Fix integer overflow in rotate_left

src/librustc_mir/interpret/intrinsics.rs

@@ -194,7 +194,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
                 let raw_shift_bits = self.read_scalar(args[1])?.to_bits(layout.size)?;
                 let width_bits = layout.size.bits() as u128;
                 let shift_bits = raw_shift_bits % width_bits;
-                let inv_shift_bits = (width_bits - raw_shift_bits) % width_bits;
+                let inv_shift_bits = (width_bits - shift_bits) % width_bits;
                 let result_bits = if intrinsic_name == "rotate_left" {
                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
                 } else {

src/test/run-pass/const-int-rotate.rs

@@ -1,11 +1,45 @@
 const LEFT: u32 = 0x10000b3u32.rotate_left(8);
 const RIGHT: u32 = 0xb301u32.rotate_right(8);
 
+// Rotating these should make no difference
+//
+// We test using 124 bits because to ensure that overlong bit shifts do
+// not cause undefined behaviour. See #10183.
+const LEFT_OVERFLOW: i16 = 0i16.rotate_left(124);
+const RIGHT_OVERFLOW: i16 = 0i16.rotate_right(124);
+const ONE_LEFT_OVERFLOW: u16 = 1u16.rotate_left(124);
+const ONE_RIGHT_OVERFLOW: u16 = 1u16.rotate_right(124);
+
+const NON_ZERO_LEFT_OVERFLOW: u16 = 0b10u16.rotate_left(124);
+const NON_ZERO_RIGHT_OVERFLOW: u16 = 0b10u16.rotate_right(124);
+
+// Rotating by 0 should have no effect
+const ZERO_ROTATE_LEFT: i8 = 0b0010_0001i8.rotate_left(0);
+const ZERO_ROTATE_RIGHT: i8 = 0b0111_1001i8.rotate_right(0);
+
+// Rotating by a multiple of word size should also have no effect
+const MULTIPLE_ROTATE_LEFT: i32 = 0b0010_0001i32.rotate_left(128);
+const MULTIPLE_ROTATE_RIGHT: i32 = 0b0010_0001i32.rotate_right(128);
+
 fn ident<T>(ident: T) -> T {
     ident
 }
 
 fn main() {
     assert_eq!(LEFT, ident(0xb301));
-    assert_eq!(RIGHT, ident(0x10000b3));
+    assert_eq!(RIGHT, ident(0x0100_00b3));
+
+    assert_eq!(LEFT_OVERFLOW, ident(0));
+    assert_eq!(RIGHT_OVERFLOW, ident(0));
+    assert_eq!(ONE_LEFT_OVERFLOW, ident(0b0001_0000_0000_0000));
+    assert_eq!(ONE_RIGHT_OVERFLOW, ident(0b0001_0000));
+
+    assert_eq!(NON_ZERO_LEFT_OVERFLOW, ident(0b0010_0000_0000_0000));
+    assert_eq!(NON_ZERO_RIGHT_OVERFLOW, ident(0b0000_0000_0010_0000));
+
+    assert_eq!(ZERO_ROTATE_LEFT, ident(0b0010_0001));
+    assert_eq!(ZERO_ROTATE_RIGHT, ident(0b0111_1001));
+
+    assert_eq!(MULTIPLE_ROTATE_LEFT, ident(0b0010_0001));
+    assert_eq!(MULTIPLE_ROTATE_RIGHT, ident(0b0010_0001));
 }