Clean up handling of function redeclarations

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@50021 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 104 insertions, 10 deletions

diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 6ebaac569f..11e6bcfb0f 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -403,6 +403,18 @@ const char *NamedDecl::getName() const {
 FunctionDecl::~FunctionDecl() {
   delete[] ParamInfo;
   delete Body;
+  delete PreviousDeclaration;
+}
+
+Stmt *FunctionDecl::getBody(const FunctionDecl *&Definition) const {
+  for (const FunctionDecl *FD = this; FD != 0; FD = FD->PreviousDeclaration) {
+    if (FD->Body) {
+      Definition = FD;
+      return FD->Body;
+    }
+  }
+
+  return 0;
 }
 
 unsigned FunctionDecl::getNumParams() const {
@@ -436,6 +448,71 @@ unsigned FunctionDecl::getMinRequiredArguments() const {
   return NumRequiredArgs;
 }
 
+/// AddRedeclaration - Specifies that this function declaration has been
+/// redeclared by the function declaration FD. FD must be a
+/// redeclaration of this based on the semantics of the language being
+/// translated ("compatible" function types in C, same signatures in
+/// C++). 
+void FunctionDecl::AddRedeclaration(FunctionDecl *FD) {
+  assert(FD->PreviousDeclaration == 0 && 
+         "Redeclaration already has a previous declaration!");
+
+  // Insert FD into the list of previous declarations of this
+  // function.
+  FD->PreviousDeclaration = this->PreviousDeclaration;
+  this->PreviousDeclaration = FD;
+
+  // Swap the contents of this function declaration and FD. This
+  // effectively transforms the original declaration into the most
+  // recent declaration, so that all references to this declaration
+  // remain valid (and have information from *all* declarations),
+  // while retaining all of the information about previous
+  // declarations as well.
+
+  // Swap parameters, so that the most recent parameter names and
+  // exact types (e.g., enum vs int) show up in the original
+  // declaration.
+  ParmVarDecl **thisParamInfo = this->ParamInfo;
+  this->ParamInfo = FD->ParamInfo;
+  FD->ParamInfo = thisParamInfo;
+  
+  // Swap the function body: all declarations share the same function
+  // body, but we keep track of who actually defined that function
+  // body by keeping the pointer to the body stored in that node.
+  Stmt *thisBody = this->Body;
+  this->Body = FD->Body;
+  FD->Body = thisBody;
+
+  // Swap type information: this is important because in C, later
+  // declarations can provide slightly different types (enum vs. int,
+  // for example).
+  QualType thisType = this->getType();
+  this->setType(FD->getType());
+  FD->setType(thisType);
+
+  // Swap location information: this allows us to produce diagnostics
+  // later on that reference the most recent declaration (which has
+  // the most information!) while retaining the location of previous
+  // declarations (good for "redefinition" diagnostics).
+  SourceLocation thisLocation = this->getLocation();
+  this->setLocation(FD->getLocation());
+  FD->setLocation(thisLocation);
+  
+  // Swap attributes. FD will have the union of the attributes from
+  // all previous declarations.
+  if (DeclAttrs) {
+    Attr *thisAttr = (*DeclAttrs)[this];
+    (*DeclAttrs)[this] = (*DeclAttrs)[FD];
+    (*DeclAttrs)[FD] = thisAttr;
+  }
+
+  // If any declaration is inline, the function is inline.
+  this->IsInline |= FD->IsInline;
+
+  // FIXME: Is this the right way to handle storage specifiers?
+  if (FD->SClass) this->SClass = FD->SClass;
+}
+
 //===----------------------------------------------------------------------===//
 // RecordDecl Implementation
 //===----------------------------------------------------------------------===//
diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index 6d6a26d95d..e70da932f6 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -268,7 +268,8 @@ private:
   TypedefDecl *ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
                                 ScopedDecl *LastDecl);
   TypedefDecl *MergeTypeDefDecl(TypedefDecl *New, Decl *Old);
-  FunctionDecl *MergeFunctionDecl(FunctionDecl *New, Decl *Old);
+  FunctionDecl *MergeFunctionDecl(FunctionDecl *New, Decl *Old, 
+                                  bool &Redeclaration);
   VarDecl *MergeVarDecl(VarDecl *New, Decl *Old);
   FunctionDecl *MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old);
 
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index eec8ce5d0a..415908a30b 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -256,8 +256,10 @@ static void MergeAttributes(Decl *New, Decl *Old) {
 /// declarator D which has the same name and scope as a previous
 /// declaration 'Old'.  Figure out how to resolve this situation,
 /// merging decls or emitting diagnostics as appropriate.
-///
-FunctionDecl *Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD) {
+/// Redeclaration will be set true if thisNew is a redeclaration OldD.
+FunctionDecl *
+Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD, bool &Redeclaration) {
+  Redeclaration = false;
   // Verify the old decl was also a function.
   FunctionDecl *Old = dyn_cast<FunctionDecl>(OldD);
   if (!Old) {
@@ -267,28 +269,31 @@ FunctionDecl *Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD) {
     return New;
   }
   
-  MergeAttributes(New, Old);
-
   QualType OldQType = Context.getCanonicalType(Old->getType());
   QualType NewQType = Context.getCanonicalType(New->getType());
   
   // C++ [dcl.fct]p3:
   //   All declarations for a function shall agree exactly in both the
   //   return type and the parameter-type-list.
-  if (getLangOptions().CPlusPlus && OldQType == NewQType)
+  if (getLangOptions().CPlusPlus && OldQType == NewQType) {
+    MergeAttributes(New, Old);
+    Redeclaration = true;
     return MergeCXXFunctionDecl(New, Old);
+  }
 
   // C: Function types need to be compatible, not identical. This handles
   // duplicate function decls like "void f(int); void f(enum X);" properly.
   if (!getLangOptions().CPlusPlus &&
       Context.functionTypesAreCompatible(OldQType, NewQType)) {
+    MergeAttributes(New, Old);
+    Redeclaration = true;
     return New;
   }
 
   // A function that has already been declared has been redeclared or defined
   // with a different type- show appropriate diagnostic
   diag::kind PrevDiag;
-  if (Old->getBody())
+  if (Old->isThisDeclarationADefinition())
     PrevDiag = diag::err_previous_definition;
   else if (Old->isImplicit())
     PrevDiag = diag::err_previous_implicit_declaration;
@@ -848,8 +853,18 @@ Sema::ActOnDeclarator(Scope *S, Declarator &D, DeclTy *lastDecl) {
     // Merge the decl with the existing one if appropriate. Since C functions
     // are in a flat namespace, make sure we consider decls in outer scopes.
     if (PrevDecl) {
-      NewFD = MergeFunctionDecl(NewFD, PrevDecl);
+      bool Redeclaration = false;
+      NewFD = MergeFunctionDecl(NewFD, PrevDecl, Redeclaration);
       if (NewFD == 0) return 0;
+      if (Redeclaration) {
+        // Note that the new declaration is a redeclaration of the
+        // older declaration. Then return the older declaration: the
+        // new one is only kept within the set of previous
+        // declarations for this function.
+        FunctionDecl *OldFD = (FunctionDecl *)PrevDecl;
+        OldFD->AddRedeclaration(NewFD);
+        return OldFD;
+      }
     }
     New = NewFD;
 
@@ -1177,10 +1192,11 @@ Sema::DeclTy *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Declarator &D) {
   Decl *PrevDcl = LookupDecl(D.getIdentifier(), Decl::IDNS_Ordinary,
                              GlobalScope);
   if (FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(PrevDcl)) {
-    if (FD->getBody()) {
+    const FunctionDecl *Definition;
+    if (FD->getBody(Definition)) {
       Diag(D.getIdentifierLoc(), diag::err_redefinition, 
            D.getIdentifier()->getName());
-      Diag(FD->getLocation(), diag::err_previous_definition);
+      Diag(Definition->getLocation(), diag::err_previous_definition);
     }
   }
   Decl *decl = static_cast<Decl*>(ActOnDeclarator(GlobalScope, D, 0));