Revert "Remove the return_address intrinsic."

This reverts commit b30134d.

Author: eddyb

src/libcore/intrinsics.rs

@@ -293,6 +293,12 @@ extern "rust-intrinsic" {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn transmute<T, U>(e: T) -> U;
 
+    /// Gives the address for the return value of the enclosing function.
+    ///
+    /// Using this intrinsic in a function that does not use an out pointer
+    /// will trigger a compiler error.
+    pub fn return_address() -> *const u8;
+
     /// Returns `true` if the actual type given as `T` requires drop
     /// glue; returns `false` if the actual type provided for `T`
     /// implements `Copy`.

src/librustc_trans/diagnostics.rs

@@ -12,6 +12,44 @@
 
 register_long_diagnostics! {
 
+E0510: r##"
+`return_address` was used in an invalid context. Erroneous code example:
+
+```ignore
+#![feature(intrinsics)]
+
+extern "rust-intrinsic" {
+    fn return_address() -> *const u8;
+}
+
+unsafe fn by_value() -> i32 {
+    let _ = return_address();
+    // error: invalid use of `return_address` intrinsic: function does
+    //        not use out pointer
+    0
+}
+```
+
+Return values may be stored in a return register(s) or written into a so-called
+out pointer. In case the returned value is too big (this is
+target-ABI-dependent and generally not portable or future proof) to fit into
+the return register(s), the compiler will return the value by writing it into
+space allocated in the caller's stack frame. Example:
+
+```
+#![feature(intrinsics)]
+
+extern "rust-intrinsic" {
+    fn return_address() -> *const u8;
+}
+
+unsafe fn by_pointer() -> String {
+    let _ = return_address();
+    String::new() // ok!
+}
+```
+"##,
+
 E0511: r##"
 Invalid monomorphization of an intrinsic function was used. Erroneous code
 example:

src/librustc_trans/intrinsic.rs

@@ -617,6 +617,18 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
 
         },
 
+
+        (_, "return_address") => {
+            if !fcx.fn_ty.ret.is_indirect() {
+                span_err!(tcx.sess, span, E0510,
+                          "invalid use of `return_address` intrinsic: function \
+                           does not use out pointer");
+                C_null(Type::i8p(ccx))
+            } else {
+                PointerCast(bcx, llvm::get_param(fcx.llfn, 0), Type::i8p(ccx))
+            }
+        }
+
         (_, "discriminant_value") => {
             let val_ty = substs.types.get(FnSpace, 0);
             match val_ty.sty {

src/librustc_typeck/check/intrinsic.rs

@@ -275,6 +275,8 @@ pub fn check_intrinsic_type(ccx: &CrateCtxt, it: &hir::ForeignItem) {
             "fadd_fast" | "fsub_fast" | "fmul_fast" | "fdiv_fast" | "frem_fast" =>
                 (1, vec![param(ccx, 0), param(ccx, 0)], param(ccx, 0)),
 
+            "return_address" => (0, vec![], tcx.mk_imm_ptr(tcx.types.u8)),
+
             "assume" => (0, vec![tcx.types.bool], tcx.mk_nil()),
 
             "discriminant_value" => (1, vec![

src/test/compile-fail/intrinsic-return-address.rs

@@ -0,0 +1,24 @@
+// Copyright 2014 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.
+
+#![allow(warnings)]
+#![feature(intrinsics)]
+
+extern "rust-intrinsic" {
+    fn return_address() -> *const u8;
+}
+
+unsafe fn f() { let _ = return_address(); }
+//~^ ERROR invalid use of `return_address` intrinsic: function does not use out pointer
+
+unsafe fn g() -> isize { let _ = return_address(); 0 }
+//~^ ERROR invalid use of `return_address` intrinsic: function does not use out pointer
+
+fn main() {}

src/test/run-pass/intrinsic-return-address.rs

@@ -0,0 +1,43 @@
+// Copyright 2012-2014 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.
+
+
+#![feature(intrinsics)]
+
+use std::ptr;
+
+struct Point {
+    x: f32,
+    y: f32,
+    z: f32,
+}
+
+extern "rust-intrinsic" {
+    fn return_address() -> *const u8;
+}
+
+fn f(result: &mut usize) -> Point {
+    unsafe {
+        *result = return_address() as usize;
+        Point {
+            x: 1.0,
+            y: 2.0,
+            z: 3.0,
+        }
+    }
+
+}
+
+fn main() {
+    let mut intrinsic_reported_address = 0;
+    let pt = f(&mut intrinsic_reported_address);
+    let actual_address = &pt as *const Point as usize;
+    assert_eq!(intrinsic_reported_address, actual_address);
+}