Revert "[Clang] Improve infrastructure for libstdc++ workarounds" (#142432)

Reverts #141977

This causes CI failure that I am unable to reproduce.
https://lab.llvm.org/buildbot/#/builders/168/builds/12688

Author: cor3ntin

clang/include/clang/Lex/Preprocessor.h

@@ -129,12 +129,6 @@ enum class EmbedResult {
   Empty = 2,    // Corresponds to __STDC_EMBED_EMPTY__
 };
 
-struct CXXStandardLibraryVersionInfo {
-  enum Library { Unknown, LibStdCXX };
-  Library Lib;
-  unsigned Version;
-};
-
 /// Engages in a tight little dance with the lexer to efficiently
 /// preprocess tokens.
 ///
@@ -2712,15 +2706,6 @@ class Preprocessor {
     return IsFileLexer(CurLexer.get(), CurPPLexer);
   }
 
-  //===--------------------------------------------------------------------===//
-  // Standard Library Identification
-  std::optional<CXXStandardLibraryVersionInfo> CXXStandardLibraryVersion;
-
-public:
-  std::optional<unsigned> getStdLibCxxVersion();
-  bool NeedsStdLibCxxWorkaroundBefore(unsigned FixedVersion);
-
-private:
   //===--------------------------------------------------------------------===//
   // Caching stuff.
   void CachingLex(Token &Result);

clang/lib/Lex/PPExpressions.cpp

@@ -979,49 +979,3 @@ Preprocessor::EvaluateDirectiveExpression(IdentifierInfo *&IfNDefMacro,
   return EvaluateDirectiveExpression(IfNDefMacro, Tok, EvaluatedDefined,
                                      CheckForEoD);
 }
-
-static std::optional<CXXStandardLibraryVersionInfo>
-getCXXStandardLibraryVersion(Preprocessor &PP, StringRef MacroName,
-                             CXXStandardLibraryVersionInfo::Library Lib) {
-  MacroInfo *Macro = PP.getMacroInfo(PP.getIdentifierInfo(MacroName));
-
-  if (!Macro || Macro->getNumTokens() != 1 || !Macro->isObjectLike())
-    return std::nullopt;
-
-  const Token &RevisionDateTok = Macro->getReplacementToken(0);
-
-  bool Invalid = false;
-  llvm::SmallVector<char, 10> Buffer;
-  llvm::StringRef RevisionDate =
-      PP.getSpelling(RevisionDateTok, Buffer, &Invalid);
-  if (!Invalid) {
-    unsigned Value;
-    // We don't use NumericParser to avoid diagnostics
-    if (!RevisionDate.consumeInteger(10, Value))
-      return CXXStandardLibraryVersionInfo{Lib, Value};
-  }
-  return CXXStandardLibraryVersionInfo{CXXStandardLibraryVersionInfo::Unknown,
-                                       0};
-}
-
-std::optional<unsigned> Preprocessor::getStdLibCxxVersion() {
-  if (!CXXStandardLibraryVersion)
-    CXXStandardLibraryVersion = getCXXStandardLibraryVersion(
-        *this, "__GLIBCXX__", CXXStandardLibraryVersionInfo::LibStdCXX);
-  if (!CXXStandardLibraryVersion)
-    return std::nullopt;
-
-  if (CXXStandardLibraryVersion->Lib ==
-      CXXStandardLibraryVersionInfo::LibStdCXX)
-    return CXXStandardLibraryVersion->Version;
-  return std::nullopt;
-}
-
-bool Preprocessor::NeedsStdLibCxxWorkaroundBefore(unsigned FixedVersion) {
-  assert(FixedVersion >= 2000'00'00 && FixedVersion <= 2100'00'00 &&
-         "invalid value for __GLIBCXX__");
-  std::optional<unsigned> Ver = getStdLibCxxVersion();
-  if (!Ver)
-    return false;
-  return *Ver < FixedVersion;
-}

clang/lib/Sema/SemaDeclCXX.cpp

@@ -13198,7 +13198,6 @@ NamedDecl *Sema::BuildUsingDeclaration(
     if (getLangOpts().CPlusPlus14 && II && II->isStr("gets") &&
         CurContext->isStdNamespace() &&
         isa<TranslationUnitDecl>(LookupContext) &&
-        PP.NeedsStdLibCxxWorkaroundBefore(2016'12'21) &&
         getSourceManager().isInSystemHeader(UsingLoc))
       return nullptr;
     UsingValidatorCCC CCC(HasTypenameKeyword, IsInstantiation, SS.getScopeRep(),

clang/lib/Sema/SemaExceptionSpec.cpp

@@ -18,7 +18,6 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/SourceManager.h"
-#include "clang/Lex/Preprocessor.h"
 #include "clang/Sema/SemaInternal.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include <optional>
@@ -45,8 +44,6 @@ static const FunctionProtoType *GetUnderlyingFunction(QualType T)
 bool Sema::isLibstdcxxEagerExceptionSpecHack(const Declarator &D) {
   auto *RD = dyn_cast<CXXRecordDecl>(CurContext);
 
-  if (!getPreprocessor().NeedsStdLibCxxWorkaroundBefore(2016'04'27))
-    return false;
   // All the problem cases are member functions named "swap" within class
   // templates declared directly within namespace std or std::__debug or
   // std::__profile.

clang/lib/Sema/SemaInit.cpp

@@ -21,7 +21,6 @@
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Basic/TargetInfo.h"
-#include "clang/Lex/Preprocessor.h"
 #include "clang/Sema/Designator.h"
 #include "clang/Sema/EnterExpressionEvaluationContext.h"
 #include "clang/Sema/Initialization.h"
@@ -642,10 +641,8 @@ ExprResult InitListChecker::PerformEmptyInit(SourceLocation Loc,
   // in that case. stlport does so too.
   // Look for std::__debug for libstdc++, and for std:: for stlport.
   // This is effectively a compiler-side implementation of LWG2193.
-  if (!InitSeq && EmptyInitList &&
-      InitSeq.getFailureKind() ==
-          InitializationSequence::FK_ExplicitConstructor &&
-      SemaRef.getPreprocessor().NeedsStdLibCxxWorkaroundBefore(2014'04'22)) {
+  if (!InitSeq && EmptyInitList && InitSeq.getFailureKind() ==
+          InitializationSequence::FK_ExplicitConstructor) {
     OverloadCandidateSet::iterator Best;
     OverloadingResult O =
         InitSeq.getFailedCandidateSet()

clang/lib/Sema/SemaTemplate.cpp

@@ -4444,16 +4444,35 @@ static bool IsLibstdcxxStdFormatKind(Preprocessor &PP, VarDecl *Var) {
       !Var->getDeclContext()->isStdNamespace())
     return false;
 
-  // Checking old versions of libstdc++ is not needed because 15.1 is the first
-  // release in which users can access std::format_kind.
+  MacroInfo *MacroGLIBCXX =
+      PP.getMacroInfo(PP.getIdentifierInfo("__GLIBCXX__"));
+
+  if (!MacroGLIBCXX || MacroGLIBCXX->getNumTokens() != 1)
+    return false;
+
+  const Token &RevisionDateTok = MacroGLIBCXX->getReplacementToken(0);
+  bool Invalid = false;
+  std::string RevisionDate = PP.getSpelling(RevisionDateTok, &Invalid);
+
   // We can use 20250520 as the final date, see the following commits.
   // GCC releases/gcc-15 branch:
   // https://gcc.gnu.org/g:fedf81ef7b98e5c9ac899b8641bb670746c51205
   // https://gcc.gnu.org/g:53680c1aa92d9f78e8255fbf696c0ed36f160650
   // GCC master branch:
   // https://gcc.gnu.org/g:9361966d80f625c5accc25cbb439f0278dd8b278
   // https://gcc.gnu.org/g:c65725eccbabf3b9b5965f27fff2d3b9f6c75930
-  return PP.NeedsStdLibCxxWorkaroundBefore(2025'05'20);
+  StringRef FixDate = "20250520";
+
+  if (Invalid)
+    return false;
+
+  // The format of the revision date is in compressed ISO date format.
+  // See https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_macros.html
+  // So we can use string comparison.
+  //
+  // Checking old versions of libstdc++ is not needed because 15.1 is the first
+  // release in which users can access std::format_kind.
+  return RevisionDate.size() == 8 && RevisionDate < FixDate;
 }
 } // end anonymous namespace
 

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1448,19 +1448,17 @@ Decl *TemplateDeclInstantiator::InstantiateTypedefNameDecl(TypedefNameDecl *D,
   // 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).
-  if (SemaRef.getPreprocessor().NeedsStdLibCxxWorkaroundBefore(2014'04'22)) {
-    const DecltypeType *DT = DI->getType()->getAs<DecltypeType>();
-    CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D->getDeclContext());
-    if (DT && RD && isa<ConditionalOperator>(DT->getUnderlyingExpr()) &&
-        DT->isReferenceType() &&
-        RD->getEnclosingNamespaceContext() == SemaRef.getStdNamespace() &&
-        RD->getIdentifier() && RD->getIdentifier()->isStr("common_type") &&
-        D->getIdentifier() && D->getIdentifier()->isStr("type") &&
-        SemaRef.getSourceManager().isInSystemHeader(D->getBeginLoc()))
-      // Fold it to the (non-reference) type which g++ would have produced.
-      DI = SemaRef.Context.getTrivialTypeSourceInfo(
-          DI->getType().getNonReferenceType());
-  }
+  const DecltypeType *DT = DI->getType()->getAs<DecltypeType>();
+  CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D->getDeclContext());
+  if (DT && RD && isa<ConditionalOperator>(DT->getUnderlyingExpr()) &&
+      DT->isReferenceType() &&
+      RD->getEnclosingNamespaceContext() == SemaRef.getStdNamespace() &&
+      RD->getIdentifier() && RD->getIdentifier()->isStr("common_type") &&
+      D->getIdentifier() && D->getIdentifier()->isStr("type") &&
+      SemaRef.getSourceManager().isInSystemHeader(D->getBeginLoc()))
+    // Fold it to the (non-reference) type which g++ would have produced.
+    DI = SemaRef.Context.getTrivialTypeSourceInfo(
+      DI->getType().getNonReferenceType());
 
   // Create the new typedef
   TypedefNameDecl *Typedef;

clang/test/SemaCXX/libstdcxx_common_type_hack.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -D__GLIBCXX__=20100000L
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify
 
 // This is a test for an egregious hack in Clang that works around
 // an issue with GCC's <type_traits> implementation. std::common_type

clang/test/SemaCXX/libstdcxx_explicit_init_list_hack.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -Wsystem-headers -D__GLIBCXX__=20100000L %s
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -Wsystem-headers %s
 
 // libstdc++4.6 in debug mode has explicit default constructors.
 // stlport has this for all containers.

clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp

@@ -7,20 +7,20 @@
 // The same problem afflicts a bunch of other class templates. Those
 // affected are array, pair, priority_queue, stack, and queue.
 
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array -DPR28423
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=pair
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=priority_queue
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=stack
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=queue
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=array
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=array -DPR28423
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=pair
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=priority_queue
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=stack
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=queue
 //
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array -DNAMESPACE=__debug
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array -DNAMESPACE=__profile
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=array -DNAMESPACE=__debug
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=array -DNAMESPACE=__profile
 
 // MSVC's standard library uses a very similar pattern that relies on delayed
 // parsing of exception specifications.
 //
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array -DMSVC
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify -fexceptions -fcxx-exceptions -DCLASS=array -DMSVC
 
 #ifdef BE_THE_HEADER