rustc: Fix x86 ffi for struct arguments

This fixes struct passing abi on x86 ffi: Structs are now passed
indirectly with byval attribute (as clang does).

Author: klutzy

src/librustc/middle/trans/cabi_x86.rs

@@ -62,8 +62,14 @@ pub fn compute_abi_info(ccx: &CrateContext,
         ret_ty = ArgType::direct(rty, None, None, None);
     }
 
-    for &a in atys.iter() {
-        arg_tys.push(ArgType::direct(a, None, None, None));
+    for &t in atys.iter() {
+        let ty = match t.kind() {
+            Struct => {
+                ArgType::indirect(t, Some(ByValAttribute))
+            }
+            _ => ArgType::direct(t, None, None, None),
+        };
+        arg_tys.push(ty);
     }
 
     return FnType {

src/librustc/middle/trans/foreign.rs

@@ -145,14 +145,22 @@ pub fn register_foreign_item_fn(ccx: @CrateContext, abis: AbiSet,
     let llfn;
     {
         let mut externs = ccx.externs.borrow_mut();
-        llfn = base::get_extern_fn(externs.get(),
+        let externs = externs.get();
+        let name = lname.get();
+        let fn_exists = externs.contains_key_equiv(&name);
+        llfn = base::get_extern_fn(externs,
                                    ccx.llmod,
-                                   lname.get(),
+                                   name,
                                    cc,
                                    llfn_ty,
                                    tys.fn_sig.output);
+        if !fn_exists {
+            // if function is already declared before get_extern_fn, it is bad to add attributes
+            // because the declared one may have different signature. (see also #12707)
+            // Add attributes only if they are declared just now.
+            add_argument_attributes(&tys, llfn);
+        }
     };
-    add_argument_attributes(&tys, llfn);
 
     llfn
 }

src/test/run-pass/extern-pass-TwoU16s.rs

@@ -8,12 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// ignore-test #5744 fails on 32 bit
-
 // Test a foreign function that accepts and returns a struct
 // by value.
 
-#[deriving(Eq)]
+#[deriving(Eq, Show)]
 struct TwoU16s {
     one: u16, two: u16
 }

src/test/run-pass/extern-pass-TwoU8s.rs

@@ -8,12 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// ignore-test #5744 fails on 32 bit
-
 // Test a foreign function that accepts and returns a struct
 // by value.
 
-#[deriving(Eq)]
+#[deriving(Eq, Show)]
 struct TwoU8s {
     one: u8, two: u8
 }