1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
use super::eval_queries::{mk_eval_cx, op_to_const};
use super::machine::CompileTimeEvalContext;
use super::{ValTreeCreationError, ValTreeCreationResult, VALTREE_MAX_NODES};
use crate::interpret::{
    intern_const_alloc_recursive, ConstValue, ImmTy, Immediate, InternKind, MemPlaceMeta,
    MemoryKind, PlaceTy, Scalar, ScalarMaybeUninit,
};
use crate::interpret::{MPlaceTy, Value};
use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
use rustc_span::source_map::DUMMY_SP;
use rustc_target::abi::{Align, VariantIdx};

#[instrument(skip(ecx), level = "debug")]
fn branches<'tcx>(
    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
    place: &MPlaceTy<'tcx>,
    n: usize,
    variant: Option<VariantIdx>,
    num_nodes: &mut usize,
) -> ValTreeCreationResult<'tcx> {
    let place = match variant {
        Some(variant) => ecx.mplace_downcast(&place, variant).unwrap(),
        None => *place,
    };
    let variant = variant.map(|variant| Some(ty::ValTree::Leaf(ScalarInt::from(variant.as_u32()))));
    debug!(?place, ?variant);

    let mut fields = Vec::with_capacity(n);
    for i in 0..n {
        let field = ecx.mplace_field(&place, i).unwrap();
        let valtree = const_to_valtree_inner(ecx, &field, num_nodes)?;
        fields.push(Some(valtree));
    }

    // For enums, we prepend their variant index before the variant's fields so we can figure out
    // the variant again when just seeing a valtree.
    let branches = variant
        .into_iter()
        .chain(fields.into_iter())
        .collect::<Option<Vec<_>>>()
        .expect("should have already checked for errors in ValTree creation");

    // Have to account for ZSTs here
    if branches.len() == 0 {
        *num_nodes += 1;
    }

    Ok(ty::ValTree::Branch(ecx.tcx.arena.alloc_from_iter(branches)))
}

#[instrument(skip(ecx), level = "debug")]
fn slice_branches<'tcx>(
    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
    place: &MPlaceTy<'tcx>,
    num_nodes: &mut usize,
) -> ValTreeCreationResult<'tcx> {
    let n = place
        .len(&ecx.tcx.tcx)
        .unwrap_or_else(|_| panic!("expected to use len of place {:?}", place));

    let mut elems = Vec::with_capacity(n as usize);
    for i in 0..n {
        let place_elem = ecx.mplace_index(place, i).unwrap();
        let valtree = const_to_valtree_inner(ecx, &place_elem, num_nodes)?;
        elems.push(valtree);
    }

    Ok(ty::ValTree::Branch(ecx.tcx.arena.alloc_from_iter(elems)))
}

#[instrument(skip(ecx), level = "debug")]
pub(crate) fn const_to_valtree_inner<'tcx>(
    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
    place: &MPlaceTy<'tcx>,
    num_nodes: &mut usize,
) -> ValTreeCreationResult<'tcx> {
    let ty = place.layout.ty;
    debug!("ty kind: {:?}", ty.kind());

    if *num_nodes >= VALTREE_MAX_NODES {
        return Err(ValTreeCreationError::NodesOverflow);
    }

    match ty.kind() {
        ty::FnDef(..) => {
            *num_nodes += 1;
            Ok(ty::ValTree::zst())
        }
        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => {
            let Ok(val) = ecx.read_immediate(&place.into()) else {
                return Err(ValTreeCreationError::Other);
            };
            let val = val.to_scalar().unwrap();
            *num_nodes += 1;

            Ok(ty::ValTree::Leaf(val.assert_int()))
        }

        // Raw pointers are not allowed in type level constants, as we cannot properly test them for
        // equality at compile-time (see `ptr_guaranteed_eq`/`_ne`).
        // Technically we could allow function pointers (represented as `ty::Instance`), but this is not guaranteed to
        // agree with runtime equality tests.
        ty::FnPtr(_) | ty::RawPtr(_) => Err(ValTreeCreationError::NonSupportedType),

        ty::Ref(_, _, _)  => {
            let Ok(derefd_place)= ecx.deref_operand(&place.into()) else {
                return Err(ValTreeCreationError::Other);
            };
            debug!(?derefd_place);

            const_to_valtree_inner(ecx, &derefd_place, num_nodes)
        }

        ty::Str | ty::Slice(_) | ty::Array(_, _) => {
            slice_branches(ecx, place, num_nodes)
        }
        // Trait objects are not allowed in type level constants, as we have no concept for
        // resolving their backing type, even if we can do that at const eval time. We may
        // hypothetically be able to allow `dyn StructuralEq` trait objects in the future,
        // but it is unclear if this is useful.
        ty::Dynamic(..) => Err(ValTreeCreationError::NonSupportedType),

        ty::Tuple(elem_tys) => {
            branches(ecx, place, elem_tys.len(), None, num_nodes)
        }

        ty::Adt(def, _) => {
            if def.is_union() {
                return Err(ValTreeCreationError::NonSupportedType);
            } else if def.variants().is_empty() {
                bug!("uninhabited types should have errored and never gotten converted to valtree")
            }

            let Ok((_, variant)) = ecx.read_discriminant(&place.into()) else {
                return Err(ValTreeCreationError::Other);
            };
            branches(ecx, place, def.variant(variant).fields.len(), def.is_enum().then_some(variant), num_nodes)
        }

        ty::Never
        | ty::Error(_)
        | ty::Foreign(..)
        | ty::Infer(ty::FreshIntTy(_))
        | ty::Infer(ty::FreshFloatTy(_))
        | ty::Projection(..)
        | ty::Param(_)
        | ty::Bound(..)
        | ty::Placeholder(..)
        // FIXME(oli-obk): we could look behind opaque types
        | ty::Opaque(..)
        | ty::Infer(_)
        // FIXME(oli-obk): we can probably encode closures just like structs
        | ty::Closure(..)
        | ty::Generator(..)
        | ty::GeneratorWitness(..) => Err(ValTreeCreationError::NonSupportedType),
    }
}

#[instrument(skip(ecx), level = "debug")]
fn create_mplace_from_layout<'tcx>(
    ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
    ty: Ty<'tcx>,
) -> MPlaceTy<'tcx> {
    let tcx = ecx.tcx;
    let param_env = ecx.param_env;
    let layout = tcx.layout_of(param_env.and(ty)).unwrap();
    debug!(?layout);

    ecx.allocate(layout, MemoryKind::Stack).unwrap()
}

// Walks custom DSTs and gets the type of the unsized field and the number of elements
// in the unsized field.
fn get_info_on_unsized_field<'tcx>(
    ty: Ty<'tcx>,
    valtree: ty::ValTree<'tcx>,
    tcx: TyCtxt<'tcx>,
) -> (Ty<'tcx>, usize) {
    let mut last_valtree = valtree;
    let tail = tcx.struct_tail_with_normalize(
        ty,
        |ty| ty,
        || {
            let branches = last_valtree.unwrap_branch();
            last_valtree = branches[branches.len() - 1];
            debug!(?branches, ?last_valtree);
        },
    );
    let unsized_inner_ty = match tail.kind() {
        ty::Slice(t) => *t,
        ty::Str => tail,
        _ => bug!("expected Slice or Str"),
    };

    // Have to adjust type for ty::Str
    let unsized_inner_ty = match unsized_inner_ty.kind() {
        ty::Str => tcx.mk_ty(ty::Uint(ty::UintTy::U8)),
        _ => unsized_inner_ty,
    };

    // Get the number of elements in the unsized field
    let num_elems = last_valtree.unwrap_branch().len();

    (unsized_inner_ty, num_elems)
}

#[instrument(skip(ecx), level = "debug")]
fn create_pointee_place<'tcx>(
    ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
    ty: Ty<'tcx>,
    valtree: ty::ValTree<'tcx>,
) -> MPlaceTy<'tcx> {
    let tcx = ecx.tcx.tcx;

    if !ty.is_sized(ecx.tcx, ty::ParamEnv::empty()) {
        // We need to create `Allocation`s for custom DSTs

        let (unsized_inner_ty, num_elems) = get_info_on_unsized_field(ty, valtree, tcx);
        let unsized_inner_ty = match unsized_inner_ty.kind() {
            ty::Str => tcx.mk_ty(ty::Uint(ty::UintTy::U8)),
            _ => unsized_inner_ty,
        };
        let unsized_inner_ty_size =
            tcx.layout_of(ty::ParamEnv::empty().and(unsized_inner_ty)).unwrap().layout.size();
        debug!(?unsized_inner_ty, ?unsized_inner_ty_size, ?num_elems);

        // for custom DSTs only the last field/element is unsized, but we need to also allocate
        // space for the other fields/elements
        let layout = tcx.layout_of(ty::ParamEnv::empty().and(ty)).unwrap();
        let size_of_sized_part = layout.layout.size();

        // Get the size of the memory behind the DST
        let dst_size = unsized_inner_ty_size.checked_mul(num_elems as u64, &tcx).unwrap();

        let size = size_of_sized_part.checked_add(dst_size, &tcx).unwrap();
        let align = Align::from_bytes(size.bytes().next_power_of_two()).unwrap();
        let ptr = ecx.allocate_ptr(size, align, MemoryKind::Stack).unwrap();
        debug!(?ptr);

        let place = MPlaceTy::from_aligned_ptr_with_meta(
            ptr.into(),
            layout,
            MemPlaceMeta::Meta(Scalar::from_machine_usize(num_elems as u64, &tcx)),
        );
        debug!(?place);

        place
    } else {
        create_mplace_from_layout(ecx, ty)
    }
}

/// Converts a `ValTree` to a `ConstValue`, which is needed after mir
/// construction has finished.
// FIXME Merge `valtree_to_const_value` and `valtree_into_mplace` into one function
#[instrument(skip(tcx), level = "debug")]
pub fn valtree_to_const_value<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env_ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
    valtree: ty::ValTree<'tcx>,
) -> ConstValue<'tcx> {
    // Basic idea: We directly construct `Scalar` values from trivial `ValTree`s
    // (those for constants with type bool, int, uint, float or char).
    // For all other types we create an `MPlace` and fill that by walking
    // the `ValTree` and using `place_projection` and `place_field` to
    // create inner `MPlace`s which are filled recursively.
    // FIXME Does this need an example?

    let (param_env, ty) = param_env_ty.into_parts();
    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);

    match ty.kind() {
        ty::FnDef(..) => {
            assert!(valtree.unwrap_branch().is_empty());
            ConstValue::ZeroSized
        }
        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => match valtree {
            ty::ValTree::Leaf(scalar_int) => ConstValue::Scalar(Scalar::Int(scalar_int)),
            ty::ValTree::Branch(_) => bug!(
                "ValTrees for Bool, Int, Uint, Float or Char should have the form ValTree::Leaf"
            ),
        },
        ty::Ref(_, _, _) | ty::Tuple(_) | ty::Array(_, _) | ty::Adt(..) => {
            let mut place = match ty.kind() {
                ty::Ref(_, inner_ty, _) => {
                    // Need to create a place for the pointee to fill for Refs
                    create_pointee_place(&mut ecx, *inner_ty, valtree)
                }
                _ => create_mplace_from_layout(&mut ecx, ty),
            };
            debug!(?place);

            valtree_into_mplace(&mut ecx, &mut place, valtree);
            dump_place(&ecx, place.into());
            intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &place).unwrap();

            let const_val = match ty.kind() {
                ty::Ref(_, _, _) => {
                    let ref_place = place.to_ref(&tcx);
                    let imm =
                        ImmTy::from_immediate(ref_place, tcx.layout_of(param_env_ty).unwrap());

                    op_to_const(&ecx, &imm.into())
                }
                _ => op_to_const(&ecx, &place.into()),
            };
            debug!(?const_val);

            const_val
        }
        ty::Never
        | ty::Error(_)
        | ty::Foreign(..)
        | ty::Infer(ty::FreshIntTy(_))
        | ty::Infer(ty::FreshFloatTy(_))
        | ty::Projection(..)
        | ty::Param(_)
        | ty::Bound(..)
        | ty::Placeholder(..)
        | ty::Opaque(..)
        | ty::Infer(_)
        | ty::Closure(..)
        | ty::Generator(..)
        | ty::GeneratorWitness(..)
        | ty::FnPtr(_)
        | ty::RawPtr(_)
        | ty::Str
        | ty::Slice(_)
        | ty::Dynamic(..) => bug!("no ValTree should have been created for type {:?}", ty.kind()),
    }
}

#[instrument(skip(ecx), level = "debug")]
fn valtree_into_mplace<'tcx>(
    ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
    place: &mut MPlaceTy<'tcx>,
    valtree: ty::ValTree<'tcx>,
) {
    // This will match on valtree and write the value(s) corresponding to the ValTree
    // inside the place recursively.

    let tcx = ecx.tcx.tcx;
    let ty = place.layout.ty;

    match ty.kind() {
        ty::FnDef(_, _) => {
            ecx.write_immediate(Immediate::Uninit, &place.into()).unwrap();
        }
        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => {
            let scalar_int = valtree.unwrap_leaf();
            debug!("writing trivial valtree {:?} to place {:?}", scalar_int, place);
            ecx.write_immediate(
                Immediate::Scalar(ScalarMaybeUninit::Scalar(scalar_int.into())),
                &place.into(),
            )
            .unwrap();
        }
        ty::Ref(_, inner_ty, _) => {
            let mut pointee_place = create_pointee_place(ecx, *inner_ty, valtree);
            debug!(?pointee_place);

            valtree_into_mplace(ecx, &mut pointee_place, valtree);
            dump_place(ecx, pointee_place.into());
            intern_const_alloc_recursive(ecx, InternKind::Constant, &pointee_place).unwrap();

            let imm = match inner_ty.kind() {
                ty::Slice(_) | ty::Str => {
                    let len = valtree.unwrap_branch().len();
                    let len_scalar =
                        ScalarMaybeUninit::Scalar(Scalar::from_machine_usize(len as u64, &tcx));

                    Immediate::ScalarPair(
                        ScalarMaybeUninit::from_maybe_pointer((*pointee_place).ptr, &tcx),
                        len_scalar,
                    )
                }
                _ => pointee_place.to_ref(&tcx),
            };
            debug!(?imm);

            ecx.write_immediate(imm, &place.into()).unwrap();
        }
        ty::Adt(_, _) | ty::Tuple(_) | ty::Array(_, _) | ty::Str | ty::Slice(_) => {
            let branches = valtree.unwrap_branch();

            // Need to downcast place for enums
            let (place_adjusted, branches, variant_idx) = match ty.kind() {
                ty::Adt(def, _) if def.is_enum() => {
                    // First element of valtree corresponds to variant
                    let scalar_int = branches[0].unwrap_leaf();
                    let variant_idx = VariantIdx::from_u32(scalar_int.try_to_u32().unwrap());
                    let variant = def.variant(variant_idx);
                    debug!(?variant);

                    (
                        place.project_downcast(ecx, variant_idx).unwrap(),
                        &branches[1..],
                        Some(variant_idx),
                    )
                }
                _ => (*place, branches, None),
            };
            debug!(?place_adjusted, ?branches);

            // Create the places (by indexing into `place`) for the fields and fill
            // them recursively
            for (i, inner_valtree) in branches.iter().enumerate() {
                debug!(?i, ?inner_valtree);

                let mut place_inner = match ty.kind() {
                    ty::Str | ty::Slice(_) => ecx.mplace_index(&place, i as u64).unwrap(),
                    _ if !ty.is_sized(ecx.tcx, ty::ParamEnv::empty())
                        && i == branches.len() - 1 =>
                    {
                        // Note: For custom DSTs we need to manually process the last unsized field.
                        // We created a `Pointer` for the `Allocation` of the complete sized version of
                        // the Adt in `create_pointee_place` and now we fill that `Allocation` with the
                        // values in the ValTree. For the unsized field we have to additionally add the meta
                        // data.

                        let (unsized_inner_ty, num_elems) =
                            get_info_on_unsized_field(ty, valtree, tcx);
                        debug!(?unsized_inner_ty);

                        let inner_ty = match ty.kind() {
                            ty::Adt(def, substs) => {
                                def.variant(VariantIdx::from_u32(0)).fields[i].ty(tcx, substs)
                            }
                            ty::Tuple(inner_tys) => inner_tys[i],
                            _ => bug!("unexpected unsized type {:?}", ty),
                        };

                        let inner_layout =
                            tcx.layout_of(ty::ParamEnv::empty().and(inner_ty)).unwrap();
                        debug!(?inner_layout);

                        let offset = place_adjusted.layout.fields.offset(i);
                        place
                            .offset_with_meta(
                                offset,
                                MemPlaceMeta::Meta(Scalar::from_machine_usize(
                                    num_elems as u64,
                                    &tcx,
                                )),
                                inner_layout,
                                &tcx,
                            )
                            .unwrap()
                    }
                    _ => ecx.mplace_field(&place_adjusted, i).unwrap(),
                };

                debug!(?place_inner);
                valtree_into_mplace(ecx, &mut place_inner, *inner_valtree);
                dump_place(&ecx, place_inner.into());
            }

            debug!("dump of place_adjusted:");
            dump_place(ecx, place_adjusted.into());

            if let Some(variant_idx) = variant_idx {
                // don't forget filling the place with the discriminant of the enum
                ecx.write_discriminant(variant_idx, &place.into()).unwrap();
            }

            debug!("dump of place after writing discriminant:");
            dump_place(ecx, place.into());
        }
        _ => bug!("shouldn't have created a ValTree for {:?}", ty),
    }
}

fn dump_place<'tcx>(ecx: &CompileTimeEvalContext<'tcx, 'tcx>, place: PlaceTy<'tcx>) {
    trace!("{:?}", ecx.dump_place(*place));
}