[modules] PR28752: Do not instantiate variable declarations which are not visible.

https://reviews.llvm.org/D24508

Patch developed in collaboration with Richard Smith!

llvm-svn: 283882

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 19113da7e3c..864eaf02b02 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -1216,6 +1216,7 @@ ASTDeclReader::RedeclarableResult ASTDeclReader::VisitVarDeclImpl(VarDecl *VD) {
   VD->VarDeclBits.TSCSpec = Record[Idx++];
   VD->VarDeclBits.InitStyle = Record[Idx++];
   if (!isa<ParmVarDecl>(VD)) {
+    VD->NonParmVarDeclBits.IsThisDeclarationADemotedDefinition = Record[Idx++];
     VD->NonParmVarDeclBits.ExceptionVar = Record[Idx++];
     VD->NonParmVarDeclBits.NRVOVariable = Record[Idx++];
     VD->NonParmVarDeclBits.CXXForRangeDecl = Record[Idx++];
@@ -3069,6 +3070,34 @@ void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
 namespace clang {
 template<>
 void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
+                                           Redeclarable<VarDecl> *D,
+                                           Decl *Previous, Decl *Canon) {
+  VarDecl *VD = static_cast<VarDecl*>(D);
+  VarDecl *PrevVD = cast<VarDecl>(Previous);
+  D->RedeclLink.setPrevious(PrevVD);
+  D->First = PrevVD->First;
+
+
+  // We should keep at most one definition on the chain.
+  if (VD->isThisDeclarationADefinition()) {
+    for (VarDecl *CurD = PrevVD; CurD; CurD = CurD->getPreviousDecl()) {
+      // If we find an already demoted definition, this we already visited this
+      // part of the chain. Reduces the loop from quadratic-time to linear-time.
+      if (CurD->isThisDeclarationADemotedDefinition()) {
+        VD->demoteThisDefinitionToDeclaration();
+        break;
+      }
+      if (CurD->isThisDeclarationADefinition()) {
+        // If we found another definition on the chain, demote the current one.
+        VD->demoteThisDefinitionToDeclaration();
+        break;
+      }
+    }
+  }
+}
+
+template<>
+void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
                                            Redeclarable<FunctionDecl> *D,
                                            Decl *Previous, Decl *Canon) {
   FunctionDecl *FD = static_cast<FunctionDecl*>(D);