[clang][Interp] Handle SubstNonTypeTemplateParmExprs

[tbaeder]

Summary

These are also easy to add and used in a unit test that I'd like to get working with the new interpreter.

[shafik]

Makes sense to me.

[erichkeane]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

237

Is there nothing special that has to happen when these are reference parameters? Can you at least add a test for that?

[tbaeder]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

237

Umm, I don't really do references yet (I haven't tested them at all and I don't think they are implemented).

[erichkeane]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

237

Hmm... that is unfortunate. We really should be doing references ASAP, as they are going to be a pretty critical/oft-needed during testing kinda thing. I'd at least want a commented-out test that you can re-enable ASAP.

[tahonermann]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

237

Are not-yet-implemented features consistently implemented such that constant evaluation will fail with a (possibly unhelpful) diagnostic? As in https://godbolt.org/z/8vvdca9Ma? If so, can tests be added ahead of time with annotations for expected errors (essentially false positives to be addressed later)?

[tbaeder]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

237

Some are always (like unhandled AST node), some are not.

[tbaeder]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

237

An example for this with a reference type is in https://reviews.llvm.org/D132997

[aaron.ballman]

LGTM on the assumption that the extra test coverage doesn't find anything.

clang/test/AST/Interp/functions.cpp

68–69

70–75

Can you also add a use where there's a default argument for the NTTP just to make sure we get that right too? (I'd be surprised if it didn't.)

clang/lib/AST/Interp/ByteCodeExprGen.h

public:
   bool VisitBinaryOperator(const BinaryOperator *E);
   bool VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E);
   bool VisitCallExpr(const CallExpr *E);
   bool VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E);
   bool VisitCXXNullPtrLiteralExpr(const CXXNullPtrLiteralExpr *E);
   bool VisitUnaryOperator(const UnaryOperator *E);
   bool VisitDeclRefExpr(const DeclRefExpr *E);
   bool VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E);
+  bool VisitSubstNonTypeTemplateParmExpr(const SubstNonTypeTemplateParmExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;
   bool visitDecl(const VarDecl *VD) override;
 
 protected:
   /// Emits scope cleanup instructions.
   void emitCleanup();

clang/lib/AST/Interp/ByteCodeExprGen.cpp

 bool ByteCodeExprGen<Emitter>::VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
   if (Optional<PrimType> T = classify(E))
     return this->emitZero(*T, E);
 
   return false;
 }
 
 template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitSubstNonTypeTemplateParmExpr(
+    const SubstNonTypeTemplateParmExpr *E) {
+  return this->visit(E->getReplacement());
+}
+
+template <class Emitter>
 bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   OptionScope<Emitter> Scope(this, /*NewDiscardResult=*/true);
   return this->Visit(E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::visit(const Expr *E) {
   OptionScope<Emitter> Scope(this, /*NewDiscardResult=*/false);

clang/test/AST/Interp/functions.cpp

constexpr int recursion(int i) {
   doNothing();
   i = i - 1;
   if (i == 0)
     return identity(0);
 
   return recursion(i);
 }
 static_assert(recursion(10) == 0, "");
+
+template<int N = 5>
+constexpr decltype(N) getNum() {
+  return N;
+}
+static_assert(getNum<-2>() == -2, "");
+static_assert(getNum<10>() == 10, "");
+static_assert(getNum() == 5, "");