Index: clang/lib/AST/Interp/Boolean.h
===================================================================
--- clang/lib/AST/Interp/Boolean.h
+++ clang/lib/AST/Interp/Boolean.h
@@ -50,6 +50,7 @@
   explicit operator int64_t() const { return V; }
   explicit operator uint64_t() const { return V; }
   explicit operator int() const { return V; }
+  explicit operator bool() const { return V; }
 
   APSInt toAPSInt() const {
     return APSInt(APInt(1, static_cast<uint64_t>(V), false), true);
@@ -85,9 +86,10 @@
   static Boolean min(unsigned NumBits) { return Boolean(false); }
   static Boolean max(unsigned NumBits) { return Boolean(true); }
 
-  template <typename T>
-  static std::enable_if_t<std::is_integral<T>::value, Boolean> from(T Value) {
-    return Boolean(Value != 0);
+  template <typename T> static Boolean from(T Value) {
+    if constexpr (std::is_integral<T>::value)
+      return Boolean(Value != 0);
+    return Boolean(static_cast<decltype(Boolean::V)>(Value) != 0);
   }
 
   template <unsigned SrcBits, bool SrcSign>
Index: clang/lib/AST/Interp/ByteCodeExprGen.cpp
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -117,6 +117,7 @@
   case CK_NullToPointer:
     return this->Visit(SubExpr);
 
+  case CK_IntegralToBoolean:
   case CK_IntegralCast: {
     Optional<PrimType> FromT = classify(SubExpr->getType());
     Optional<PrimType> ToT = classify(CE->getType());
@@ -132,19 +133,6 @@
   case CK_ToVoid:
     return discard(SubExpr);
 
-  case CK_IntegralToBoolean:
-    // Compare integral from Subexpr with 0
-    if (Optional<PrimType> T = classify(SubExpr->getType())) {
-      if (!this->Visit(SubExpr))
-        return false;
-
-      if (!this->emitConst(SubExpr, 0))
-        return false;
-
-      return this->emitNE(*T, SubExpr);
-    }
-    return false;
-
   default:
     assert(false && "Cast not implemented");
   }
Index: clang/lib/AST/Interp/Opcodes.td
===================================================================
--- clang/lib/AST/Interp/Opcodes.td
+++ clang/lib/AST/Interp/Opcodes.td
@@ -425,12 +425,16 @@
 //===----------------------------------------------------------------------===//
 // TODO: Expand this to handle casts between more types.
 
-def Sint32TypeClass : TypeClass {
-  let Types = [Sint32];
+def FromCastTypeClass : TypeClass {
+  let Types = [Sint32, Bool];
+}
+
+def ToCastTypeClass : TypeClass {
+  let Types = [Sint32, Bool];
 }
 
 def Cast: Opcode {
-  let Types = [BoolTypeClass, Sint32TypeClass];
+  let Types = [FromCastTypeClass, ToCastTypeClass];
   let HasGroup = 1;
 }
 
Index: clang/test/AST/Interp/literals.cpp
===================================================================
--- clang/test/AST/Interp/literals.cpp
+++ clang/test/AST/Interp/literals.cpp
@@ -14,6 +14,11 @@
                                  // expected-note{{evaluates to}} \
                                  // ref-note{{evaluates to}}
 
+constexpr bool b = number;
+static_assert(b, "");
+constexpr int one = true;
+static_assert(one == 1, "");
+
 constexpr bool getTrue() { return true; }
 constexpr bool getFalse() { return false; }
 constexpr void* getNull() { return nullptr; }