.
+  StmtResult TransformLambdaBody(Stmt *Body);
+
   QualType TransformReferenceType(TypeLocBuilder &TLB, ReferenceTypeLoc TL);
 
   StmtResult TransformCompoundStmt(CompoundStmt *S, bool IsStmtExpr);
@@ -11197,8 +11205,6 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
 
     auto SubstInitCapture = [&](SourceLocation EllipsisLoc,
                                 Optional<unsigned> NumExpansions) {
-      EnterExpressionEvaluationContext EEEC(
-          getSema(), Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
       ExprResult NewExprInitResult = getDerived().TransformInitializer(
           OldVD->getInit(), OldVD->getInitStyle() == VarDecl::CallInit);
 
@@ -11289,19 +11295,25 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
   LSI->GLTemplateParameterList = TPL;
 
   // Create the local class that will describe the lambda.
+  CXXRecordDecl *OldClass = E->getLambdaClass();
   CXXRecordDecl *Class
     = getSema().createLambdaClosureType(E->getIntroducerRange(),
                                         NewCallOpTSI,
                                         /*KnownDependent=*/false,
                                         E->getCaptureDefault());
-  getDerived().transformedLocalDecl(E->getLambdaClass(), {Class});
+  getDerived().transformedLocalDecl(OldClass, {Class});
+
+  Optional<std::pair<unsigned, Decl*>> Mangling;
+  if (getDerived().ReplacingOriginal())
+    Mangling = std::make_pair(OldClass->getLambdaManglingNumber(),
+                              OldClass->getLambdaContextDecl());
 
   // Build the call operator.
   CXXMethodDecl *NewCallOperator = getSema().startLambdaDefinition(
       Class, E->getIntroducerRange(), NewCallOpTSI,
       E->getCallOperator()->getEndLoc(),
       NewCallOpTSI->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams(),
-      E->getCallOperator()->isConstexpr());
+      E->getCallOperator()->isConstexpr(), Mangling);
 
   LSI->CallOperator = NewCallOperator;
 
@@ -11465,7 +11477,7 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
 
   // Instantiate the body of the lambda expression.
   StmtResult Body =
-      Invalid ? StmtError() : getDerived().TransformStmt(E->getBody());
+      Invalid ? StmtError() : getDerived().TransformLambdaBody(E->getBody());
 
   // ActOnLambda* will pop the function scope for us.
   FuncScopeCleanup.disable();
@@ -11490,6 +11502,12 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
 }
 
 template<typename Derived>
+StmtResult
+TreeTransform<Derived>::TransformLambdaBody(Stmt *S) {
+  return TransformStmt(S);
+}
+
+template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformCXXUnresolvedConstructExpr(
                                                   CXXUnresolvedConstructExpr *E) {