[ODRHash] Support ODR violation detection in functions.

Extend the hashing to functions, which allows detection of function definition
mismatches across modules.  This is a re-commit of r320230.

llvm-svn: 321395

clang/include/clang/AST/Decl.h

@@ -1759,6 +1759,11 @@ protected:
   unsigned IsCopyDeductionCandidate : 1;
 
 private:
+
+  /// Store the ODRHash after first calculation.
+  unsigned HasODRHash : 1;
+  unsigned ODRHash;
+
   /// \brief End part of this FunctionDecl's source range.
   ///
   /// We could compute the full range in getSourceRange(). However, when we're
@@ -1841,8 +1846,9 @@ protected:
         IsExplicitlyDefaulted(false), HasImplicitReturnZero(false),
         IsLateTemplateParsed(false), IsConstexpr(isConstexprSpecified),
         InstantiationIsPending(false), UsesSEHTry(false), HasSkippedBody(false),
-        WillHaveBody(false), IsCopyDeductionCandidate(false),
-        EndRangeLoc(NameInfo.getEndLoc()), DNLoc(NameInfo.getInfo()) {}
+        WillHaveBody(false), IsCopyDeductionCandidate(false), HasODRHash(false),
+        ODRHash(0), EndRangeLoc(NameInfo.getEndLoc()),
+        DNLoc(NameInfo.getInfo()) {}
 
   using redeclarable_base = Redeclarable<FunctionDecl>;
 
@@ -2439,6 +2445,10 @@ public:
   /// returns 0.
   unsigned getMemoryFunctionKind() const;
 
+  /// \brief Returns ODRHash of the function.  This value is calculated and
+  /// stored on first call, then the stored value returned on the other calls.
+  unsigned getODRHash();
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) {

clang/include/clang/AST/ODRHash.h

@@ -53,6 +53,10 @@ public:
   // more information than the AddDecl class.
   void AddCXXRecordDecl(const CXXRecordDecl *Record);
 
+  // Use this for ODR checking functions between modules.  This method compares
+  // more information than the AddDecl class.
+  void AddFunctionDecl(const FunctionDecl *Function);
+
   // Process SubDecls of the main Decl.  This method calls the DeclVisitor
   // while AddDecl does not.
   void AddSubDecl(const Decl *D);

clang/include/clang/Basic/DiagnosticSerializationKinds.td

@@ -270,6 +270,29 @@ def note_module_odr_violation_mismatch_decl_diff : Note<"but in '%0' found "
   "friend function %2|"
   "}1">;
 
+def err_module_odr_violation_function : Error<
+  "%q0 has different definitions in different modules; "
+  "%select{definition in module '%2'|defined here}1 "
+  "first difference is "
+  "%select{"
+  "return type is %4|"
+  "%ordinal4 parameter with name %5|"
+  "%ordinal4 parameter with type %5%select{| decayed from %7}6|"
+  "%ordinal4 parameter with%select{out|}5 a default argument|"
+  "%ordinal4 parameter with a default argument|"
+  "function body"
+  "}3">;
+
+def note_module_odr_violation_function : Note<"but in '%0' found "
+  "%select{"
+  "different return type %2|"
+  "%ordinal2 parameter with name %3|"
+  "%ordinal2 parameter with type %3%select{| decayed from %5}4|"
+  "%ordinal2 parameter with%select{out|}3 a default argument|"
+  "%ordinal2 parameter with a different default argument|"
+  "a different body"
+  "}1">;
+
 def err_module_odr_violation_mismatch_decl_unknown : Error<
   "%q0 %select{with definition in module '%2'|defined here}1 has different "
   "definitions in different modules; first difference is this "

clang/include/clang/Serialization/ASTReader.h

@@ -1092,6 +1092,10 @@ private:
   llvm::SmallDenseMap<CXXRecordDecl *, llvm::SmallVector<DataPointers, 2>, 2>
       PendingOdrMergeFailures;
 
+  /// \brief Function definitions in which we found an ODR violation.
+  llvm::SmallDenseMap<FunctionDecl *, llvm::SmallVector<FunctionDecl *, 2>, 2>
+      PendingFunctionOdrMergeFailures;
+
   /// \brief DeclContexts in which we have diagnosed an ODR violation.
   llvm::SmallPtrSet<DeclContext*, 2> DiagnosedOdrMergeFailures;
 

clang/lib/AST/Decl.cpp

@@ -26,6 +26,7 @@
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/ExternalASTSource.h"
+#include "clang/AST/ODRHash.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/Redeclarable.h"
 #include "clang/AST/Stmt.h"
@@ -3604,6 +3605,25 @@ unsigned FunctionDecl::getMemoryFunctionKind() const {
   return 0;
 }
 
+unsigned FunctionDecl::getODRHash() {
+  if (HasODRHash)
+    return ODRHash;
+
+  if (FunctionDecl *Definition = getDefinition()) {
+    if (Definition != this) {
+      HasODRHash = true;
+      ODRHash = Definition->getODRHash();
+      return ODRHash;
+    }
+  }
+
+  class ODRHash Hash;
+  Hash.AddFunctionDecl(this);
+  HasODRHash = true;
+  ODRHash = Hash.CalculateHash();
+  return ODRHash;
+}
+
 //===----------------------------------------------------------------------===//
 // FieldDecl Implementation
 //===----------------------------------------------------------------------===//

clang/lib/AST/ODRHash.cpp

@@ -466,6 +466,36 @@ void ODRHash::AddCXXRecordDecl(const CXXRecordDecl *Record) {
   }
 }
 
+void ODRHash::AddFunctionDecl(const FunctionDecl *Function) {
+  assert(Function && "Expecting non-null pointer.");
+
+  // Skip hashing these kinds of function.
+  if (Function->isImplicit()) return;
+  if (Function->isDefaulted()) return;
+  if (Function->isDeleted()) return;
+  if (!Function->hasBody()) return;
+  if (!Function->getBody()) return;
+
+  // Skip functions that are specializations or in specialization context.
+  const DeclContext *DC = Function;
+  while (DC) {
+    if (isa<ClassTemplateSpecializationDecl>(DC)) return;
+    if (auto *F = dyn_cast<FunctionDecl>(DC))
+      if (F->isFunctionTemplateSpecialization()) return;
+    DC = DC->getParent();
+  }
+
+  AddDecl(Function);
+
+  AddQualType(Function->getReturnType());
+
+  ID.AddInteger(Function->param_size());
+  for (auto Param : Function->parameters())
+    AddSubDecl(Param);
+
+  AddStmt(Function->getBody());
+}
+
 void ODRHash::AddDecl(const Decl *D) {
   assert(D && "Expecting non-null pointer.");
   D = D->getCanonicalDecl();

clang/lib/Serialization/ASTReader.cpp

@@ -9235,8 +9235,16 @@ void ASTReader::finishPendingActions() {
       const FunctionDecl *Defn = nullptr;
       if (!getContext().getLangOpts().Modules || !FD->hasBody(Defn)) {
         FD->setLazyBody(PB->second);
-      } else
-        mergeDefinitionVisibility(const_cast<FunctionDecl*>(Defn), FD);
+      } else {
+        auto *NonConstDefn = const_cast<FunctionDecl*>(Defn);
+        mergeDefinitionVisibility(NonConstDefn, FD);
+
+        if (!FD->isLateTemplateParsed() &&
+            !NonConstDefn->isLateTemplateParsed() &&
+            FD->getODRHash() != NonConstDefn->getODRHash()) {
+          PendingFunctionOdrMergeFailures[FD].push_back(NonConstDefn);
+        }
+      }
       continue;
     }
 
@@ -9253,7 +9261,8 @@ void ASTReader::finishPendingActions() {
 }
 
 void ASTReader::diagnoseOdrViolations() {
-  if (PendingOdrMergeFailures.empty() && PendingOdrMergeChecks.empty())
+  if (PendingOdrMergeFailures.empty() && PendingOdrMergeChecks.empty() &&
+      PendingFunctionOdrMergeFailures.empty())
     return;
 
   // Trigger the import of the full definition of each class that had any
@@ -9275,6 +9284,20 @@ void ASTReader::diagnoseOdrViolations() {
     }
   }
 
+  // Trigger the import of functions.
+  auto FunctionOdrMergeFailures = std::move(PendingFunctionOdrMergeFailures);
+  PendingFunctionOdrMergeFailures.clear();
+  for (auto &Merge : FunctionOdrMergeFailures) {
+    Merge.first->buildLookup();
+    Merge.first->decls_begin();
+    Merge.first->getBody();
+    for (auto &FD : Merge.second) {
+      FD->buildLookup();
+      FD->decls_begin();
+      FD->getBody();
+    }
+  }
+
   // For each declaration from a merged context, check that the canonical
   // definition of that context also contains a declaration of the same
   // entity.
@@ -9357,13 +9380,35 @@ void ASTReader::diagnoseOdrViolations() {
     }
   }
 
-  if (OdrMergeFailures.empty())
+  if (OdrMergeFailures.empty() && FunctionOdrMergeFailures.empty())
     return;
 
   // Ensure we don't accidentally recursively enter deserialization while
   // we're producing our diagnostics.
   Deserializing RecursionGuard(this);
 
+  // Common code for hashing helpers.
+  ODRHash Hash;
+  auto ComputeQualTypeODRHash = [&Hash](QualType Ty) {
+    Hash.clear();
+    Hash.AddQualType(Ty);
+    return Hash.CalculateHash();
+  };
+
+  auto ComputeODRHash = [&Hash](const Stmt *S) {
+    assert(S);
+    Hash.clear();
+    Hash.AddStmt(S);
+    return Hash.CalculateHash();
+  };
+
+  auto ComputeSubDeclODRHash = [&Hash](const Decl *D) {
+    assert(D);
+    Hash.clear();
+    Hash.AddSubDecl(D);
+    return Hash.CalculateHash();
+  };
+
   // Issue any pending ODR-failure diagnostics.
   for (auto &Merge : OdrMergeFailures) {
     // If we've already pointed out a specific problem with this class, don't
@@ -9411,13 +9456,6 @@ void ASTReader::diagnoseOdrViolations() {
                  << SecondModule << Range << DiffType;
         };
 
-        ODRHash Hash;
-        auto ComputeQualTypeODRHash = [&Hash](QualType Ty) {
-          Hash.clear();
-          Hash.AddQualType(Ty);
-          return Hash.CalculateHash();
-        };
-
         unsigned FirstNumBases = FirstDD->NumBases;
         unsigned FirstNumVBases = FirstDD->NumVBases;
         unsigned SecondNumBases = SecondDD->NumBases;
@@ -9520,14 +9558,12 @@ void ASTReader::diagnoseOdrViolations() {
       if (FirstTemplate && SecondTemplate) {
         DeclHashes FirstTemplateHashes;
         DeclHashes SecondTemplateHashes;
-        ODRHash Hash;
 
         auto PopulateTemplateParameterHashs =
-            [&Hash](DeclHashes &Hashes, const ClassTemplateDecl *TD) {
+            [&ComputeSubDeclODRHash](DeclHashes &Hashes,
+                                     const ClassTemplateDecl *TD) {
               for (auto *D : TD->getTemplateParameters()->asArray()) {
-                Hash.clear();
-                Hash.AddSubDecl(D);
-                Hashes.emplace_back(D, Hash.CalculateHash());
+                Hashes.emplace_back(D, ComputeSubDeclODRHash(D));
               }
             };
 
@@ -9696,18 +9732,15 @@ void ASTReader::diagnoseOdrViolations() {
 
       DeclHashes FirstHashes;
       DeclHashes SecondHashes;
-      ODRHash Hash;
 
-      auto PopulateHashes = [&Hash, FirstRecord](DeclHashes &Hashes,
-                                                 CXXRecordDecl *Record) {
+      auto PopulateHashes = [&ComputeSubDeclODRHash, FirstRecord](
+                                DeclHashes &Hashes, CXXRecordDecl *Record) {
         for (auto *D : Record->decls()) {
           // Due to decl merging, the first CXXRecordDecl is the parent of
           // Decls in both records.
           if (!ODRHash::isWhitelistedDecl(D, FirstRecord))
             continue;
-          Hash.clear();
-          Hash.AddSubDecl(D);
-          Hashes.emplace_back(D, Hash.CalculateHash());
+          Hashes.emplace_back(D, ComputeSubDeclODRHash(D));
         }
       };
       PopulateHashes(FirstHashes, FirstRecord);
@@ -9901,19 +9934,6 @@ void ASTReader::diagnoseOdrViolations() {
                << SecondModule << Range << DiffType;
       };
 
-      auto ComputeODRHash = [&Hash](const Stmt* S) {
-        assert(S);
-        Hash.clear();
-        Hash.AddStmt(S);
-        return Hash.CalculateHash();
-      };
-
-      auto ComputeQualTypeODRHash = [&Hash](QualType Ty) {
-        Hash.clear();
-        Hash.AddQualType(Ty);
-        return Hash.CalculateHash();
-      };
-
       switch (FirstDiffType) {
       case Other:
       case EndOfClass:
@@ -10488,6 +10508,160 @@ void ASTReader::diagnoseOdrViolations() {
         << Merge.first;
     }
   }
+
+  // Issue ODR failures diagnostics for functions.
+  for (auto &Merge : FunctionOdrMergeFailures) {
+    enum ODRFunctionDifference {
+      ReturnType,
+      ParameterName,
+      ParameterType,
+      ParameterSingleDefaultArgument,
+      ParameterDifferentDefaultArgument,
+      FunctionBody,
+    };
+
+    FunctionDecl *FirstFunction = Merge.first;
+    std::string FirstModule = getOwningModuleNameForDiagnostic(FirstFunction);
+
+    bool Diagnosed = false;
+    for (auto &SecondFunction : Merge.second) {
+
+      if (FirstFunction == SecondFunction)
+        continue;
+
+      std::string SecondModule =
+          getOwningModuleNameForDiagnostic(SecondFunction);
+
+      auto ODRDiagError = [FirstFunction, &FirstModule,
+                           this](SourceLocation Loc, SourceRange Range,
+                                 ODRFunctionDifference DiffType) {
+        return Diag(Loc, diag::err_module_odr_violation_function)
+               << FirstFunction << FirstModule.empty() << FirstModule << Range
+               << DiffType;
+      };
+      auto ODRDiagNote = [&SecondModule, this](SourceLocation Loc,
+                                               SourceRange Range,
+                                               ODRFunctionDifference DiffType) {
+        return Diag(Loc, diag::note_module_odr_violation_function)
+               << SecondModule << Range << DiffType;
+      };
+
+      if (ComputeQualTypeODRHash(FirstFunction->getReturnType()) !=
+          ComputeQualTypeODRHash(SecondFunction->getReturnType())) {
+        ODRDiagError(FirstFunction->getReturnTypeSourceRange().getBegin(),
+                     FirstFunction->getReturnTypeSourceRange(), ReturnType)
+            << FirstFunction->getReturnType();
+        ODRDiagNote(SecondFunction->getReturnTypeSourceRange().getBegin(),
+                    SecondFunction->getReturnTypeSourceRange(), ReturnType)
+            << SecondFunction->getReturnType();
+        Diagnosed = true;
+        break;
+      }
+
+      assert(FirstFunction->param_size() == SecondFunction->param_size() &&
+             "Merged functions with different number of parameters");
+
+      auto ParamSize = FirstFunction->param_size();
+      bool ParameterMismatch = false;
+      for (unsigned I = 0; I < ParamSize; ++I) {
+        auto *FirstParam = FirstFunction->getParamDecl(I);
+        auto *SecondParam = SecondFunction->getParamDecl(I);
+
+        assert(getContext().hasSameType(FirstParam->getType(),
+                                      SecondParam->getType()) &&
+               "Merged function has different parameter types.");
+
+        if (FirstParam->getDeclName() != SecondParam->getDeclName()) {
+          ODRDiagError(FirstParam->getLocation(), FirstParam->getSourceRange(),
+                       ParameterName)
+              << I + 1 << FirstParam->getDeclName();
+          ODRDiagNote(SecondParam->getLocation(), SecondParam->getSourceRange(),
+                      ParameterName)
+              << I + 1 << SecondParam->getDeclName();
+          ParameterMismatch = true;
+          break;
+        };
+
+        QualType FirstParamType = FirstParam->getType();
+        QualType SecondParamType = SecondParam->getType();
+        if (FirstParamType != SecondParamType &&
+            ComputeQualTypeODRHash(FirstParamType) !=
+                ComputeQualTypeODRHash(SecondParamType)) {
+          if (const DecayedType *ParamDecayedType =
+                  FirstParamType->getAs<DecayedType>()) {
+            ODRDiagError(FirstParam->getLocation(),
+                         FirstParam->getSourceRange(), ParameterType)
+                << (I + 1) << FirstParamType << true
+                << ParamDecayedType->getOriginalType();
+          } else {
+            ODRDiagError(FirstParam->getLocation(),
+                         FirstParam->getSourceRange(), ParameterType)
+                << (I + 1) << FirstParamType << false;
+          }
+
+          if (const DecayedType *ParamDecayedType =
+                  SecondParamType->getAs<DecayedType>()) {
+            ODRDiagNote(SecondParam->getLocation(),
+                        SecondParam->getSourceRange(), ParameterType)
+                << (I + 1) << SecondParamType << true
+                << ParamDecayedType->getOriginalType();
+          } else {
+            ODRDiagNote(SecondParam->getLocation(),
+                        SecondParam->getSourceRange(), ParameterType)
+                << (I + 1) << SecondParamType << false;
+          }
+          ParameterMismatch = true;
+          break;
+        }
+
+        const Expr *FirstInit = FirstParam->getInit();
+        const Expr *SecondInit = SecondParam->getInit();
+        if ((FirstInit == nullptr) != (SecondInit == nullptr)) {
+          ODRDiagError(FirstParam->getLocation(), FirstParam->getSourceRange(),
+                       ParameterSingleDefaultArgument)
+              << (I + 1) << (FirstInit == nullptr)
+              << (FirstInit ? FirstInit->getSourceRange() : SourceRange());
+          ODRDiagNote(SecondParam->getLocation(), SecondParam->getSourceRange(),
+                      ParameterSingleDefaultArgument)
+              << (I + 1) << (SecondInit == nullptr)
+              << (SecondInit ? SecondInit->getSourceRange() : SourceRange());
+          ParameterMismatch = true;
+          break;
+        }
+
+        if (FirstInit && SecondInit &&
+            ComputeODRHash(FirstInit) != ComputeODRHash(SecondInit)) {
+          ODRDiagError(FirstParam->getLocation(), FirstParam->getSourceRange(),
+                       ParameterDifferentDefaultArgument)
+              << (I + 1) << FirstInit->getSourceRange();
+          ODRDiagNote(SecondParam->getLocation(), SecondParam->getSourceRange(),
+                      ParameterDifferentDefaultArgument)
+              << (I + 1) << SecondInit->getSourceRange();
+          ParameterMismatch = true;
+          break;
+        }
+
+        assert(ComputeSubDeclODRHash(FirstParam) ==
+                   ComputeSubDeclODRHash(SecondParam) &&
+               "Undiagnosed parameter difference.");
+      }
+
+      if (ParameterMismatch) {
+        Diagnosed = true;
+        break;
+      }
+
+      // If no error has been generated before now, assume the problem is in
+      // the body and generate a message.
+      ODRDiagError(FirstFunction->getLocation(),
+                   FirstFunction->getSourceRange(), FunctionBody);
+      ODRDiagNote(SecondFunction->getLocation(),
+                  SecondFunction->getSourceRange(), FunctionBody);
+      Diagnosed = true;
+      break;
+    }
+    assert(Diagnosed && "Unable to emit ODR diagnostic.");
+  }
 }
 
 void ASTReader::StartedDeserializing() {

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -796,6 +796,9 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
   FD->setCachedLinkage(Linkage(Record.readInt()));
   FD->EndRangeLoc = ReadSourceLocation();
 
+  FD->ODRHash = Record.readInt();
+  FD->HasODRHash = true;
+
   switch ((FunctionDecl::TemplatedKind)Record.readInt()) {
   case FunctionDecl::TK_NonTemplate:
     mergeRedeclarable(FD, Redecl);

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -538,6 +538,8 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
   Record.push_back(D->getLinkageInternal());
   Record.AddSourceLocation(D->getLocEnd());
 
+  Record.push_back(D->getODRHash());
+
   Record.push_back(D->getTemplatedKind());
   switch (D->getTemplatedKind()) {
   case FunctionDecl::TK_NonTemplate:
@@ -2072,6 +2074,7 @@ void ASTWriter::WriteDeclAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // LateParsed
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3)); // Linkage
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // LocEnd
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32)); // ODRHash
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3)); // TemplateKind
   // This Array slurps the rest of the record. Fortunately we want to encode
   // (nearly) all the remaining (variable number of) fields in the same way.

clang/test/Modules/odr_hash.cpp

@@ -557,11 +557,11 @@ S10 s10;
 
 #if defined(FIRST)
 struct S11 {
-  void A(int x) {}
+  void A(int x);
 };
 #elif defined(SECOND)
 struct S11 {
-  void A(int y) {}
+  void A(int y);
 };
 #else
 S11 s11;
@@ -571,11 +571,11 @@ S11 s11;
 
 #if defined(FIRST)
 struct S12 {
-  void A(int x) {}
+  void A(int x);
 };
 #elif defined(SECOND)
 struct S12 {
-  void A(int x = 1) {}
+  void A(int x = 1);
 };
 #else
 S12 s12;
@@ -585,11 +585,11 @@ S12 s12;
 
 #if defined(FIRST)
 struct S13 {
-  void A(int x = 1 + 0) {}
+  void A(int x = 1 + 0);
 };
 #elif defined(SECOND)
 struct S13 {
-  void A(int x = 1) {}
+  void A(int x = 1);
 };
 #else
 S13 s13;
@@ -599,11 +599,11 @@ S13 s13;
 
 #if defined(FIRST)
 struct S14 {
-  void A(int x[2]) {}
+  void A(int x[2]);
 };
 #elif defined(SECOND)
 struct S14 {
-  void A(int x[3]) {}
+  void A(int x[3]);
 };
 #else
 S14 s14;
@@ -2751,14 +2751,14 @@ namespace DefaultArguments {
 template <typename T>
 struct S {
   struct R {
-    void foo(T x = 0) {}
+    void foo(T x = 0);
   };
 };
 #elif defined(SECOND)
 template <typename T>
 struct S {
   struct R {
-    void foo(T x = 1) {}
+    void foo(T x = 1);
   };
 };
 #else
@@ -2771,13 +2771,13 @@ void run() {
 
 #if defined(FIRST)
 template <typename alpha> struct Bravo {
-  void charlie(bool delta = false) {}
+  void charlie(bool delta = false);
 };
 typedef Bravo<char> echo;
 echo foxtrot;
 #elif defined(SECOND)
 template <typename alpha> struct Bravo {
-  void charlie(bool delta = (false)) {}
+  void charlie(bool delta = (false));
 };
 typedef Bravo<char> echo;
 echo foxtrot;
@@ -2788,6 +2788,142 @@ Bravo<char> golf;
 #endif
 }  // namespace DefaultArguments
 
+namespace FunctionDecl {
+#if defined(FIRST)
+struct S1 {};
+S1 s1a;
+#elif defined(SECOND)
+struct S1 {};
+#else
+S1 s1;
+#endif
+
+#if defined(FIRST)
+struct S2 {
+  S2() = default;
+};
+S2 s2a = S2();
+#elif defined(SECOND)
+struct S2 {
+  S2() = default;
+};
+#else
+S2 s2;
+#endif
+
+#if defined(FIRST)
+struct S3 {
+  S3() = delete;
+};
+S3* s3c;
+#elif defined(SECOND)
+struct S3 {
+  S3() = delete;
+};
+#else
+S3* s3;
+#endif
+
+#if defined(FIRST) || defined(SECOND)
+int F1(int x, float y = 2.7) { return 1; }
+#else
+int I1 = F1(1);
+#endif
+
+#if defined(FIRST)
+int F2() { return 1; }
+#elif defined(SECOND)
+double F2() { return 1; }
+#else
+int I2 = F2();
+// expected-error@-1 {{call to 'F2' is ambiguous}}
+// expected-note@first.h:* {{candidate function}}
+// expected-note@second.h:* {{candidate function}}
+#endif
+
+#if defined(FIRST)
+int F3(float) { return 1; }
+#elif defined(SECOND)
+int F3(double) { return 1; }
+#else
+int I3 = F3(1);
+// expected-error@-1 {{call to 'F3' is ambiguous}}
+// expected-note@first.h:* {{candidate function}}
+// expected-note@second.h:* {{candidate function}}
+#endif
+
+#if defined(FIRST)
+int F4(int x) { return 1; }
+#elif defined(SECOND)
+int F4(int y) { return 1; }
+#else
+int I4 = F4(1);
+// expected-error@second.h:* {{'FunctionDecl::F4' has different definitions in different modules; definition in module 'SecondModule' first difference is 1st parameter with name 'y'}}
+// expected-note@first.h:* {{but in 'FirstModule' found 1st parameter with name 'x'}}
+#endif
+
+#if defined(FIRST)
+int F5(int x) { return 1; }
+#elif defined(SECOND)
+int F5(int x = 1) { return 1; }
+#else
+int I5 = F6(1);
+// expected-error@second.h:* {{'FunctionDecl::F5' has different definitions in different modules; definition in module 'SecondModule' first difference is 1st parameter without a default argument}}
+// expected-note@first.h:* {{but in 'FirstModule' found 1st parameter with a default argument}}
+#endif
+
+#if defined(FIRST)
+int F6(int x = 2) { return 1; }
+#elif defined(SECOND)
+int F6(int x = 1) { return 1; }
+#else
+int I6 = F6(1);
+// expected-error@second.h:* {{'FunctionDecl::F6' has different definitions in different modules; definition in module 'SecondModule' first difference is 1st parameter with a default argument}}
+// expected-note@first.h:* {{but in 'FirstModule' found 1st parameter with a different default argument}}
+#endif
+
+using I = int;
+#if defined(FIRST)
+I F7() { return 0; }
+#elif defined(SECOND)
+int F7() { return 0; }
+#else
+int I7 = F7();
+// expected-error@second.h:* {{'FunctionDecl::F7' has different definitions in different modules; definition in module 'SecondModule' first difference is return type is 'int'}}
+// expected-note@first.h:* {{but in 'FirstModule' found different return type 'FunctionDecl::I' (aka 'int')}}
+#endif
+
+#if defined(FIRST)
+int F8(int) { return 0; }
+#elif defined(SECOND)
+int F8(I) { return 0; }
+#else
+int I8 = F8(1);
+// expected-error@second.h:* {{'FunctionDecl::F8' has different definitions in different modules; definition in module 'SecondModule' first difference is 1st parameter with type 'FunctionDecl::I' (aka 'int')}}
+// expected-note@first.h:* {{but in 'FirstModule' found 1st parameter with type 'int'}}
+#endif
+
+#if defined(FIRST)
+int F9(int[1]) { return 0; }
+#elif defined(SECOND)
+int F9(int[2]) { return 0; }
+#else
+int I9 = F9(nullptr);
+// expected-error@second.h:* {{'FunctionDecl::F9' has different definitions in different modules; definition in module 'SecondModule' first difference is 1st parameter with type 'int *' decayed from 'int [2]'}}
+// expected-note@first.h:* {{but in 'FirstModule' found 1st parameter with type 'int *' decayed from 'int [1]'}}
+#endif
+
+#if defined(FIRST)
+int F10() { return 1; }
+#elif defined(SECOND)
+int F10() { return 2; }
+#else
+int I10 = F10();
+#endif
+// expected-error@second.h:* {{'FunctionDecl::F10' has different definitions in different modules; definition in module 'SecondModule' first difference is function body}}
+// expected-note@first.h:* {{but in 'FirstModule' found a different body}}
+}  // namespace FunctionDecl
+
 // Keep macros contained to one file.
 #ifdef FIRST
 #undef FIRST