Fix iabs and add some more tests

src/libcompiler_builtins/lib.rs

@@ -469,16 +469,25 @@ pub mod reimpls {
     }
 
     trait AbsExt: Sized {
-        fn uabs(self) -> u128_;
-        fn iabs(self) -> i128_;
-    }
-
-    impl AbsExt for i128_ {
         fn uabs(self) -> u128_ {
             self.iabs() as u128_
         }
+        fn iabs(self) -> i128_;
+    }
+
+    #[cfg(stage0)]
+    impl AbsExt for i128_ {
         fn iabs(self) -> i128_ {
-            ((self ^ self).wrapping_sub(self))
+            let s = self >> 63;
+            ((self ^ s).wrapping_sub(s))
+        }
+    }
+
+    #[cfg(not(stage0))]
+    impl AbsExt for i128_ {
+        fn iabs(self) -> i128_ {
+            let s = self >> 127;
+            ((self ^ s).wrapping_sub(s))
         }
     }
 

src/test/run-pass/i128.rs

@@ -91,5 +91,9 @@ fn main() {
                format!("{:b}", j));
     assert_eq!("-147573952589676412928", format!("{:?}", j));
     // common traits
-    x.clone();
+    assert_eq!(x, b(x.clone()));
+    // overflow checks
+    assert_eq!((-z).checked_mul(-z), Some(0x734C_C2F2_A521));
+    assert_eq!((z).checked_mul(z), Some(0x734C_C2F2_A521));
+    assert_eq!((k).checked_mul(k), None);
 }