transpile: In name_reference, also check expression for side effects

Author: Rua

c2rust-transpile/src/translator/mod.rs

@@ -18,11 +18,11 @@ use proc_macro2::{Punct, Spacing::*, Span, TokenStream, TokenTree};
 use syn::spanned::Spanned as _;
 use syn::{
     AttrStyle, BareVariadic, BinOp, Block, Expr, ExprBinary, ExprBlock, ExprBreak, ExprCast,
-    ExprField, ExprIndex, ExprParen, ExprReturn, ExprUnary, FnArg, ForeignItem, ForeignItemFn,
-    ForeignItemMacro, ForeignItemStatic, ForeignItemType, Ident, Item, ItemConst, ItemEnum,
-    ItemExternCrate, ItemFn, ItemForeignMod, ItemImpl, ItemMacro, ItemMod, ItemStatic, ItemStruct,
-    ItemTrait, ItemTraitAlias, ItemType, ItemUnion, ItemUse, Lit, MacroDelimiter, PathSegment,
-    ReturnType, Stmt, Type, TypeTuple, UnOp, UseTree, Visibility,
+    ExprParen, ExprReturn, ExprUnary, FnArg, ForeignItem, ForeignItemFn, ForeignItemMacro,
+    ForeignItemStatic, ForeignItemType, Ident, Item, ItemConst, ItemEnum, ItemExternCrate, ItemFn,
+    ItemForeignMod, ItemImpl, ItemMacro, ItemMod, ItemStatic, ItemStruct, ItemTrait,
+    ItemTraitAlias, ItemType, ItemUnion, ItemUse, Lit, MacroDelimiter, PathSegment, ReturnType,
+    Stmt, Type, TypeTuple, UnOp, UseTree, Visibility,
 };
 
 use crate::diagnostics::TranslationResult;

c2rust-transpile/src/translator/named_references.rs

@@ -18,22 +18,6 @@ fn is_lvalue(e: &Expr) -> bool {
     )
 }
 
-/// Check if something is a side-effect free Rust lvalue.
-fn is_simple_lvalue(e: &Expr) -> bool {
-    use Expr::*;
-    match *unparen(e) {
-        Path(..) => true,
-        Unary(ExprUnary {
-            op: syn::UnOp::Deref(_),
-            ref expr,
-            ..
-        })
-        | Field(ExprField { base: ref expr, .. })
-        | Index(ExprIndex { ref expr, .. }) => is_simple_lvalue(expr),
-        _ => false,
-    }
-}
-
 pub struct NamedReference<R> {
     pub lvalue: Box<Expr>,
     pub rvalue: R,
@@ -106,18 +90,17 @@ impl<'c> Translation<'c> {
             .kind
             .get_qual_type()
             .ok_or_else(|| format_err!("bad reference type"))?;
+
+        let is_pure = self.ast_context.is_expr_pure(reference);
         let read = |write| self.read(reference_ty, write);
         let reference = self.convert_expr(ctx.used(), reference, Some(reference_ty))?;
         reference.and_then_try(|reference| {
-            if !uses_read && is_lvalue(&reference) {
+            if is_lvalue(&reference) && (is_pure || !uses_read) {
+                let rvalue = uses_read.then(|| read(reference.clone())).transpose()?;
+
                 Ok(WithStmts::new_val(NamedReference {
                     lvalue: reference,
-                    rvalue: None,
-                }))
-            } else if is_simple_lvalue(&reference) {
-                Ok(WithStmts::new_val(NamedReference {
-                    lvalue: reference.clone(),
-                    rvalue: Some(read(reference)?),
+                    rvalue,
                 }))
             } else {
                 // This is the case where we explicitly need to factor out possible side-effects.

c2rust-transpile/tests/snapshots/snapshots__transpile@exprs.c.2021.clang15.snap

@@ -62,15 +62,19 @@ pub unsafe extern "C" fn inc_decl_with_rvalue_side_effect() {
     arr[side_effect() as usize] -= 1;
     arr[side_effect() as usize] += 1;
     arr[side_effect() as usize] -= 1;
-    arr[side_effect() as usize] += 1;
-    let mut pre_inc: ::core::ffi::c_int = arr[side_effect() as usize];
-    arr[side_effect() as usize] -= 1;
-    let mut pre_dec: ::core::ffi::c_int = arr[side_effect() as usize];
-    let c2rust_fresh0 = arr[side_effect() as usize];
-    arr[side_effect() as usize] = arr[side_effect() as usize] + 1;
+    let c2rust_lvalue = &raw mut arr[side_effect() as usize];
+    *c2rust_lvalue += 1;
+    let mut pre_inc: ::core::ffi::c_int = *c2rust_lvalue;
+    let c2rust_lvalue_0 = &raw mut arr[side_effect() as usize];
+    *c2rust_lvalue_0 -= 1;
+    let mut pre_dec: ::core::ffi::c_int = *c2rust_lvalue_0;
+    let c2rust_lvalue_1 = &raw mut arr[side_effect() as usize];
+    let c2rust_fresh0 = *c2rust_lvalue_1;
+    *c2rust_lvalue_1 = *c2rust_lvalue_1 + 1;
     let mut post_inc: ::core::ffi::c_int = c2rust_fresh0;
-    let c2rust_fresh1 = arr[side_effect() as usize];
-    arr[side_effect() as usize] = arr[side_effect() as usize] - 1;
+    let c2rust_lvalue_2 = &raw mut arr[side_effect() as usize];
+    let c2rust_fresh1 = *c2rust_lvalue_2;
+    *c2rust_lvalue_2 = *c2rust_lvalue_2 - 1;
     let mut post_dec: ::core::ffi::c_int = c2rust_fresh1;
 }
 #[no_mangle]

c2rust-transpile/tests/snapshots/snapshots__transpile@exprs.c.2024.clang15.snap

@@ -62,16 +62,20 @@ pub unsafe extern "C" fn inc_decl_with_rvalue_side_effect() {
     arr[side_effect() as usize] -= 1;
     arr[side_effect() as usize] += 1;
     arr[side_effect() as usize] -= 1;
-    arr[side_effect() as usize] += 1;
-    let mut pre_inc: ::core::ffi::c_int = arr[side_effect() as usize];
-    arr[side_effect() as usize] -= 1;
-    let mut pre_dec: ::core::ffi::c_int = arr[side_effect() as usize];
-    let c2rust_fresh0 = arr[side_effect() as usize];
-    arr[side_effect() as usize] = arr[side_effect() as usize] + 1;
-    let mut post_inc: ::core::ffi::c_int = c2rust_fresh0;
-    let c2rust_fresh1 = arr[side_effect() as usize];
-    arr[side_effect() as usize] = arr[side_effect() as usize] - 1;
-    let mut post_dec: ::core::ffi::c_int = c2rust_fresh1;
+    let c2rust_lvalue = &raw mut *lvalue_side_effect();
+    *c2rust_lvalue += 1;
+    let mut pre_inc: ::core::ffi::c_int = *c2rust_lvalue;
+    let c2rust_lvalue_0 = &raw mut *lvalue_side_effect();
+    *c2rust_lvalue_0 -= 1;
+    let mut pre_dec: ::core::ffi::c_int = *c2rust_lvalue_0;
+    let c2rust_lvalue_1 = &raw mut *lvalue_side_effect();
+    let c2rust_fresh2 = *c2rust_lvalue_1;
+    *c2rust_lvalue_1 = *c2rust_lvalue_1 + 1;
+    let mut post_inc: ::core::ffi::c_int = c2rust_fresh2;
+    let c2rust_lvalue_2 = &raw mut *lvalue_side_effect();
+    let c2rust_fresh3 = *c2rust_lvalue_2;
+    *c2rust_lvalue_2 = *c2rust_lvalue_2 - 1;
+    let mut post_dec: ::core::ffi::c_int = c2rust_fresh3;
 }
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn inc_decl_with_lvalue_side_effect() {
@@ -86,13 +90,13 @@ pub unsafe extern "C" fn inc_decl_with_lvalue_side_effect() {
     *c2rust_lvalue_0 -= 1;
     let mut pre_dec: ::core::ffi::c_int = *c2rust_lvalue_0;
     let c2rust_lvalue_1 = &raw mut *lvalue_side_effect();
-    let c2rust_fresh2 = *c2rust_lvalue_1;
+    let c2rust_lvalue_1 = *c2rust_lvalue_1;
     *c2rust_lvalue_1 = *c2rust_lvalue_1 + 1;
-    let mut post_inc: ::core::ffi::c_int = c2rust_fresh2;
+    let mut post_inc: ::core::ffi::c_int = c2rust_lvalue_1;
     let c2rust_lvalue_2 = &raw mut *lvalue_side_effect();
-    let c2rust_fresh3 = *c2rust_lvalue_2;
+    let c2rust_fresh2 = *c2rust_lvalue_2;
     *c2rust_lvalue_2 = *c2rust_lvalue_2 - 1;
-    let mut post_dec: ::core::ffi::c_int = c2rust_fresh3;
+    let mut post_dec: ::core::ffi::c_int = c2rust_fresh2;
 }
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn unsigned_compound_desugaring() {