Reinstate r359059, reverted in r359361, with a fix to properly prevent

us emitting the operand of __builtin_constant_p if it has side-effects.

Original commit message:

Fix interactions between __builtin_constant_p and constexpr to match
current trunk GCC.

GCC permits information from outside the operand of
__builtin_constant_p (but in the same constant evaluation context) to be
used within that operand; clang now does so too. A few other minor
deviations from GCC's behavior showed up in my testing and are also
fixed (matching GCC):
  * Clang now supports nullptr_t as the argument type for
    __builtin_constant_p
    * Clang now returns true from __builtin_constant_p if called with a
    null pointer
    * Clang now returns true from __builtin_constant_p if called with an
    integer cast to pointer type

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359367 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index de061e62aa..4c2d1dc768 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -1199,10 +1199,14 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
     if (checkArgCount(*this, TheCall, 1)) return true;
     TheCall->setType(Context.IntTy);
     break;
-  case Builtin::BI__builtin_constant_p:
+  case Builtin::BI__builtin_constant_p: {
     if (checkArgCount(*this, TheCall, 1)) return true;
+    ExprResult Arg = DefaultFunctionArrayLvalueConversion(TheCall->getArg(0));
+    if (Arg.isInvalid()) return true;
+    TheCall->setArg(0, Arg.get());
     TheCall->setType(Context.IntTy);
     break;
+  }
   case Builtin::BI__builtin_launder:
     return SemaBuiltinLaunder(*this, TheCall);
   case Builtin::BI__sync_fetch_and_add: