[clang][Interp] Implement ImplicitValueInitExprs

Take the existing Zero opcode and emit it.

Differential Revision: https://reviews.llvm.org/D132829

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -223,6 +223,14 @@ bool ByteCodeExprGen<Emitter>::VisitBinaryOperator(const BinaryOperator *BO) {
   return this->bail(BO);
 }
 
+template <class Emitter>
+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>::discard(const Expr *E) {
   OptionScope<Emitter> Scope(this, /*NewDiscardResult=*/true);

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -75,6 +75,7 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   bool VisitCXXNullPtrLiteralExpr(const CXXNullPtrLiteralExpr *E);
   bool VisitUnaryOperator(const UnaryOperator *E);
   bool VisitDeclRefExpr(const DeclRefExpr *E);
+  bool VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;

clang/lib/AST/Interp/Opcodes.td

@@ -203,6 +203,7 @@ def ConstBool : ConstOpcode<Bool, ArgBool>;
 // [] -> [Integer]
 def Zero : Opcode {
   let Types = [AluTypeClass];
+  let HasGroup = 1;
 }
 
 // [] -> [Pointer]

clang/test/AST/Interp/arrays.cpp

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify %s
+// RUN: %clang_cc1 -verify=ref %s
+
+
+/// expected-no-diagnostics
+/// ref-no-diagnostics
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc99-extensions"
+#pragma clang diagnostic ignored "-Winitializer-overrides"
+/// FIXME: The example below tests ImplicitValueInitExprs, but we can't
+///   currently evaluate other parts of it.
+#if 0
+struct fred {
+  char s [6];
+  int n;
+};
+
+struct fred y [] = { [0] = { .s[0] = 'q' } };
+#endif
+#pragma clang diagnostic pop