Revert "[Clang][Sema] fix outline member function template with defau… (#80144)

…lt align crash (#78400)"

This reverts commit 7b33899.

A regression was discovered here:
#78400

and the author requested a revert to give time to review.

Author: erichkeane

clang/docs/ReleaseNotes.rst

@@ -164,10 +164,6 @@ Bug Fixes to C++ Support
 
 - Fix crash when using lifetimebound attribute in function with trailing return.
   Fixes (`#73619 <https://github.com/llvm/llvm-project/issues/73619>`_)
-- Fix a crash when specializing an out-of-line member function with a default
-  parameter where we did an incorrect specialization of the initialization of
-  the default parameter.
-  Fixes (`#68490 <https://github.com/llvm/llvm-project/issues/68490>`_)
 - Addressed an issue where constraints involving injected class types are perceived
   distinct from its specialization types.
   (`#56482 <https://github.com/llvm/llvm-project/issues/56482>`_)

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -3049,7 +3049,6 @@ bool Sema::SubstDefaultArgument(
     //   default argument expression appears.
     ContextRAII SavedContext(*this, FD);
     std::unique_ptr<LocalInstantiationScope> LIS;
-    MultiLevelTemplateArgumentList NewTemplateArgs = TemplateArgs;
 
     if (ForCallExpr) {
       // When instantiating a default argument due to use in a call expression,
@@ -3062,19 +3061,11 @@ bool Sema::SubstDefaultArgument(
           /*ForDefinition*/ false);
       if (addInstantiatedParametersToScope(FD, PatternFD, *LIS, TemplateArgs))
         return true;
-      if (FD->isOutOfLine()) {
-        TemplateArgumentList *CurrentTemplateArgumentList =
-            TemplateArgumentList::CreateCopy(getASTContext(),
-                                             TemplateArgs.getInnermost());
-        NewTemplateArgs = getTemplateInstantiationArgs(
-            FD, FD->getDeclContext(), /*Final=*/false,
-            CurrentTemplateArgumentList, /*RelativeToPrimary=*/true);
-      }
     }
 
     runWithSufficientStackSpace(Loc, [&] {
-      Result = SubstInitializer(PatternExpr, NewTemplateArgs,
-                                /*DirectInit*/ false);
+      Result = SubstInitializer(PatternExpr, TemplateArgs,
+                                /*DirectInit*/false);
     });
   }
   if (Result.isInvalid())