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adjust constValue::Slice to work for arbitrary slice types

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This commit is contained in:
Ralf Jung 2023-09-15 15:59:47 +02:00
parent 0692db1a90
commit ea22adbabd
12 changed files with 75 additions and 63 deletions
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25
compiler/rustc_const_eval/src/const_eval/eval_queries.rs
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@ -151,19 +151,26 @@ pub(super) fn op_to_const<'tcx>(
Immediate::Scalar(x) => ConstValue::Scalar(x),
Immediate::ScalarPair(a, b) => {
debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
// FIXME: assert that this has an appropriate type.
// Currently we actually get here for non-[u8] slices during valtree construction!
let msg = "`op_to_const` on an immediate scalar pair must only be used on slice references to actually allocated memory";
// This codepath solely exists for `valtree_to_const_value` to not need to generate
// a `ConstValue::Indirect` for wide references, so it is tightly restricted to just
// that case.
let pointee_ty = imm.layout.ty.builtin_deref(false).unwrap().ty; // `false` = no raw ptrs
debug_assert!(
matches!(
ecx.tcx.struct_tail_without_normalization(pointee_ty).kind(),
ty::Str | ty::Slice(..),
),
"`ConstValue::Slice` is for slice-tailed types only, but got {}",
imm.layout.ty,
);
let msg = "`op_to_const` on an immediate scalar pair must only be used on slice references to the beginning of an actual allocation";
// We know `offset` is relative to the allocation, so we can use `into_parts`.
// We use `ConstValue::Slice` so that we don't have to generate an allocation for
// `ConstValue::Indirect` here.
let (alloc_id, offset) = a.to_pointer(ecx).expect(msg).into_parts();
let alloc_id = alloc_id.expect(msg);
let data = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
let start = offset.bytes_usize();
let len = b.to_target_usize(ecx).expect(msg);
let len: usize = len.try_into().unwrap();
ConstValue::Slice { data, start, end: start + len }
assert!(offset == abi::Size::ZERO, "{}", msg);
let meta = b.to_target_usize(ecx).expect(msg);
ConstValue::Slice { data, meta }
}
Immediate::Uninit => bug!("`Uninit` is not a valid value for {}", op.layout.ty),
},