[clang] e90792d - [clang] Update comments on another libstdc++ HACK

[Nathan Sidwell via cfe-commits]

Author: Nathan Sidwell
Date: 2021-04-30T09:29:26-07:00
New Revision: e90792d8c78bac79a1a39f245e222684ea24c7c0

URL: https://github.com/llvm/llvm-project/commit/e90792d8c78bac79a1a39f245e222684ea24c7c0
DIFF: https://github.com/llvm/llvm-project/commit/e90792d8c78bac79a1a39f245e222684ea24c7c0.diff

LOG: [clang] Update comments on another libstdc++ HACK

Document relevant gcc versions and dates.

Differential Revision: https://reviews.llvm.org/D101530

Added: 
    

Modified: 
    clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

Removed: 
    


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diff  --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index dc1e0ef60cac..cd0f13b9e32e 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -856,10 +856,11 @@ Decl *TemplateDeclInstantiator::InstantiateTypedefNameDecl(TypedefNameDecl *D,
     SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
   }
 
-  // HACK: g++ has a bug where it gets the value kind of ?: wrong.
-  // libstdc++ relies upon this bug in its implementation of common_type.
-  // If we happen to be processing that implementation, fake up the g++ ?:
-  // semantics. See LWG issue 2141 for more information on the bug.
+  // HACK: 2012-10-23 g++ has a bug where it gets the value kind of ?: wrong.
+  // libstdc++ relies upon this bug in its implementation of common_type.  If we
+  // happen to be processing that implementation, fake up the g++ ?:
+  // semantics. See LWG issue 2141 for more information on the bug.  The bugs
+  // are fixed in g++ and libstdc++ 4.9.0 (2014-04-22).
   const DecltypeType *DT = DI->getType()->getAs<DecltypeType>();
   CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D->getDeclContext());
   if (DT && RD && isa<ConditionalOperator>(DT->getUnderlyingExpr()) &&