only allow side effect in unary expr when argument expr is not pure

Author: bungcip

c2rust-transpile/src/translator/operators.rs

@@ -1034,9 +1034,9 @@ 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 arg expr is not pure
+        if ctx.is_unused() && !self.ast_context.is_expr_pure(arg) {
             let v = unary.clone().into_value();
             unary
                 .stmts_mut()

c2rust-transpile/tests/snapshots/exprs.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+void increment(){
+    int i = 5;
+    i++;
+    i--;
+    --i;
+    ++i;
+}
+
+int side_effect(){
+    printf("tuturu.. i am side effect");
+    return 10;
+}
+
+void unary(){
+    -side_effect();
+    +side_effect();
+    ~side_effect();
+    !side_effect();
+    &side_effect;
+    *side_effect; 
+}

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

@@ -0,0 +1,37 @@
+---
+source: c2rust-transpile/tests/snapshots.rs
+expression: cat tests/snapshots/exprs.rs
+input_file: c2rust-transpile/tests/snapshots/exprs.c
+---
+#![allow(
+    dead_code,
+    mutable_transmutes,
+    non_camel_case_types,
+    non_snake_case,
+    non_upper_case_globals,
+    unused_assignments,
+    unused_mut
+)]
+extern "C" {
+    fn printf(__format: *const std::ffi::c_char, ...) -> std::ffi::c_int;
+}
+#[no_mangle]
+pub unsafe extern "C" fn increment() {
+    let mut i: std::ffi::c_int = 5 as std::ffi::c_int;
+    i += 1;
+    i -= 1;
+    i -= 1;
+    i += 1;
+}
+#[no_mangle]
+pub unsafe extern "C" fn side_effect() -> std::ffi::c_int {
+    printf(b"tuturu.. i am side effect\0" as *const u8 as *const std::ffi::c_char);
+    return 10 as std::ffi::c_int;
+}
+#[no_mangle]
+pub unsafe extern "C" fn unary() {
+    -side_effect();
+    side_effect();
+    !side_effect();
+    (side_effect() == 0) as std::ffi::c_int;
+}

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]

@@ -406,13 +406,10 @@ pub unsafe extern "C" fn stmt_expr_inc() -> std::ffi::c_int {
     let mut b: *mut std::ffi::c_int = &mut a;
     ({
         *b += 1;
-        *b;
-        *b;
         *b
     });
     return ({
         *b += 1;
-        *b;
         *b
     });
 }