auto merge of #14121 : luqmana/rust/option-ffi, r=alexcrichton

This slightly adjusts the NullablePointer representation for some enums in the case where the non-nullable variant has a single field (the ptr field) to be just that, the pointer. This is in contrast to the current behaviour where we'd wrap that single pointer in a LLVM struct.

Fixes #11040 & #11303.

src/test/debuginfo/option-like-enum.rs

@@ -16,10 +16,10 @@
 // gdb-command:finish
 
 // gdb-command:print some
-// gdb-check:$1 = {0x12345678}
+// gdb-check:$1 = (u32 *) 0x12345678
 
 // gdb-command:print none
-// gdb-check:$2 = {0x0}
+// gdb-check:$2 = (u32 *) 0x0
 
 // gdb-command:print full
 // gdb-check:$3 = {454545, 0x87654321, 9988}
@@ -41,6 +41,8 @@
 // contains a non-nullable pointer, then this value is used as the discriminator.
 // The test cases in this file make sure that something readable is generated for
 // this kind of types.
+// If the non-empty variant contains a single non-nullable pointer than the whole
+// item is represented as just a pointer and not wrapped in a struct.
 // Unfortunately (for these test cases) the content of the non-discriminant fields
 // in the null-case is not defined. So we just read the discriminator field in
 // this case (by casting the value to a memory-equivalent struct).

src/test/debuginfo/recursive-struct.rs

@@ -20,53 +20,53 @@
 
 // gdb-command:print stack_unique.value
 // gdb-check:$1 = 0
-// gdb-command:print stack_unique.next.val->value
+// gdb-command:print stack_unique.next->value
 // gdb-check:$2 = 1
 
 // gdb-command:print unique_unique->value
 // gdb-check:$3 = 2
-// gdb-command:print unique_unique->next.val->value
+// gdb-command:print unique_unique->next->value
 // gdb-check:$4 = 3
 
 // gdb-command:print box_unique->val.value
 // gdb-check:$5 = 4
-// gdb-command:print box_unique->val.next.val->value
+// gdb-command:print box_unique->val.next->value
 // gdb-check:$6 = 5
 
 // gdb-command:print vec_unique[0].value
 // gdb-check:$7 = 6.5
-// gdb-command:print vec_unique[0].next.val->value
+// gdb-command:print vec_unique[0].next->value
 // gdb-check:$8 = 7.5
 
 // gdb-command:print borrowed_unique->value
 // gdb-check:$9 = 8.5
-// gdb-command:print borrowed_unique->next.val->value
+// gdb-command:print borrowed_unique->next->value
 // gdb-check:$10 = 9.5
 
 // MANAGED
 // gdb-command:print stack_managed.value
 // gdb-check:$11 = 10
-// gdb-command:print stack_managed.next.val->val.value
+// gdb-command:print stack_managed.next.val->value
 // gdb-check:$12 = 11
 
 // gdb-command:print unique_managed->value
 // gdb-check:$13 = 12
-// gdb-command:print unique_managed->next.val->val.value
+// gdb-command:print unique_managed->next.val->value
 // gdb-check:$14 = 13
 
-// gdb-command:print box_managed->val.value
+// gdb-command:print box_managed.val->value
 // gdb-check:$15 = 14
-// gdb-command:print box_managed->val.next.val->val.value
+// gdb-command:print box_managed->val->next.val->value
 // gdb-check:$16 = 15
 
 // gdb-command:print vec_managed[0].value
 // gdb-check:$17 = 16.5
-// gdb-command:print vec_managed[0].next.val->val.value
+// gdb-command:print vec_managed[0].next.val->value
 // gdb-check:$18 = 17.5
 
 // gdb-command:print borrowed_managed->value
 // gdb-check:$19 = 18.5
-// gdb-command:print borrowed_managed->next.val->val.value
+// gdb-command:print borrowed_managed->next.val->value
 // gdb-check:$20 = 19.5
 
 // LONG CYCLE
@@ -97,7 +97,7 @@
 // gdb-command:print (*****long_cycle_w_anonymous_types).value
 // gdb-check:$31 = 30
 
-// gdb-command:print (*****((*****long_cycle_w_anonymous_types).next.val)).value
+// gdb-command:print (*****((*****long_cycle_w_anonymous_types).next)).value
 // gdb-check:$32 = 31
 
 // gdb-command:continue

src/test/run-pass/nullable-pointer-ffi-compat.rs

@@ -0,0 +1,35 @@
+// 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.
+
+// #11303, #11040:
+// This would previously crash on i686 linux due to abi differences
+// between returning an Option<T> and T, where T is a non nullable
+// pointer.
+// If we have an enum with two variants such that one is zero sized
+// and the other contains a nonnullable pointer, we don't use a
+// separate discriminant. Instead we use that pointer field to differentiate
+// between the 2 cases.
+// Also, if the variant with the nonnullable pointer has no other fields
+// then we simply express the enum as just a pointer and not wrap it
+// in a struct.
+
+use std::mem;
+
+#[inline(never)]
+extern "C" fn foo<'a>(x: &'a int) -> Option<&'a int> { Some(x) }
+
+static FOO: int = 0xDEADBEE;
+
+pub fn main() {
+    unsafe {
+        let f: extern "C" fn<'a>(&'a int) -> &'a int = mem::transmute(foo);
+        assert_eq!(*f(&FOO), FOO);
+    }
+}