Handle ::from for unsigned inputs

Author: tbaederr

clang/lib/AST/Interp/IntegralAP.h

@@ -82,8 +82,7 @@ template <bool Signed> class IntegralAP final {
 
   template <unsigned Bits, bool InputSigned>
   static IntegralAP from(Integral<Bits, InputSigned> I) {
-    assert(InputSigned);
-    /// FIXME: Take bits parameter.
+    // FIXME: Take bits parameter.
     APSInt Copy =
         APSInt(APInt(128, static_cast<int64_t>(I), InputSigned), !Signed);
     Copy.setIsSigned(Signed);

clang/test/AST/Interp/literals.cpp

@@ -48,6 +48,8 @@ namespace i128 {
                                          // expected-note {{outside the range}} \
                                          // ref-error {{must be initialized by a constant expression}} \
                                          // ref-note {{outside the range}}
+  constexpr int128_t Two = (int128_t)1 << 1ul;
+  static_assert(Two == 2, "");
 }
 
 constexpr bool b = number;