bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

const-eval: detect more pointers as definitely not-null

Browse source
This commit is contained in:
Ralf Jung 2024-12-01 12:59:50 +01:00
parent d61f55d8b9
commit e1dda10057
3 changed files with 25 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

25
compiler/rustc_const_eval/src/interpret/memory.rs
View file

@ -1481,22 +1481,31 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
/// Test if this value might be null.
/// If the machine does not support ptr-to-int casts, this is conservative.
pub fn scalar_may_be_null(&self, scalar: Scalar<M::Provenance>) -> InterpResult<'tcx, bool> {
interp_ok(match scalar.try_to_scalar_int() {
Ok(int) => int.is_null(),
match scalar.try_to_scalar_int() {
Ok(int) => interp_ok(int.is_null()),
Err(_) => {
// Can only happen during CTFE.
// We can't cast this pointer to an integer. Can only happen during CTFE.
let ptr = scalar.to_pointer(self)?;
match self.ptr_try_get_alloc_id(ptr, 0) {
Ok((alloc_id, offset, _)) => {
let size = self.get_alloc_info(alloc_id).size;
// If the pointer is out-of-bounds, it may be null.
// Note that one-past-the-end (offset == size) is still inbounds, and never null.
offset > size
let info = self.get_alloc_info(alloc_id);
// If the pointer is in-bounds (including "at the end"), it is definitely not null.
if offset <= info.size {
return interp_ok(false);
}
// If the allocation is N-aligned, and the offset is not divisible by N,
// then `base + offset` has a non-zero remainder after division by `N`,
// which means `base + offset` cannot be null.
if offset.bytes() % info.align.bytes() != 0 {
return interp_ok(false);
}
// We don't know enough, this might be null.
interp_ok(true)
}
Err(_offset) => bug!("a non-int scalar is always a pointer"),
}
}
})
}
}
/// Turning a "maybe pointer" into a proper pointer (and some information