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make redundant StorageLive UB

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This commit is contained in:
Ralf Jung 2020-11-21 20:23:00 +01:00
parent cc03ee6702
commit 78deacc2ec
2 changed files with 16 additions and 23 deletions
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33
compiler/rustc_mir/src/interpret/eval_context.rs
View File

@ -840,36 +840,31 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
Ok(())
}
/// Mark a storage as live, killing the previous content and returning it.
/// Remember to deallocate that!
pub fn storage_live(
&mut self,
local: mir::Local,
) -> InterpResult<'tcx, LocalValue<M::PointerTag>> {
/// Mark a storage as live, killing the previous content.
pub fn storage_live(&mut self, local: mir::Local) -> InterpResult<'tcx> {
assert!(local != mir::RETURN_PLACE, "Cannot make return place live");
trace!("{:?} is now live", local);
let local_val = LocalValue::Uninitialized;
// StorageLive *always* kills the value that's currently stored.
// However, we do not error if the variable already is live;
// see <https://github.com/rust-lang/rust/issues/42371>.
Ok(mem::replace(&mut self.frame_mut().locals[local].value, local_val))
// StorageLive expects the local to be dead, and marks it live.
let old = mem::replace(&mut self.frame_mut().locals[local].value, local_val);
if !matches!(old, LocalValue::Dead) {
throw_ub_format!("StorageLive on a local that was already live");
}
Ok(())
}
/// Returns the old value of the local.
/// Remember to deallocate that!
pub fn storage_dead(&mut self, local: mir::Local) -> LocalValue<M::PointerTag> {
pub fn storage_dead(&mut self, local: mir::Local) -> InterpResult<'tcx> {
assert!(local != mir::RETURN_PLACE, "Cannot make return place dead");
trace!("{:?} is now dead", local);
mem::replace(&mut self.frame_mut().locals[local].value, LocalValue::Dead)
// It is entirely okay for this local to be already dead (at least that's how we currently generate MIR)
let old = mem::replace(&mut self.frame_mut().locals[local].value, LocalValue::Dead);
self.deallocate_local(old)?;
Ok(())
}
pub(super) fn deallocate_local(
&mut self,
local: LocalValue<M::PointerTag>,
) -> InterpResult<'tcx> {
// FIXME: should we tell the user that there was a local which was never written to?
fn deallocate_local(&mut self, local: LocalValue<M::PointerTag>) -> InterpResult<'tcx> {
if let LocalValue::Live(Operand::Indirect(MemPlace { ptr, .. })) = local {
// All locals have a backing allocation, even if the allocation is empty
// due to the local having ZST type.

6
compiler/rustc_mir/src/interpret/step.rs
View File

@ -95,14 +95,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// Mark locals as alive
StorageLive(local) => {
let old_val = self.storage_live(*local)?;
self.deallocate_local(old_val)?;
self.storage_live(*local)?;
}
// Mark locals as dead
StorageDead(local) => {
let old_val = self.storage_dead(*local);
self.deallocate_local(old_val)?;
self.storage_dead(*local)?;
}
// No dynamic semantics attached to `FakeRead`; MIR