make C-like enums immediate

This fixes two existing bugs along the way:

* The `transmute` intrinsic did not correctly handle casts of immediate
  aggregates like newtype structs and tuples.
* The code for calling foreign functions used the wrong type to create
  an `alloca` temporary

    enum Foo { A, B }
    fn foo() -> Foo { A }

Before:

    ; Function Attrs: nounwind uwtable
    define void @_ZN3foo18hbedc642d5d9cf5aag4v0.0E(%enum.Foo* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      %2 = getelementptr inbounds %enum.Foo* %0, i64 0, i32 0
      store i64 0, i64* %2, align 8
      ret void
    }

After:

    ; Function Attrs: nounwind readnone uwtable
    define %enum.Foo @_ZN3foo18hbedc642d5d9cf5aag4v0.0E({ i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      ret %enum.Foo zeroinitializer
    }

Author: thestinger

src/librustc/middle/trans/common.rs

@@ -69,10 +69,6 @@ pub fn type_is_immediate(ccx: &mut CrateContext, ty: ty::t) -> bool {
     if simple {
         return true;
     }
-    // FIXME: #9651: C-like enums should also be immediate
-    if ty::type_is_c_like_enum(ccx.tcx, ty) {
-        return false;
-    }
     match ty::get(ty).sty {
         // FIXME: #9651: small `ty_struct` should also be immediate
         ty::ty_struct(def_id, ref substs) => {

src/librustc/middle/trans/expr.rs

@@ -1727,7 +1727,9 @@ fn trans_imm_cast(bcx: @mut Block, expr: &ast::Expr,
             (cast_enum, cast_float) => {
                 let bcx = bcx;
                 let repr = adt::represent_type(ccx, t_in);
-                let lldiscrim_a = adt::trans_get_discr(bcx, repr, llexpr);
+                let slot = Alloca(bcx, ll_t_in, "");
+                Store(bcx, llexpr, slot);
+                let lldiscrim_a = adt::trans_get_discr(bcx, repr, slot);
                 match k_out {
                     cast_integral => int_cast(bcx, ll_t_out,
                                               val_ty(lldiscrim_a),

src/librustc/middle/trans/foreign.rs

@@ -222,7 +222,7 @@ pub fn trans_native_call(bcx: @mut Block,
         // Ensure that we always have the Rust value indirectly,
         // because it makes bitcasting easier.
         if !rust_indirect {
-            let scratch = base::alloca(bcx, arg_tys[i].ty, "__arg");
+            let scratch = base::alloca(bcx, type_of::type_of(ccx, fn_sig.inputs[i]), "__arg");
             Store(bcx, llarg_rust, scratch);
             llarg_rust = scratch;
         }

src/librustc/middle/trans/intrinsic.rs

@@ -12,7 +12,7 @@
 
 use back::{abi};
 use lib::llvm::{SequentiallyConsistent, Acquire, Release, Xchg};
-use lib::llvm::{ValueRef, Pointer};
+use lib::llvm::{ValueRef, Pointer, Array, Struct};
 use lib;
 use middle::trans::base::*;
 use middle::trans::build::*;
@@ -333,8 +333,12 @@ pub fn trans_intrinsic(ccx: @mut CrateContext,
                             (Pointer, other) | (other, Pointer) if other != Pointer => {
                                 let tmp = Alloca(bcx, llouttype, "");
                                 Store(bcx, llsrcval, PointerCast(bcx, tmp, llintype.ptr_to()));
-                                let ll_load = Load(bcx, tmp);
-                                Ret(bcx, ll_load);
+                                Ret(bcx, Load(bcx, tmp));
+                            }
+                            (Array, _) | (_, Array) | (Struct, _) | (_, Struct) => {
+                                let tmp = Alloca(bcx, llouttype, "");
+                                Store(bcx, llsrcval, PointerCast(bcx, tmp, llintype.ptr_to()));
+                                Ret(bcx, Load(bcx, tmp));
                             }
                             _ => {
                                 let llbitcast = BitCast(bcx, llsrcval, llouttype);