Try different approach withreverse order of loading specializations

Author: dmpolukhin

clang/lib/AST/DeclTemplate.cpp

@@ -349,8 +349,12 @@ void RedeclarableTemplateDecl::loadLazySpecializationsImpl() const {
     GlobalDeclID *Specs = CommonBasePtr->LazySpecializations;
     CommonBasePtr->LazySpecializations = nullptr;
     unsigned SpecSize = (*Specs++).getRawValue();
-    for (unsigned I = 0; I != SpecSize; ++I)
-      (void)Context.getExternalSource()->GetExternalDecl(Specs[I]);
+    // Load the specializations in reverse order so that the most recent
+    // specialization are visited first so they become canonical declarations.
+    // This order matches the order in which namelookup discovers declarations
+    // coming from modules.
+    for (unsigned I = SpecSize; I != 0; --I)
+      (void)Context.getExternalSource()->GetExternalDecl(Specs[I-1]);
   }
 }
 

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -4387,11 +4387,6 @@ LocalInstantiationScope::findInstantiationOf(const Decl *D) {
       // a previous declaration.
       if (const TagDecl *Tag = dyn_cast<TagDecl>(CheckD))
         CheckD = Tag->getPreviousDecl();
-      else if (const VarDecl *VD = dyn_cast<VarDecl>(CheckD))
-        // Check re-declaration chain for variable to deduplicate variables
-        // that might be captured inside lambdas. Function and lambda class
-        // inside can be loaded from different modules.
-        CheckD = VD->getPreviousDecl();
       else
         CheckD = nullptr;
     } while (CheckD);

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -3291,13 +3291,6 @@ DeclContext *ASTDeclReader::getPrimaryContextForMerging(ASTReader &Reader,
   if (auto *TU = dyn_cast<TranslationUnitDecl>(DC))
     return TU->getPrimaryContext();
 
-  // Merge VarDecls inside functions to deduplicate variables that might be
-  // captured inside lambdas. Function and lambda class inside can be loaded
-  // from different modules.
-  if (auto *FD = dyn_cast<FunctionDecl>(DC))
-    if (FD->getOwningModule())
-      return FD->getCanonicalDecl();
-
   return nullptr;
 }
 

clang/test/Modules/odr_hash.cpp

@@ -3084,8 +3084,8 @@ struct S5 {
 };
 #else
 S5 s5;
-// expected-error@second.h:* {{'PointersAndReferences::S5::x' from module 'SecondModule' is not present in definition of 'PointersAndReferences::S5' in module 'FirstModule'}}
-// expected-note@first.h:* {{declaration of 'x' does not match}}
+// expected-error@first.h:* {{'PointersAndReferences::S5::x' from module 'FirstModule' is not present in definition of 'PointersAndReferences::S5' in module 'SecondModule'}}
+// expected-note@second.h:* {{declaration of 'x' does not match}}
 #endif
 
 #if defined(FIRST)