Perform type-checking for a converted constant expression in a template

argument even if the expression is value-dependent (we need to suppress the
final portion of the narrowing check, but the rest of the checking can still be
done eagerly).

This affects template template argument validity and partial ordering under
p0522r0.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290276 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 39 insertions, 11 deletions

diff --git a/include/clang/Sema/Overload.h b/include/clang/Sema/Overload.h
index 7c6699aca0..03c6a3e75b 100644
--- a/include/clang/Sema/Overload.h
+++ b/include/clang/Sema/Overload.h
@@ -121,7 +121,11 @@ namespace clang {
 
     /// A narrowing conversion, because a non-constant-expression variable might
     /// have got narrowed.
-    NK_Variable_Narrowing
+    NK_Variable_Narrowing,
+
+    /// Cannot tell whether this is a narrowing conversion because the
+    /// expression is value-dependent.
+    NK_Dependent_Narrowing,
   };
 
   /// StandardConversionSequence - represents a standard conversion
diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index 5bb5518c58..8ab14b2a63 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -6816,7 +6816,7 @@ InitializationSequence::Perform(Sema &S,
       CurInit = CurInitExprRes;
 
       if (Step->Kind == SK_ConversionSequenceNoNarrowing &&
-          S.getLangOpts().CPlusPlus && !CurInit.get()->isValueDependent())
+          S.getLangOpts().CPlusPlus)
         DiagnoseNarrowingInInitList(S, *Step->ICS, SourceType, Entity.getType(),
                                     CurInit.get());
 
@@ -8070,6 +8070,7 @@ static void DiagnoseNarrowingInInitList(Sema &S,
   switch (SCS->getNarrowingKind(S.Context, PostInit, ConstantValue,
                                 ConstantType)) {
   case NK_Not_Narrowing:
+  case NK_Dependent_Narrowing:
     // No narrowing occurred.
     return;
 
diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 2129729dab..fb378b86af 100644
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -329,6 +329,11 @@ StandardConversionSequence::getNarrowingKind(ASTContext &Ctx,
     } else if (FromType->isIntegralType(Ctx) && ToType->isRealFloatingType()) {
       llvm::APSInt IntConstantValue;
       const Expr *Initializer = IgnoreNarrowingConversion(Converted);
+
+      // If it's value-dependent, we can't tell whether it's narrowing.
+      if (Initializer->isValueDependent())
+        return NK_Dependent_Narrowing;
+
       if (Initializer &&
           Initializer->isIntegerConstantExpr(IntConstantValue, Ctx)) {
         // Convert the integer to the floating type.
@@ -362,6 +367,11 @@ StandardConversionSequence::getNarrowingKind(ASTContext &Ctx,
         Ctx.getFloatingTypeOrder(FromType, ToType) == 1) {
       // FromType is larger than ToType.
       const Expr *Initializer = IgnoreNarrowingConversion(Converted);
+
+      // If it's value-dependent, we can't tell whether it's narrowing.
+      if (Initializer->isValueDependent())
+        return NK_Dependent_Narrowing;
+
       if (Initializer->isCXX11ConstantExpr(Ctx, &ConstantValue)) {
         // Constant!
         assert(ConstantValue.isFloat());
@@ -403,6 +413,11 @@ StandardConversionSequence::getNarrowingKind(ASTContext &Ctx,
       // Not all values of FromType can be represented in ToType.
       llvm::APSInt InitializerValue;
       const Expr *Initializer = IgnoreNarrowingConversion(Converted);
+
+      // If it's value-dependent, we can't tell whether it's narrowing.
+      if (Initializer->isValueDependent())
+        return NK_Dependent_Narrowing;
+
       if (!Initializer->isIntegerConstantExpr(InitializerValue, Ctx)) {
         // Such conversions on variables are always narrowing.
         return NK_Variable_Narrowing;
@@ -5289,6 +5304,9 @@ static ExprResult CheckConvertedConstantExpression(Sema &S, Expr *From,
   QualType PreNarrowingType;
   switch (SCS->getNarrowingKind(S.Context, Result.get(), PreNarrowingValue,
                                 PreNarrowingType)) {
+  case NK_Dependent_Narrowing:
+    // Implicit conversion to a narrower type, but the expression is
+    // value-dependent so we can't tell whether it's actually narrowing.
   case NK_Variable_Narrowing:
     // Implicit conversion to a narrower type, and the value is not a constant
     // expression. We'll diagnose this in a moment.
@@ -5307,6 +5325,11 @@ static ExprResult CheckConvertedConstantExpression(Sema &S, Expr *From,
     break;
   }
 
+  if (Result.get()->isValueDependent()) {
+    Value = APValue();
+    return Result;
+  }
+
   // Check the expression is a constant expression.
   SmallVector<PartialDiagnosticAt, 8> Notes;
   Expr::EvalResult Eval;
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 9d4029a912..80567c309c 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -5059,13 +5059,6 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
   }
 
   if (getLangOpts().CPlusPlus1z) {
-    // FIXME: We can do some limited checking for a value-dependent but not
-    // type-dependent argument.
-    if (Arg->isValueDependent()) {
-      Converted = TemplateArgument(Arg);
-      return Arg;
-    }
-
     // C++1z [temp.arg.nontype]p1:
     //   A template-argument for a non-type template parameter shall be
     //   a converted constant expression of the type of the template-parameter.
@@ -5075,6 +5068,13 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
     if (ArgResult.isInvalid())
       return ExprError();
 
+    // For a value-dependent argument, CheckConvertedConstantExpression is
+    // permitted (and expected) to be unable to determine a value.
+    if (ArgResult.get()->isValueDependent()) {
+      Converted = TemplateArgument(Arg);
+      return Arg;
+    }
+
     QualType CanonParamType = Context.getCanonicalType(ParamType);
 
     // Convert the APValue to a TemplateArgument.
diff --git a/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp b/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
index 59b05a14d3..3219258572 100644
--- a/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
+++ b/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
@@ -122,13 +122,13 @@ namespace DeduceDifferentType {
   int a_exp = a<3>(A<3>());
 
   template<decltype(nullptr)> struct B {};
-  template<int *P> int b(B<P>); // expected-note {{does not have the same type}} expected-note {{not implicitly convertible}}
+  template<int *P> int b(B<P>); // expected-error {{value of type 'int *' is not implicitly convertible to 'decltype(nullptr)'}}
   int b_imp = b(B<nullptr>()); // expected-error {{no matching function}}
   int b_exp = b<nullptr>(B<nullptr>()); // expected-error {{no matching function}}
 
   struct X { constexpr operator int() { return 0; } } x;
   template<X &> struct C {};
-  template<int N> int c(C<N>); // expected-note {{does not have the same type}} expected-note {{not implicitly convertible}}
+  template<int N> int c(C<N>); // expected-error {{value of type 'int' is not implicitly convertible to 'DeduceDifferentType::X &'}}
   int c_imp = c(C<x>()); // expected-error {{no matching function}}
   int c_exp = c<x>(C<x>()); // expected-error {{no matching function}}