Ensure llvm doesn't trigger an assert for crazy transmutes

Author: oli-obk

src/librustc_codegen_llvm/mir/constant.rs

@@ -70,11 +70,8 @@ pub fn scalar_to_llvm(cx: &CodegenCx,
                 &C_usize(cx, ptr.offset.bytes()),
                 1,
             ) };
-            if layout.value != layout::Pointer {
-                unsafe { llvm::LLVMConstPtrToInt(llval, llty.to_ref()) }
-            } else {
-                consts::bitcast(llval, llty)
-            }
+            let llval = unsafe { llvm::LLVMConstPtrToInt(llval, llty.to_ref()) };
+            consts::bitcast(llval, llty)
         }
     }
 }

src/test/ui/const-eval/ref_to_float_transmute.rs

@@ -0,0 +1,28 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//compile-pass
+
+fn main() {}
+
+static FOO: u32 = 42;
+
+union Foo {
+    f: Float,
+    r: &'static u32,
+}
+
+#[cfg(target_pointer_width="64")]
+type Float = f64;
+
+#[cfg(target_pointer_width="32")]
+type Float = f32;
+
+static BAR: Float = unsafe { Foo { r: &FOO }.f };