mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Auto merge of #109792 - cjgillot:reachable-lint, r=oli-obk

Browse Source 
Only visit reachable blocks in ConstProp lint.

Fixes https://github.com/rust-lang/rust/issues/78803
Fixes https://github.com/rust-lang/rust/issues/109731
This commit is contained in:
bors 2023-04-06 03:05:47 +00:00
commit f211da7101
3 changed files with 155 additions and 132 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

271
compiler/rustc_mir_transform/src/const_prop_lint.rs
View File

@ -1,7 +1,7 @@
//! Propagates constants for early reporting of statically known
//! assertion failures
use either::{Left, Right};
use either::Left;
use rustc_const_eval::interpret::Immediate;
use rustc_const_eval::interpret::{
@ -9,7 +9,7 @@ use rustc_const_eval::interpret::{
};
use rustc_hir::def::DefKind;
use rustc_hir::HirId;
use rustc_index::vec::IndexSlice;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
@ -130,11 +130,8 @@ struct ConstPropagator<'mir, 'tcx> {
ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
source_scopes: &'mir IndexSlice<SourceScope, SourceScopeData<'tcx>>,
local_decls: &'mir IndexSlice<Local, LocalDecl<'tcx>>,
// Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
// the last known `SourceInfo` here and just keep revisiting it.
source_info: Option<SourceInfo>,
worklist: Vec<BasicBlock>,
visited_blocks: BitSet<BasicBlock>,
}
impl<'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'_, 'tcx> {
@ -213,12 +210,19 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
ecx,
tcx,
param_env,
source_scopes: &dummy_body.source_scopes,
local_decls: &dummy_body.local_decls,
source_info: None,
worklist: vec![START_BLOCK],
visited_blocks: BitSet::new_empty(body.basic_blocks.len()),
}
}
fn body(&self) -> &'mir Body<'tcx> {
self.ecx.frame().body
}
fn local_decls(&self) -> &'mir LocalDecls<'tcx> {
&self.body().local_decls
}
fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
let op = match self.ecx.eval_place_to_op(place, None) {
Ok(op) => {
@ -251,15 +255,15 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
}
fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
source_info.scope.lint_root(self.source_scopes)
source_info.scope.lint_root(&self.body().source_scopes)
}
fn use_ecx<F, T>(&mut self, source_info: SourceInfo, f: F) -> Option<T>
fn use_ecx<F, T>(&mut self, location: Location, f: F) -> Option<T>
where
F: FnOnce(&mut Self) -> InterpResult<'tcx, T>,
{
// Overwrite the PC -- whatever the interpreter does to it does not make any sense anyway.
self.ecx.frame_mut().loc = Right(source_info.span);
self.ecx.frame_mut().loc = Left(location);
match f(self) {
Ok(val) => Some(val),
Err(error) => {
@ -278,7 +282,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
}
/// Returns the value, if any, of evaluating `c`.
fn eval_constant(&mut self, c: &Constant<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
fn eval_constant(&mut self, c: &Constant<'tcx>, location: Location) -> Option<OpTy<'tcx>> {
// FIXME we need to revisit this for #67176
if c.needs_subst() {
return None;
@ -292,45 +296,41 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
// manually normalized.
let val = self.tcx.try_normalize_erasing_regions(self.param_env, c.literal).ok()?;
self.use_ecx(source_info, |this| this.ecx.eval_mir_constant(&val, Some(c.span), None))
self.use_ecx(location, |this| this.ecx.eval_mir_constant(&val, Some(c.span), None))
}
/// Returns the value, if any, of evaluating `place`.
fn eval_place(&mut self, place: Place<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
fn eval_place(&mut self, place: Place<'tcx>, location: Location) -> Option<OpTy<'tcx>> {
trace!("eval_place(place={:?})", place);
self.use_ecx(source_info, |this| this.ecx.eval_place_to_op(place, None))
self.use_ecx(location, |this| this.ecx.eval_place_to_op(place, None))
}
/// Returns the value, if any, of evaluating `op`. Calls upon `eval_constant`
/// or `eval_place`, depending on the variant of `Operand` used.
fn eval_operand(&mut self, op: &Operand<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
fn eval_operand(&mut self, op: &Operand<'tcx>, location: Location) -> Option<OpTy<'tcx>> {
match *op {
Operand::Constant(ref c) => self.eval_constant(c, source_info),
Operand::Move(place) | Operand::Copy(place) => self.eval_place(place, source_info),
Operand::Constant(ref c) => self.eval_constant(c, location),
Operand::Move(place) | Operand::Copy(place) => self.eval_place(place, location),
}
}
fn report_assert_as_lint(
&self,
lint: &'static lint::Lint,
source_info: SourceInfo,
location: Location,
message: &'static str,
panic: AssertKind<impl std::fmt::Debug>,
) {
if let Some(lint_root) = self.lint_root(source_info) {
let source_info = self.body().source_info(location);
if let Some(lint_root) = self.lint_root(*source_info) {
self.tcx.struct_span_lint_hir(lint, lint_root, source_info.span, message, |lint| {
lint.span_label(source_info.span, format!("{:?}", panic))
});
}
}
fn check_unary_op(
&mut self,
op: UnOp,
arg: &Operand<'tcx>,
source_info: SourceInfo,
) -> Option<()> {
if let (val, true) = self.use_ecx(source_info, |this| {
fn check_unary_op(&mut self, op: UnOp, arg: &Operand<'tcx>, location: Location) -> Option<()> {
if let (val, true) = self.use_ecx(location, |this| {
let val = this.ecx.read_immediate(&this.ecx.eval_operand(arg, None)?)?;
let (_res, overflow, _ty) = this.ecx.overflowing_unary_op(op, &val)?;
Ok((val, overflow))
@ -340,7 +340,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
assert_eq!(op, UnOp::Neg, "Neg is the only UnOp that can overflow");
self.report_assert_as_lint(
lint::builtin::ARITHMETIC_OVERFLOW,
source_info,
location,
"this arithmetic operation will overflow",
AssertKind::OverflowNeg(val.to_const_int()),
);
@ -355,28 +355,27 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
op: BinOp,
left: &Operand<'tcx>,
right: &Operand<'tcx>,
source_info: SourceInfo,
location: Location,
) -> Option<()> {
let r = self.use_ecx(source_info, |this| {
let r = self.use_ecx(location, |this| {
this.ecx.read_immediate(&this.ecx.eval_operand(right, None)?)
});
let l = self.use_ecx(source_info, |this| {
this.ecx.read_immediate(&this.ecx.eval_operand(left, None)?)
});
let l = self
.use_ecx(location, |this| this.ecx.read_immediate(&this.ecx.eval_operand(left, None)?));
// Check for exceeding shifts *even if* we cannot evaluate the LHS.
if matches!(op, BinOp::Shr | BinOp::Shl) {
let r = r.clone()?;
// We need the type of the LHS. We cannot use `place_layout` as that is the type
// of the result, which for checked binops is not the same!
let left_ty = left.ty(self.local_decls, self.tcx);
let left_ty = left.ty(self.local_decls(), self.tcx);
let left_size = self.ecx.layout_of(left_ty).ok()?.size;
let right_size = r.layout.size;
let r_bits = r.to_scalar().to_bits(right_size).ok();
if r_bits.map_or(false, |b| b >= left_size.bits() as u128) {
debug!("check_binary_op: reporting assert for {:?}", source_info);
debug!("check_binary_op: reporting assert for {:?}", location);
self.report_assert_as_lint(
lint::builtin::ARITHMETIC_OVERFLOW,
source_info,
location,
"this arithmetic operation will overflow",
AssertKind::Overflow(
op,
@ -398,13 +397,13 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
if let (Some(l), Some(r)) = (l, r) {
// The remaining operators are handled through `overflowing_binary_op`.
if self.use_ecx(source_info, |this| {
if self.use_ecx(location, |this| {
let (_res, overflow, _ty) = this.ecx.overflowing_binary_op(op, &l, &r)?;
Ok(overflow)
})? {
self.report_assert_as_lint(
lint::builtin::ARITHMETIC_OVERFLOW,
source_info,
location,
"this arithmetic operation will overflow",
AssertKind::Overflow(op, l.to_const_int(), r.to_const_int()),
);
@ -414,7 +413,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
Some(())
}
fn check_rvalue(&mut self, rvalue: &Rvalue<'tcx>, source_info: SourceInfo) -> Option<()> {
fn check_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) -> Option<()> {
// Perform any special handling for specific Rvalue types.
// Generally, checks here fall into one of two categories:
// 1. Additional checking to provide useful lints to the user
@ -429,11 +428,11 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
// lint.
Rvalue::UnaryOp(op, arg) => {
trace!("checking UnaryOp(op = {:?}, arg = {:?})", op, arg);
self.check_unary_op(*op, arg, source_info)?;
self.check_unary_op(*op, arg, location)?;
}
Rvalue::BinaryOp(op, box (left, right)) => {
trace!("checking BinaryOp(op = {:?}, left = {:?}, right = {:?})", op, left, right);
self.check_binary_op(*op, left, right, source_info)?;
self.check_binary_op(*op, left, right, location)?;
}
Rvalue::CheckedBinaryOp(op, box (left, right)) => {
trace!(
@ -442,7 +441,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
left,
right
);
self.check_binary_op(*op, left, right, source_info)?;
self.check_binary_op(*op, left, right, location)?;
}
// Do not try creating references (#67862)
@ -481,10 +480,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
if rvalue.needs_subst() {
return None;
}
if !rvalue
.ty(&self.ecx.frame().body.local_decls, *self.ecx.tcx)
.is_sized(*self.ecx.tcx, self.param_env)
{
if !rvalue.ty(self.local_decls(), self.tcx).is_sized(self.tcx, self.param_env) {
// the interpreter doesn't support unsized locals (only unsized arguments),
// but rustc does (in a kinda broken way), so we have to skip them here
return None;
@ -493,12 +489,80 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
Some(())
}
fn check_assertion(
&mut self,
expected: bool,
msg: &AssertKind<Operand<'tcx>>,
cond: &Operand<'tcx>,
location: Location,
) -> Option<!> {
let ref value = self.eval_operand(&cond, location)?;
trace!("assertion on {:?} should be {:?}", value, expected);
let expected = Scalar::from_bool(expected);
let value_const = self.use_ecx(location, |this| this.ecx.read_scalar(&value))?;
if expected != value_const {
// Poison all places this operand references so that further code
// doesn't use the invalid value
if let Some(place) = cond.place() {
Self::remove_const(&mut self.ecx, place.local);
}
enum DbgVal<T> {
Val(T),
Underscore,
}
impl<T: std::fmt::Debug> std::fmt::Debug for DbgVal<T> {
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Val(val) => val.fmt(fmt),
Self::Underscore => fmt.write_str("_"),
}
}
}
let mut eval_to_int = |op| {
// This can be `None` if the lhs wasn't const propagated and we just
// triggered the assert on the value of the rhs.
self.eval_operand(op, location)
.and_then(|op| self.ecx.read_immediate(&op).ok())
.map_or(DbgVal::Underscore, |op| DbgVal::Val(op.to_const_int()))
};
let msg = match msg {
AssertKind::DivisionByZero(op) => AssertKind::DivisionByZero(eval_to_int(op)),
AssertKind::RemainderByZero(op) => AssertKind::RemainderByZero(eval_to_int(op)),
AssertKind::Overflow(bin_op @ (BinOp::Div | BinOp::Rem), op1, op2) => {
// Division overflow is *UB* in the MIR, and different than the
// other overflow checks.
AssertKind::Overflow(*bin_op, eval_to_int(op1), eval_to_int(op2))
}
AssertKind::BoundsCheck { ref len, ref index } => {
let len = eval_to_int(len);
let index = eval_to_int(index);
AssertKind::BoundsCheck { len, index }
}
// Remaining overflow errors are already covered by checks on the binary operators.
AssertKind::Overflow(..) | AssertKind::OverflowNeg(_) => return None,
// Need proper const propagator for these.
_ => return None,
};
self.report_assert_as_lint(
lint::builtin::UNCONDITIONAL_PANIC,
location,
"this operation will panic at runtime",
msg,
);
}
None
}
fn ensure_not_propagated(&self, local: Local) {
if cfg!(debug_assertions) {
assert!(
self.get_const(local.into()).is_none()
|| self
.layout_of(self.local_decls[local].ty)
.layout_of(self.local_decls()[local].ty)
.map_or(true, |layout| layout.is_zst()),
"failed to remove values for `{local:?}`, value={:?}",
self.get_const(local.into()),
@ -509,7 +573,12 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
fn visit_body(&mut self, body: &Body<'tcx>) {
for (bb, data) in body.basic_blocks.iter_enumerated() {
while let Some(bb) = self.worklist.pop() {
if !self.visited_blocks.insert(bb) {
continue;
}
let data = &body.basic_blocks[bb];
self.visit_basic_block_data(bb, data);
}
}
@ -521,14 +590,13 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
trace!("visit_constant: {:?}", constant);
self.super_constant(constant, location);
self.eval_constant(constant, self.source_info.unwrap());
self.eval_constant(constant, location);
}
fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
self.super_assign(place, rvalue, location);
let source_info = self.source_info.unwrap();
let Some(()) = self.check_rvalue(rvalue, source_info) else { return };
let Some(()) = self.check_rvalue(rvalue, location) else { return };
match self.ecx.machine.can_const_prop[place.local] {
// Do nothing if the place is indirect.
@ -536,7 +604,7 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
ConstPropMode::NoPropagation => self.ensure_not_propagated(place.local),
ConstPropMode::OnlyInsideOwnBlock | ConstPropMode::FullConstProp => {
if self
.use_ecx(source_info, |this| this.ecx.eval_rvalue_into_place(rvalue, *place))
.use_ecx(location, |this| this.ecx.eval_rvalue_into_place(rvalue, *place))
.is_none()
{
// Const prop failed, so erase the destination, ensuring that whatever happens
@ -562,8 +630,6 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
trace!("visit_statement: {:?}", statement);
let source_info = statement.source_info;
self.source_info = Some(source_info);
// We want to evaluate operands before any change to the assigned-to value,
// so we recurse first.
@ -576,8 +642,7 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
_ if place.is_indirect() => {}
ConstPropMode::NoPropagation => self.ensure_not_propagated(place.local),
ConstPropMode::FullConstProp | ConstPropMode::OnlyInsideOwnBlock => {
if self.use_ecx(source_info, |this| this.ecx.statement(statement)).is_some()
{
if self.use_ecx(location, |this| this.ecx.statement(statement)).is_some() {
trace!("propped discriminant into {:?}", place);
} else {
Self::remove_const(&mut self.ecx, place.local);
@ -599,83 +664,24 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
}
fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
let source_info = terminator.source_info;
self.source_info = Some(source_info);
self.super_terminator(terminator, location);
match &terminator.kind {
TerminatorKind::Assert { expected, ref msg, ref cond, .. } => {
if let Some(ref value) = self.eval_operand(&cond, source_info) {
trace!("assertion on {:?} should be {:?}", value, expected);
let expected = Scalar::from_bool(*expected);
let Ok(value_const) = self.ecx.read_scalar(&value) else {
// FIXME should be used use_ecx rather than a local match... but we have
// quite a few of these read_scalar/read_immediate that need fixing.
return
};
if expected != value_const {
enum DbgVal<T> {
Val(T),
Underscore,
}
impl<T: std::fmt::Debug> std::fmt::Debug for DbgVal<T> {
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Val(val) => val.fmt(fmt),
Self::Underscore => fmt.write_str("_"),
}
}
}
let mut eval_to_int = |op| {
// This can be `None` if the lhs wasn't const propagated and we just
// triggered the assert on the value of the rhs.
self.eval_operand(op, source_info)
.and_then(|op| self.ecx.read_immediate(&op).ok())
.map_or(DbgVal::Underscore, |op| DbgVal::Val(op.to_const_int()))
};
let msg = match msg {
AssertKind::DivisionByZero(op) => {
Some(AssertKind::DivisionByZero(eval_to_int(op)))
}
AssertKind::RemainderByZero(op) => {
Some(AssertKind::RemainderByZero(eval_to_int(op)))
}
AssertKind::Overflow(bin_op @ (BinOp::Div | BinOp::Rem), op1, op2) => {
// Division overflow is *UB* in the MIR, and different than the
// other overflow checks.
Some(AssertKind::Overflow(
*bin_op,
eval_to_int(op1),
eval_to_int(op2),
))
}
AssertKind::BoundsCheck { ref len, ref index } => {
let len = eval_to_int(len);
let index = eval_to_int(index);
Some(AssertKind::BoundsCheck { len, index })
}
// Remaining overflow errors are already covered by checks on the binary operators.
AssertKind::Overflow(..) | AssertKind::OverflowNeg(_) => None,
// Need proper const propagator for these.
_ => None,
};
// Poison all places this operand references so that further code
// doesn't use the invalid value
match cond {
Operand::Move(ref place) | Operand::Copy(ref place) => {
Self::remove_const(&mut self.ecx, place.local);
}
Operand::Constant(_) => {}
}
if let Some(msg) = msg {
self.report_assert_as_lint(
lint::builtin::UNCONDITIONAL_PANIC,
source_info,
"this operation will panic at runtime",
msg,
);
}
}
self.check_assertion(*expected, msg, cond, location);
}
TerminatorKind::SwitchInt { ref discr, ref targets } => {
if let Some(ref value) = self.eval_operand(&discr, location)
&& let Some(value_const) = self.use_ecx(location, |this| this.ecx.read_scalar(&value))
&& let Ok(constant) = value_const.try_to_int()
&& let Ok(constant) = constant.to_bits(constant.size())
{
// We managed to evaluate the discriminant, so we know we only need to visit
// one target.
let target = targets.target_for_value(constant);
self.worklist.push(target);
return;
}
// We failed to evaluate the discriminant, fallback to visiting all successors.
}
// None of these have Operands to const-propagate.
TerminatorKind::Goto { .. }
@ -688,10 +694,11 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
| TerminatorKind::GeneratorDrop
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::SwitchInt { .. }
| TerminatorKind::Call { .. }
| TerminatorKind::InlineAsm { .. } => {}
}
self.worklist.extend(terminator.successors());
}
fn visit_basic_block_data(&mut self, block: BasicBlock, data: &BasicBlockData<'tcx>) {

6
tests/ui/const_prop/unreachable-bounds.rs Normal file
View File

@ -0,0 +1,6 @@
// Use `build-pass` to ensure const-prop lint runs.
// build-pass
fn main() {
[()][if false { 1 } else { return }]
}

10
tests/ui/const_prop/unreachable-overflow.rs Normal file
View File

@ -0,0 +1,10 @@
// Use `build-pass` to ensure const-prop lint runs.
// build-pass
fn main() {
let x = 2u32;
let y = 3u32;
if y <= x {
dbg!(x - y);
}
}