Implement semantic checking for __builtin_signbit.

r242675 changed the signature for the signbit builtin but did not introduce proper semantic checking to ensure the arguments are as-expected. This patch groups the signbit builtin along with the other fp classification builtins. Fixes PR28172.

llvm-svn: 335050
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 5530bd8..237484a 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -972,6 +972,9 @@
   case Builtin::BI__builtin_isinf_sign:
   case Builtin::BI__builtin_isnan:
   case Builtin::BI__builtin_isnormal:
+  case Builtin::BI__builtin_signbit:
+  case Builtin::BI__builtin_signbitf:
+  case Builtin::BI__builtin_signbitl:
     if (SemaBuiltinFPClassification(TheCall, 1))
       return ExprError();
     break;
@@ -4592,15 +4595,19 @@
                 diag::err_typecheck_call_invalid_unary_fp)
       << OrigArg->getType() << OrigArg->getSourceRange();
 
-  // If this is an implicit conversion from float -> float or double, remove it.
+  // If this is an implicit conversion from float -> float, double, or
+  // long double, remove it.
   if (ImplicitCastExpr *Cast = dyn_cast<ImplicitCastExpr>(OrigArg)) {
     // Only remove standard FloatCasts, leaving other casts inplace
     if (Cast->getCastKind() == CK_FloatingCast) {
       Expr *CastArg = Cast->getSubExpr();
       if (CastArg->getType()->isSpecificBuiltinType(BuiltinType::Float)) {
-          assert((Cast->getType()->isSpecificBuiltinType(BuiltinType::Double) ||
-                  Cast->getType()->isSpecificBuiltinType(BuiltinType::Float)) &&
-               "promotion from float to either float or double is the only expected cast here");
+        assert(
+            (Cast->getType()->isSpecificBuiltinType(BuiltinType::Double) ||
+             Cast->getType()->isSpecificBuiltinType(BuiltinType::Float) ||
+             Cast->getType()->isSpecificBuiltinType(BuiltinType::LongDouble)) &&
+            "promotion from float to either float, double, or long double is "
+            "the only expected cast here");
         Cast->setSubExpr(nullptr);
         TheCall->setArg(NumArgs-1, CastArg);
       }