trans: update Luqmana's patch for generalized pair handling.

Author: eddyb

Diff for: src/librustc_trans/mir/block.rs

@@ -852,63 +852,74 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
                     op: OperandRef<'tcx>) {
         use self::ReturnDest::*;
 
-        match dest {
-            Nothing => (),
+        // Handle the simple cases that don't require casts, first.
+        let llcast_ty = match dest {
+            Nothing => return,
             Store(dst) => {
                 if let Some(llcast_ty) = ret_ty.cast {
-                    let ccx = bcx.ccx();
-                    // The actual return type is a struct, but the ABI
-                    // adaptation code has cast it into some scalar type.  The
-                    // code that follows is the only reliable way I have
-                    // found to do a transform like i64 -> {i32,i32}.
-                    // Basically we dump the data onto the stack then memcpy it.
-                    //
-                    // Other approaches I tried:
-                    // - Casting rust ret pointer to the foreign type and using Store
-                    //   is (a) unsafe if size of foreign type > size of rust type and
-                    //   (b) runs afoul of strict aliasing rules, yielding invalid
-                    //   assembly under -O (specifically, the store gets removed).
-                    // - Truncating foreign type to correct integral type and then
-                    //   bitcasting to the struct type yields invalid cast errors.
-
-                    // We instead thus allocate some scratch space...
-                    let llscratch = bcx.alloca(llcast_ty, "fn_ret_cast");
-                    bcx.with_block(|bcx| base::call_lifetime_start(bcx, llscratch));
-
-                    // ...where we first store the value...
-                    bcx.store(op.immediate(), llscratch);
-
-                    // ...and then memcpy it to the intended destination.
-                    base::call_memcpy(bcx,
-                                      bcx.pointercast(dst, Type::i8p(ccx)),
-                                      bcx.pointercast(llscratch, Type::i8p(ccx)),
-                                      C_uint(ccx, llsize_of_store(ccx, ret_ty.original_ty)),
-                                      cmp::min(llalign_of_min(ccx, ret_ty.original_ty),
-                                               llalign_of_min(ccx, llcast_ty)) as u32);
-
-                    bcx.with_block(|bcx| base::call_lifetime_end(bcx, llscratch));
+                    llcast_ty
                 } else {
                     ret_ty.store(bcx, op.immediate(), dst);
+                    return;
                 }
             }
             IndirectOperand(tmp, idx) => {
                 let op = self.trans_load(bcx, tmp, op.ty);
                 self.temps[idx as usize] = TempRef::Operand(Some(op));
+                return;
             }
             DirectOperand(idx) => {
-                // If there is a cast, we have to store and reload.
-                let op = if ret_ty.cast.is_some() {
-                    let tmp = bcx.with_block(|bcx| {
-                        base::alloc_ty(bcx, op.ty, "tmp_ret")
-                    });
-                    ret_ty.store(bcx, op.immediate(), tmp);
-                    self.trans_load(bcx, tmp, op.ty)
+                if let Some(llcast_ty) = ret_ty.cast {
+                    llcast_ty
                 } else {
-                    op.unpack_if_pair(bcx)
-                };
+                    let op = op.unpack_if_pair(bcx);
+                    self.temps[idx as usize] = TempRef::Operand(Some(op));
+                    return;
+                }
+            }
+        };
+
+        // The actual return type is a struct, but the ABI
+        // adaptation code has cast it into some scalar type.  The
+        // code that follows is the only reliable way I have
+        // found to do a transform like i64 -> {i32,i32}.
+        // Basically we dump the data onto the stack then memcpy it.
+        //
+        // Other approaches I tried:
+        // - Casting rust ret pointer to the foreign type and using Store
+        //   is (a) unsafe if size of foreign type > size of rust type and
+        //   (b) runs afoul of strict aliasing rules, yielding invalid
+        //   assembly under -O (specifically, the store gets removed).
+        // - Truncating foreign type to correct integral type and then
+        //   bitcasting to the struct type yields invalid cast errors.
+
+        // We instead thus allocate some scratch space...
+        let llscratch = bcx.alloca(llcast_ty, "fn_ret_cast");
+        bcx.with_block(|bcx| base::call_lifetime_start(bcx, llscratch));
+
+        // ...where we first store the value...
+        bcx.store(op.immediate(), llscratch);
+
+        let ccx = bcx.ccx();
+        match dest {
+            Store(dst) => {
+                // ...and then memcpy it to the intended destination.
+                base::call_memcpy(bcx,
+                                  bcx.pointercast(dst, Type::i8p(ccx)),
+                                  bcx.pointercast(llscratch, Type::i8p(ccx)),
+                                  C_uint(ccx, llsize_of_store(ccx, ret_ty.original_ty)),
+                                  cmp::min(llalign_of_min(ccx, ret_ty.original_ty),
+                                           llalign_of_min(ccx, llcast_ty)) as u32);
+            }
+            DirectOperand(idx) => {
+                let llptr = bcx.pointercast(llscratch, ret_ty.original_ty.ptr_to());
+                let op = self.trans_load(bcx, llptr, op.ty);
                 self.temps[idx as usize] = TempRef::Operand(Some(op));
             }
+            Nothing | IndirectOperand(_, _) => bug!()
         }
+
+        bcx.with_block(|bcx| base::call_lifetime_end(bcx, llscratch));
     }
 }
 

Diff for: src/test/run-pass/mir_cast_fn_ret.rs

@@ -10,15 +10,25 @@
 
 #![feature(rustc_attrs)]
 
-pub extern "C" fn foo() -> (u8, u8, u8) {
+pub extern "C" fn tuple2() -> (u16, u8) {
+    (1, 2)
+}
+
+pub extern "C" fn tuple3() -> (u8, u8, u8) {
     (1, 2, 3)
 }
 
 #[rustc_mir]
-pub fn bar() -> u8 {
-    foo().2
+pub fn test2() -> u8 {
+    tuple2().1
+}
+
+#[rustc_mir]
+pub fn test3() -> u8 {
+    tuple3().2
 }
 
 fn main() {
-    assert_eq!(bar(), 3);
+    assert_eq!(test2(), 2);
+    assert_eq!(test3(), 3);
 }