Skip to content

transpile: Refactor, document and correct uses of used() flag #1975

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
Rua wants to merge 11 commits into
base: master
Choose a base branch
from
Open

transpile: Refactor, document and correct uses of used() flag #1975

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
11 commits
Select commit Hold shift + click to select a range
6c1fa6c
transpile: Split off `side_effects.c` snapshot test
Rua Sep 2, 2026
c4e21f6
transpile: Add more tests to `side_effects.c`
Rua Sep 2, 2026
606309f
transpile: Rename `ExprContext::used` to `is_used` and document it
Rua Aug 15, 2026
7c954b6
transpile: Replace `ExprContext::is_used` and `is_unused` with direct…
Rua Aug 15, 2026
878ca4a
transpile: Pass `used()` for conditions of control flow
Rua Aug 16, 2026
dbc4957
transpile: Pass `used()` for variable initializers
Rua Aug 16, 2026
744f761
transpile: Pass `used()` correctly for assignment operands
Rua Aug 16, 2026
35b1dd8
transpile: Handle `__builtin_bzero` side effects
Rua Sep 2, 2026
e48d158
transpile: Set `is_used` to `false` by default at the top level
Rua Aug 16, 2026
300e4cd
transpile: Shortcut compound literal also if unused
Rua Aug 21, 2026
6dcf1fd
transpile: Remove `used()` for children of pure expressions
Rua Sep 5, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 4 additions & 4 deletions c2rust-transpile/src/cfg/mod.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1491,7 +1491,7 @@ impl CfgBuilder {

// Condition
let (stmts, val) = translator
.convert_condition(ctx, true, scrutinee)?
.convert_condition(ctx.used(), true, scrutinee)?
.discard_unsafe();
wip.extend(stmts);

Expand Down Expand Up @@ -1564,7 +1564,7 @@ impl CfgBuilder {

// Condition
let (stmts, val) = translator
.convert_condition(ctx, true, condition)?
.convert_condition(ctx.used(), true, condition)?
.discard_unsafe();
let cond_val = translator
.ast_context
Expand Down Expand Up @@ -1643,7 +1643,7 @@ impl CfgBuilder {

// Condition
let (stmts, val) = translator
.convert_condition(ctx, true, condition)?
.convert_condition(ctx.used(), true, condition)?
.discard_unsafe();
let cond_val = translator
.ast_context
Expand Down Expand Up @@ -1698,7 +1698,7 @@ impl CfgBuilder {
// Condition
if let Some(cond) = condition {
let (stmts, val) = translator
.convert_condition(ctx, true, cond)?
.convert_condition(ctx.used(), true, cond)?
.discard_unsafe();
let cond_val = translator
.ast_context
Expand Down
51 changes: 26 additions & 25 deletions c2rust-transpile/src/translator/builtins.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -33,16 +33,12 @@ impl<'c> Translation<'c> {
rotate_method_name: &'static str,
) -> TranslationResult<WithStmts<Box<Expr>>> {
// Emit `arg0.{method_name}(arg1)`
let arg0 = self.convert_expr(ctx.used(), args[0], None)?;
let arg1 = self.convert_expr(ctx.used(), args[1], None)?;
let arg0 = self.convert_expr(ctx, args[0], None)?;
let arg1 = self.convert_expr(ctx, args[1], None)?;
Ok(arg0.zip(arg1).and_then(|(arg0, arg1)| {
let arg1 = mk().cast_expr(arg1, mk().path_ty(vec!["u32"]));
let method_call_expr = mk().method_call_expr(arg0, rotate_method_name, vec![arg1]);
self.convert_side_effects_expr(
ctx,
WithStmts::new_val(method_call_expr),
"Builtin is not supposed to be used",
)
WithStmts::new_val(method_call_expr)
}))
}

Expand Down Expand Up @@ -116,15 +112,15 @@ impl<'c> Translation<'c> {
"__builtin_signbit" | "__builtin_signbitf" | "__builtin_signbitl" => {
self.import_num_traits(args[0])?;

let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|v| {
let val = mk().method_call_expr(v, "is_sign_negative", vec![]);

mk().cast_expr(val, mk().abs_path_ty(vec!["core", "ffi", "c_int"]))
}))
}
"__builtin_ffs" | "__builtin_ffsl" | "__builtin_ffsll" => {
let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;

Ok(val.map(|x| {
let add = BinOp::Add(Default::default());
Expand All @@ -141,33 +137,33 @@ impl<'c> Translation<'c> {
}))
}
"__builtin_clz" | "__builtin_clzl" | "__builtin_clzll" => {
let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|x| {
let zeros = mk().method_call_expr(x, "leading_zeros", vec![]);
mk().cast_expr(zeros, mk().path_ty(vec!["i32"]))
}))
}
"__builtin_ctz" | "__builtin_ctzl" | "__builtin_ctzll" => {
let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|x| {
let zeros = mk().method_call_expr(x, "trailing_zeros", vec![]);
mk().cast_expr(zeros, mk().path_ty(vec!["i32"]))
}))
}
"__builtin_bswap16" | "__builtin_bswap32" | "__builtin_bswap64" => {
let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|x| mk().method_call_expr(x, "swap_bytes", vec![])))
}
"__builtin_fabs" | "__builtin_fabsf" | "__builtin_fabsl" => {
self.import_num_traits(args[0])?;

let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|x| mk().method_call_expr(x, "abs", vec![])))
}
"__builtin_isfinite" | "__builtin_isnan" => {
self.import_num_traits(args[0])?;

let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;

let seg = match builtin_name {
"__builtin_isfinite" => "is_finite",
Expand All @@ -183,7 +179,7 @@ impl<'c> Translation<'c> {
self.import_num_traits(args[0])?;

// isinf_sign(x) -> fabs(x) == infinity ? (signbit(x) ? -1 : 1) : 0
let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|x| {
let inner_cond = mk().method_call_expr(x.clone(), "is_sign_positive", vec![]);
let one = mk().lit_expr(mk().int_lit(1, ""));
Expand All @@ -202,10 +198,10 @@ impl<'c> Translation<'c> {
// https://github.com/llvm-mirror/llvm/blob/master/lib/CodeGen/IntrinsicLowering.cpp#L470
Ok(WithStmts::new_val(mk().lit_expr(mk().int_lit(1, "i32"))))
}
"__builtin_expect" => self.convert_expr(ctx.used(), args[0], None),
"__builtin_expect" => self.convert_expr(ctx, args[0], None),

"__builtin_popcount" | "__builtin_popcountl" | "__builtin_popcountll" => {
let val = self.convert_expr(ctx.used(), args[0], None)?;
let val = self.convert_expr(ctx, args[0], None)?;
Ok(val.map(|x| {
let zeros = mk().method_call_expr(x, "count_ones", vec![]);
mk().cast_expr(zeros, mk().path_ty(vec!["i32"]))
Expand All @@ -216,9 +212,14 @@ impl<'c> Translation<'c> {
let n_stmts = self.convert_expr(ctx.used(), args[1], None)?;
let write_bytes = mk().abs_path_expr(vec!["core", "ptr", "write_bytes"]);
let zero = mk().lit_expr(mk().int_lit(0, "u8"));
Ok(ptr_stmts.and_then(|ptr| {
let call = ptr_stmts.and_then(|ptr| {
n_stmts.map(|n| mk().call_expr(write_bytes, vec![ptr, zero, n]))
}))
});
Ok(self.convert_side_effects_expr(
ctx,
call,
"__builtin_bzero value is not supposed to be used",
))
}

// If the target does not support data prefetch, the address expression is evaluated if
Expand Down Expand Up @@ -302,8 +303,8 @@ impl<'c> Translation<'c> {
// We can't convert this to Rust, but it should be safe to always return -1/0
// (depending on the value of `type`), so we emit the following:
// `(if (type & 2) == 0 { -1isize } else { 0isize }) as libc::size_t`
let ptr_arg = self.convert_expr(ctx.unused(), args[0], None)?;
let type_arg = self.convert_expr(ctx.used(), args[1], None)?;
let ptr_arg = self.convert_expr(ctx, args[0], None)?;
let type_arg = self.convert_expr(ctx, args[1], None)?;
Ok(ptr_arg.and_then(|_| {
type_arg.map(|type_arg| {
let type_and_2 = mk().binary_expr(
Expand All @@ -330,7 +331,7 @@ impl<'c> Translation<'c> {
}

"__builtin_va_start" => {
if ctx.is_unused() && args.len() == 2 {
if !ctx.is_used && args.len() == 2 {
if let Some(va_id) = self.match_vastart(args[0]) {
if self.ast_context.get_decl(&va_id).is_some() {
let dst = self.convert_expr(ctx.used(), args[0], None)?;
Expand All @@ -352,7 +353,7 @@ impl<'c> Translation<'c> {
Err(TranslationError::generic("Unsupported va_start"))
}
"__builtin_va_copy" => {
if ctx.is_unused() && args.len() == 2 {
if !ctx.is_used && args.len() == 2 {
if let Some((_dst_va_id, _src_va_id)) = self.match_vacopy(args[0], args[1]) {
let dst = self.convert_expr(ctx.used(), args[0], None)?;
let src = self.convert_expr(ctx.used(), args[1], None)?;
Expand All @@ -370,7 +371,7 @@ impl<'c> Translation<'c> {
Err(TranslationError::generic("Unsupported va_copy"))
}
"__builtin_va_end" => {
if ctx.is_unused() && args.len() == 1 {
if !ctx.is_used && args.len() == 1 {
if let Some(_va_id) = self.match_vaend(args[0]) {
// nothing to do since the translated Rust `va_list` values get `Drop`'ed.
return Ok(WithStmts::new_val(self.panic("va_end stub")));
Expand Down Expand Up @@ -602,7 +603,7 @@ impl<'c> Translation<'c> {
}
// There's currently no way to replicate this functionality in Rust, so we just
// pass the ptr input param in its place.
"__builtin_assume_aligned" => Ok(self.convert_expr(ctx.used(), args[0], None)?),
"__builtin_assume_aligned" => self.convert_expr(ctx, args[0], None),
// Skip over, there's no way to implement it in Rust
"__builtin_unwind_init" => Ok(WithStmts::new_val(self.panic_or_err("no value"))),
"__builtin_unreachable" => Ok(WithStmts::new(
Expand Down
14 changes: 7 additions & 7 deletions c2rust-transpile/src/translator/literals.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -199,8 +199,8 @@ impl<'c> Translation<'c> {
) -> TranslationResult<WithStmts<Box<Expr>>> {
// C compound literals are lvalues, but equivalent Rust expressions generally are not.
// So if an address is needed, store it in an intermediate variable first.
if !ctx.needs_address || ctx.expanding_macro.is_some() {
return self.convert_expr(ctx, val, override_ty);
if !ctx.needs_address || !ctx.is_used || ctx.expanding_macro.is_some() {
return self.convert_expr(ctx.not_needs_address(), val, override_ty);
}

let fresh_name = self
Expand All @@ -211,7 +211,7 @@ impl<'c> Translation<'c> {

// Translate the expression to be assigned to the fresh variable.
// It will be assigned by value, so we don't need its address anymore.
let val = self.convert_expr(ctx.not_needs_address(), val, override_ty)?;
let val = self.convert_expr(ctx.used().not_needs_address(), val, override_ty)?;

// If we are translating a static variable,
// then the fresh variable should also be static.
Expand Down Expand Up @@ -258,7 +258,7 @@ impl<'c> Translation<'c> {

let to_array_element = |id: CExprId| -> TranslationResult<_> {
let val =
self.convert_expr(ctx.used(), id, Some(CQualTypeId::new(element_type_id)))?;
self.convert_expr(ctx, id, Some(CQualTypeId::new(element_type_id)))?;
val.try_map(|x| {
// Array literals require all of their elements to be
// the correct type; they will not use implicit casts to
Expand Down Expand Up @@ -325,7 +325,7 @@ impl<'c> Translation<'c> {
// * `ptr_extra_braces`
// * `array_of_ptrs`
// * `array_of_arrays`
self.convert_expr(ctx.used(), single, expected_type_id)
self.convert_expr(ctx, single, expected_type_id)
}
&[single] if is_zero_literal(single) && n > 1 => {
// This was likely a C array of the form `int x[16] = { 0 }`.
Expand Down Expand Up @@ -364,9 +364,9 @@ impl<'c> Translation<'c> {
}
ref kind if kind.is_scalar() => {
if let Some(&first) = ids.first() {
self.convert_expr(ctx.used(), first, expected_type_id)
self.convert_expr(ctx, first, expected_type_id)
} else {
self.implicit_default_expr(ctx.used(), result_type_id.ctype)
self.implicit_default_expr(ctx, result_type_id.ctype)
}
}
ref t => Err(format_err!("Init list not implemented for {:?}", t).into()),
Expand Down
2 changes: 1 addition & 1 deletion c2rust-transpile/src/translator/macros.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,7 @@ impl<'c> Translation<'c> {
.kind
.get_type()
.ok_or_else(|| format_err!("Invalid expression type"))?;
let expr = self.convert_expr(ctx, id, None)?;
let expr = self.convert_expr(ctx.used(), id, None)?;

// Join ty and cur_ty to the smaller of the two types. If the
// types are not cast-compatible, abort the fold.
Expand Down
Loading
Loading