[clang][modules] Add support for merging lifetime-extended temporaries

Summary: Add support for merging lifetime-extended temporaries

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: xbolva00, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D70190

clang/include/clang/AST/DeclCXX.h

@@ -3041,7 +3041,9 @@ public:
 
 /// Implicit declaration of a temporary that was materialized by
 /// a MaterializeTemporaryExpr and lifetime-extended by a declaration
-class LifetimeExtendedTemporaryDecl final : public Decl {
+class LifetimeExtendedTemporaryDecl final
+    : public Decl,
+      public Mergeable<LifetimeExtendedTemporaryDecl> {
   friend class MaterializeTemporaryExpr;
   friend class ASTDeclReader;
 

clang/include/clang/AST/TextNodeDumper.h

@@ -346,6 +346,8 @@ public:
   void VisitObjCPropertyImplDecl(const ObjCPropertyImplDecl *D);
   void VisitBlockDecl(const BlockDecl *D);
   void VisitConceptDecl(const ConceptDecl *D);
+  void
+  VisitLifetimeExtendedTemporaryDecl(const LifetimeExtendedTemporaryDecl *D);
 };
 
 } // namespace clang

clang/include/clang/Serialization/ASTReader.h

@@ -551,6 +551,14 @@ private:
   llvm::DenseMap<Decl*, llvm::SmallVector<NamedDecl*, 2>>
     AnonymousDeclarationsForMerging;
 
+  /// Key used to identify LifetimeExtendedTemporaryDecl for merging,
+  /// containing the lifetime-extending declaration and the mangling number.
+  using LETemporaryKey = std::pair<Decl *, unsigned>;
+
+  /// Map of already deserialiazed temporaries.
+  llvm::DenseMap<LETemporaryKey, LifetimeExtendedTemporaryDecl *>
+      LETemporaryForMerging;
+
   struct FileDeclsInfo {
     ModuleFile *Mod = nullptr;
     ArrayRef<serialization::LocalDeclID> Decls;

clang/lib/AST/TextNodeDumper.cpp

@@ -1338,6 +1338,17 @@ void TextNodeDumper::VisitFunctionDecl(const FunctionDecl *D) {
     OS << " <<<NULL params x " << D->getNumParams() << ">>>";
 }
 
+void TextNodeDumper::VisitLifetimeExtendedTemporaryDecl(
+    const LifetimeExtendedTemporaryDecl *D) {
+  OS << " extended by ";
+  dumpBareDeclRef(D->getExtendingDecl());
+  OS << " mangling ";
+  {
+    ColorScope Color(OS, ShowColors, ValueColor);
+    OS << D->getManglingNumber();
+  }
+}
+
 void TextNodeDumper::VisitFieldDecl(const FieldDecl *D) {
   dumpName(D);
   dumpType(D->getType());

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -424,6 +424,8 @@ namespace clang {
     template<typename T>
     void mergeMergeable(Mergeable<T> *D);
 
+    void mergeMergeable(LifetimeExtendedTemporaryDecl *D);
+
     void mergeTemplatePattern(RedeclarableTemplateDecl *D,
                               RedeclarableTemplateDecl *Existing,
                               DeclID DsID, bool IsKeyDecl);
@@ -2358,6 +2360,7 @@ void ASTDeclReader::VisitLifetimeExtendedTemporaryDecl(
   if (Record.readInt())
     D->Value = new (D->getASTContext()) APValue(Record.readAPValue());
   D->ManglingNumber = Record.readInt();
+  mergeMergeable(D);
 }
 
 std::pair<uint64_t, uint64_t>
@@ -2555,6 +2558,25 @@ static bool allowODRLikeMergeInC(NamedDecl *ND) {
   return false;
 }
 
+/// Attempts to merge LifetimeExtendedTemporaryDecl with
+/// identical class definitions from two different modules.
+void ASTDeclReader::mergeMergeable(LifetimeExtendedTemporaryDecl *D) {
+  // If modules are not available, there is no reason to perform this merge.
+  if (!Reader.getContext().getLangOpts().Modules)
+    return;
+
+  LifetimeExtendedTemporaryDecl *LETDecl = D;
+
+  LifetimeExtendedTemporaryDecl *&LookupResult =
+      Reader.LETemporaryForMerging[std::make_pair(
+          LETDecl->getExtendingDecl(), LETDecl->getManglingNumber())];
+  if (LookupResult)
+    Reader.getContext().setPrimaryMergedDecl(LETDecl,
+                                             LookupResult->getCanonicalDecl());
+  else
+    LookupResult = LETDecl;
+}
+
 /// Attempts to merge the given declaration (D) with another declaration
 /// of the same entity, for the case where the entity is not actually
 /// redeclarable. This happens, for instance, when merging the fields of

clang/test/Modules/Inputs/merge-lifetime-extended-temporary/a.h

@@ -0,0 +1,2 @@
+
+constexpr const int& LETemp = 0;

clang/test/Modules/Inputs/merge-lifetime-extended-temporary/b.h

@@ -0,0 +1,4 @@
+
+#include "a.h"
+
+constexpr const int* PtrTemp1 = &LETemp;

clang/test/Modules/Inputs/merge-lifetime-extended-temporary/c.h

@@ -0,0 +1,4 @@
+
+#include "a.h"
+
+constexpr const int* PtrTemp2 = &LETemp;

clang/test/Modules/Inputs/merge-lifetime-extended-temporary/module.modulemap

@@ -0,0 +1,14 @@
+module "a" {
+  export *
+  header "a.h"
+}
+
+module "b" {
+  export *
+  header "b.h"
+}
+
+module "c" {
+  export *
+  header "c.h"
+}

clang/test/Modules/merge-lifetime-extended-temporary.cpp

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-lifetime-extended-temporary -verify -std=c++11 %s -DORDER=1
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-lifetime-extended-temporary -verify -std=c++11 %s -DORDER=2
+
+// expected-no-diagnostics
+#if ORDER == 1
+#include "c.h"
+#include "b.h"
+#else
+#include "b.h"
+#include "c.h"
+#endif
+
+static_assert(PtrTemp1 == &LETemp, "");
+static_assert(PtrTemp1 == PtrTemp2, "");