[SYCL][clang] Always lift SYCL device code restrictions in constexpr contexts

Earlier a mechanism to lift SYCL device code restrictions in C++
manifestly constant-evaluated expressions was implemented in the front-end.
It was enabled under an option since it wasn't specified.
Since then it has been decided to make this behavior default for SYCL 2020.
This PR removes the option that was enabling the new behavior and
enables it by default.

Author: Fznamznon

clang/include/clang/Basic/LangOptions.def

@@ -307,7 +307,6 @@ LANGOPT(SYCLAllowFuncPtr  , 1, 0, "Allow function pointers in SYCL device code")
 LANGOPT(SYCLStdLayoutKernelParams, 1, 0, "Enable standard layout requirement for SYCL kernel parameters")
 LANGOPT(SYCLUnnamedLambda , 1, 0, "Allow unnamed lambda SYCL kernels")
 LANGOPT(SYCLForceInlineKernelLambda , 1, 0, "Force inline SYCL kernel lambdas in entry point")
-LANGOPT(SYCLAllowAllFeaturesInConstexpr, 1, 0, "Allow all C++ features in SYCL device code in manifestly constant-evaluated expressions")
 LANGOPT(SYCLESIMDForceStatelessMem, 1, 0, "Make accessors use USM memory in ESIMD kernels")
 LANGOPT(SYCLESIMDBuildHostCode, 1, 1, "Build the host implementation of ESIMD functions")
 ENUM_LANGOPT(SYCLVersion  , SYCLMajorVersion, 2, SYCL_None, "Version of the SYCL standard used")

clang/include/clang/Driver/Options.td

@@ -8628,11 +8628,6 @@ def fsycl_is_native_cpu : Flag<["-"], "fsycl-is-native-cpu">,
   HelpText<"Perform device compilation for Native CPU.">,
   Visibility<[CC1Option]>,
   MarshallingInfoFlag<LangOpts<"SYCLIsNativeCPU">>;
-defm sycl_allow_all_features_in_constexpr
-    : BoolFOption<
-          "sycl-allow-all-features-in-constexpr", LangOpts<"SYCLAllowAllFeaturesInConstexpr">,
-          DefaultFalse,
-          PosFlag<SetTrue, [], [CC1Option], "Allow all C++ features in SYCL device code in manifestly constant-evaluated expressions">, NegFlag<SetFalse>>;
 
 } // let Visibility = [CC1Option]
 

clang/lib/Sema/Sema.cpp

@@ -1829,7 +1829,7 @@ class DeferredDiagnosticsEmitter
   }
 
   void VisitDeclStmt(DeclStmt *DS) {
-    if (S.getLangOpts().SYCLAllowAllFeaturesInConstexpr) {
+    if (S.getLangOpts().SYCLIsDevice) {
       if (DS->isSingleDecl()) {
         Decl *D = DS->getSingleDecl();
         if (auto *VD = dyn_cast<VarDecl>(D))
@@ -1850,7 +1850,7 @@ class DeferredDiagnosticsEmitter
   }
 
   void VisitConstantExpr(ConstantExpr *E) {
-    if (S.getLangOpts().SYCLAllowAllFeaturesInConstexpr)
+    if (S.getLangOpts().SYCLIsDevice)
       return;
     this->VisitStmt(E);
   }
@@ -2264,7 +2264,7 @@ void Sema::checkTypeSupport(QualType Ty, SourceLocation Loc, ValueDecl *D) {
 
   CheckType(Ty);
   if (const auto *FD = dyn_cast_if_present<FunctionDecl>(D)) {
-    if (LangOpts.SYCLAllowAllFeaturesInConstexpr && FD->isConsteval())
+    if (LangOpts.SYCLIsDevice && FD->isConsteval())
       return;
     if (const auto *FPTy = dyn_cast<FunctionProtoType>(Ty)) {
       for (const auto &ParamTy : FPTy->param_types())

clang/lib/Sema/SemaDeclCXX.cpp

@@ -18418,7 +18418,7 @@ void Sema::ActOnCXXEnterDeclInitializer(Scope *S, Decl *D) {
 
   if (auto *VD = dyn_cast<VarDecl>(D);
       VD && (VD->mightBeUsableInConstantExpressions(Context)))
-    InConstexprVarInit = LangOpts.SYCLAllowAllFeaturesInConstexpr;
+    InConstexprVarInit = true;
   PushExpressionEvaluationContext(
       ExpressionEvaluationContext::PotentiallyEvaluated, D);
 }

clang/lib/Sema/SemaSYCL.cpp

@@ -782,8 +782,7 @@ class DeviceFunctionTracker {
 
 public:
   DeviceFunctionTracker(SemaSYCL &S) : SemaSYCLRef(S) {
-    if (S.getLangOpts().SYCLAllowAllFeaturesInConstexpr)
-      CG.setSkipConstantExpressions(S.getASTContext());
+    CG.setSkipConstantExpressions(S.getASTContext());
     CG.addToCallGraph(S.getASTContext().getTranslationUnitDecl());
     CollectSyclExternalFuncs();
   }
@@ -5594,14 +5593,12 @@ SemaSYCL::DiagIfDeviceCode(SourceLocation Loc, unsigned DiagID,
       return SemaDiagnosticBuilder::K_ImmediateWithCallStack;
     if (!FD)
       return SemaDiagnosticBuilder::K_Nop;
-    if (SemaRef.getLangOpts().SYCLAllowAllFeaturesInConstexpr &&
-        (SemaRef.isConstantEvaluatedContext() ||
-         SemaRef.currentEvaluationContext().isDiscardedStatementContext()))
+    if (SemaRef.isConstantEvaluatedContext() ||
+        SemaRef.currentEvaluationContext().isDiscardedStatementContext())
       return SemaDiagnosticBuilder::K_Nop;
     // Defer until we know that the variable's intializer is actually a
     // manifestly constant-evaluated expression.
-    if (SemaRef.getLangOpts().SYCLAllowAllFeaturesInConstexpr &&
-        SemaRef.InConstexprVarInit)
+    if (SemaRef.InConstexprVarInit)
       return SemaDiagnosticBuilder::K_Deferred;
     if (SemaRef.getEmissionStatus(FD) ==
         Sema::FunctionEmissionStatus::Emitted) {

clang/test/SemaSYCL/allow-all-features-in-constexpr.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsycl-is-device -internal-isystem %S/Inputs -fcxx-exceptions -verify -fsyntax-only -std=c++23 -triple spir64 -aux-triple x86_64 -fsycl-allow-all-features-in-constexpr %s
+// RUN: %clang_cc1 -fsycl-is-device -internal-isystem %S/Inputs -fcxx-exceptions -verify -fsyntax-only -std=c++23 -triple spir64 -aux-triple x86_64 %s
 
 // The test checks that all SYCL device code limitations are lifted in
 // manifestly constant-evaluated expressions under an option.

clang/test/SemaSYCL/wrong-address-taking.cpp

@@ -50,7 +50,6 @@ template <typename T> void templatedContext() {
   // expected-error@+1 {{taking address of a function not marked with 'intel::device_indirectly_callable' attribute is not allowed in SYCL device code}}
   auto p1 = &ForMembers::badMember;
 
-  // expected-error@+2 {{taking address of a function not marked with 'intel::device_indirectly_callable' attribute is not allowed in SYCL device code}}
   // expected-note@+1 {{called by 'templatedContext<int>'}}
   templateCaller1<badFoo>(1);
 }
@@ -84,9 +83,7 @@ int main() {
           a = goodFoo;
           a = &goodFoo;
 
-          // expected-error@+1 {{taking address of a function not marked with 'intel::device_indirectly_callable' attribute is not allowed in SYCL device code}}
           constexpr auto b = badFoo;
-          // expected-error@+1 {{taking address of a function not marked with 'intel::device_indirectly_callable' attribute is not allowed in SYCL device code}}
           constexpr auto c = &badFoo;
           // expected-note@+1 {{called by 'operator()'}}
           basicUsage();
@@ -125,8 +122,7 @@ int main() {
 
           templateCaller1<goodFoo>(1);
 
-          // expected-note@+2 {{called by 'operator()'}}
-          // expected-error@+1 {{taking address of a function not marked with 'intel::device_indirectly_callable' attribute is not allowed in SYCL device code}}
+          // expected-note@+1 {{called by 'operator()'}}
           templateCaller1<badFoo>(1);
         });
   });