[Driver] Remove -fno-concept-satisfaction-caching

[ilya-biryukov]

Summary

The flag was added when the C++20 draft did not allow for concept
caching. The final C++20 standard permits the caching, so flag is
redundant. See http://wg21.link/p2104r0.

clang/docs/ReleaseNotes.rst

 Deprecated Compiler Flags
 -------------------------
 
 Modified Compiler Flags
 -----------------------
 
 Removed Compiler Flags
 -------------------------
+- Removed the ``-fno-concept-satisfaction-caching`` flag. The flag was added
+  at the time when the draft of C++20 standard did not permit caching of
+  atomic constraints. The final standard permits such caching, see
+  `WG21 P2104R0<http://wg21.link/p2104r0>`_.
 
 New Pragmas in Clang
 --------------------
 
 - ...
 
 Attribute Changes in Clang
 --------------------------

clang/include/clang/Basic/LangOptions.def

 ENUM_LANGOPT(SYCLVersion  , SYCLMajorVersion, 2, SYCL_None, "Version of the SYCL standard used")
 
 LANGOPT(HIPUseNewLaunchAPI, 1, 0, "Use new kernel launching API for HIP")
 
 LANGOPT(SizedDeallocation , 1, 0, "sized deallocation")
 LANGOPT(AlignedAllocation , 1, 0, "aligned allocation")
 LANGOPT(AlignedAllocationUnavailable, 1, 0, "aligned allocation functions are unavailable")
 LANGOPT(NewAlignOverride  , 32, 0, "maximum alignment guaranteed by '::operator new(size_t)'")
-LANGOPT(ConceptSatisfactionCaching , 1, 1, "enable satisfaction caching for C++20 Concepts")
 BENIGN_LANGOPT(ModulesCodegen , 1, 0, "Modules code generation")
 BENIGN_LANGOPT(ModulesDebugInfo , 1, 0, "Modules debug info")
 BENIGN_LANGOPT(ElideConstructors , 1, 1, "C++ copy constructor elision")
 BENIGN_LANGOPT(DumpRecordLayouts , 1, 0, "dumping the layout of IRgen'd records")
 BENIGN_LANGOPT(DumpRecordLayoutsSimple , 1, 0, "dumping the layout of IRgen'd records in a simple form")
 BENIGN_LANGOPT(DumpRecordLayoutsCanonical , 1, 0, "dumping the AST layout of records using canonical field types")
 BENIGN_LANGOPT(DumpRecordLayoutsComplete , 1, 0, "dumping the AST layout of all complete records")
 BENIGN_LANGOPT(DumpVTableLayouts , 1, 0, "dumping the layouts of emitted vtables")

clang/include/clang/Driver/Options.td

HelpText<"Select the container format for clang modules and PCH. "
            "Supported options are 'raw' and 'obj'.">,
   MarshallingInfoString<HeaderSearchOpts<"ModuleFormat">, [{"raw"}]>;
 def ftest_module_file_extension_EQ :
   Joined<["-"], "ftest-module-file-extension=">,
   HelpText<"introduce a module file extension for testing purposes. "
            "The argument is parsed as blockname:major:minor:hashed:user info">;
 def fconcepts_ts : Flag<["-"], "fconcepts-ts">,
   HelpText<"Enable C++ Extensions for Concepts. (deprecated - use -std=c++2a)">;
-def fno_concept_satisfaction_caching : Flag<["-"],
-                                            "fno-concept-satisfaction-caching">,
-  HelpText<"Disable satisfaction caching for C++2a Concepts.">,
-  MarshallingInfoNegativeFlag<LangOpts<"ConceptSatisfactionCaching">>;
 
 defm recovery_ast : BoolOption<"f", "recovery-ast",
   LangOpts<"RecoveryAST">, DefaultTrue,
   NegFlag<SetFalse>, PosFlag<SetTrue, [], "Preserve expressions in AST rather "
                               "than dropping them when encountering semantic errors">>;
 defm recovery_ast_type : BoolOption<"f", "recovery-ast-type",
   LangOpts<"RecoveryASTType">, DefaultTrue,
   NegFlag<SetFalse>, PosFlag<SetTrue, [], "Preserve the type for recovery "

clang/lib/Sema/SemaConcept.cpp

 bool Sema::CheckConstraintSatisfaction(
     const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
     ArrayRef<TemplateArgument> TemplateArgs, SourceRange TemplateIDRange,
     ConstraintSatisfaction &OutSatisfaction) {
   if (ConstraintExprs.empty()) {
     OutSatisfaction.IsSatisfied = true;
     return false;
   }
-
-  bool ShouldCache = LangOpts.ConceptSatisfactionCaching && Template;
-  if (!ShouldCache) {
-    return ::CheckConstraintSatisfaction(*this, Template, ConstraintExprs,
+  if (!Template) {
+    return ::CheckConstraintSatisfaction(*this, nullptr, ConstraintExprs,
                                          TemplateArgs, TemplateIDRange,
                                          OutSatisfaction);
   }
   llvm::FoldingSetNodeID ID;
   ConstraintSatisfaction::Profile(ID, Context, Template, TemplateArgs);
   void *InsertPos;
   if (auto *Cached = SatisfactionCache.FindNodeOrInsertPos(ID, InsertPos)) {
     OutSatisfaction = *Cached;

clang/test/SemaTemplate/cxx2a-constraint-caching.cpp

 // RUN:  %clang_cc1 -std=c++2a -verify %s
-// RUN:  %clang_cc1 -std=c++2a -verify %s -fno-concept-satisfaction-caching -DNO_CACHE
 // expected-no-diagnostics
 
 template<typename T>
 concept C = (f(T()), true);
 
 template<typename T>
 constexpr bool foo() { return false; }
 

 static_assert(C<a::A>);
 static_assert(foo<a::A>());
 
 namespace a {
   // This makes calls to f ambiguous, but the second check will still succeed
   // because the constraint satisfaction results are cached.
   constexpr void f(A a, int = 2) {}
 }
-#ifdef NO_CACHE
-static_assert(!C<a::A>);
-static_assert(!foo<a::A>());
-#else
 static_assert(C<a::A>);
 static_assert(foo<a::A>());
-#endif