don't add unused statement in increment/decrement operator

Author: bungcip

c2rust-transpile/src/translator/operators.rs

@@ -1034,13 +1034,19 @@ impl<'c> Translation<'c> {
             }
         }?;
 
-        // Unused unary operators (`-foo()`) may have side effects, so we need
-        // to add them to stmts.
-        if ctx.is_unused() {
+        // Some unused unary operators (`-foo()`) may have side effects, so we need
+        // to add them to stmts when name is not increment/decrement operator.
+        if ctx.is_unused()
+            && !matches!(
+                name,
+                c_ast::UnOp::PreDecrement
+                    | c_ast::UnOp::PreIncrement
+                    | c_ast::UnOp::PostDecrement
+                    | c_ast::UnOp::PostIncrement
+            )
+        {
             let v = unary.clone().into_value();
-            unary
-                .stmts_mut()
-                .push(Stmt::Expr(*v, Some(Default::default())));
+            unary.add_stmt(mk().semi_stmt(v));
         }
         Ok(unary)
     }

c2rust-transpile/tests/snapshots/[email protected]

@@ -29,13 +29,9 @@ pub unsafe extern "C" fn unary_without_side_effect() {
     &mut i;
     i;
     i += 1;
-    i;
     i -= 1;
-    i;
     i -= 1;
-    i;
     i += 1;
-    i;
 }
 #[no_mangle]
 pub unsafe extern "C" fn unary_with_side_effect() {
@@ -50,11 +46,7 @@ pub unsafe extern "C" fn unary_with_side_effect() {
     >(side_effect)() as isize) as *const std::ffi::c_char;
     *arr[side_effect() as usize];
     arr[side_effect() as usize] = (arr[side_effect() as usize]).offset(1);
-    arr[side_effect() as usize];
     arr[side_effect() as usize] = (arr[side_effect() as usize]).offset(-1);
-    arr[side_effect() as usize];
     arr[side_effect() as usize] = (arr[side_effect() as usize]).offset(1);
-    arr[side_effect() as usize];
     arr[side_effect() as usize] = (arr[side_effect() as usize]).offset(-1);
-    arr[side_effect() as usize];
 }

c2rust-transpile/tests/snapshots/[email protected]

@@ -19,7 +19,6 @@ pub unsafe extern "C" fn factorial(mut n: std::ffi::c_ushort) -> std::ffi::c_ush
     while (i as std::ffi::c_int) < n as std::ffi::c_int {
         result = (result as std::ffi::c_int * i as std::ffi::c_int) as std::ffi::c_ushort;
         i = i.wrapping_add(1);
-        i;
     }
     return result;
 }

c2rust-transpile/tests/snapshots/[email protected]

@@ -1,6 +1,5 @@
 ---
 source: c2rust-transpile/tests/snapshots.rs
-assertion_line: 67
 expression: cat tests/snapshots/gotos.rs
 input_file: c2rust-transpile/tests/snapshots/gotos.c
 ---
@@ -19,8 +18,6 @@ pub unsafe extern "C" fn sum(mut count: std::ffi::c_int) -> std::ffi::c_int {
     while !(count <= 0 as std::ffi::c_int) {
         x += count;
         count -= 1;
-        count;
     }
     return x;
 }
-

c2rust-transpile/tests/snapshots/[email protected]

@@ -21,10 +21,8 @@ pub unsafe extern "C" fn insertion_sort(n: std::ffi::c_int, p: *mut std::ffi::c_
         while j > 0 as std::ffi::c_int && *p.offset((j - 1 as std::ffi::c_int) as isize) > tmp {
             *p.offset(j as isize) = *p.offset((j - 1 as std::ffi::c_int) as isize);
             j -= 1;
-            j;
         }
         *p.offset(j as isize) = tmp;
         i += 1;
-        i;
     }
 }

c2rust-transpile/tests/snapshots/[email protected]

@@ -407,12 +407,10 @@ pub unsafe extern "C" fn stmt_expr_inc() -> std::ffi::c_int {
     ({
         *b += 1;
         *b;
-        *b;
         *b
     });
     return ({
         *b += 1;
-        *b;
         *b
     });
 }