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
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_middle::mir::interpret::{EvalToValTreeResult, GlobalId};
use rustc_middle::ty::layout::{LayoutCx, LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
use rustc_middle::{bug, mir};
use rustc_span::DUMMY_SP;
use rustc_target::abi::{Abi, VariantIdx};
use tracing::{debug, instrument, trace};

use super::eval_queries::{mk_eval_cx_to_read_const_val, op_to_const};
use super::machine::CompileTimeInterpCx;
use super::{ValTreeCreationError, ValTreeCreationResult, VALTREE_MAX_NODES};
use crate::const_eval::CanAccessMutGlobal;
use crate::errors::MaxNumNodesInConstErr;
use crate::interpret::{
    intern_const_alloc_recursive, ImmTy, Immediate, InternKind, MPlaceTy, MemPlaceMeta, MemoryKind,
    PlaceTy, Projectable, Scalar,
};

#[instrument(skip(ecx), level = "debug")]
fn branches<'tcx>(
    ecx: &CompileTimeInterpCx<'tcx>,
    place: &MPlaceTy<'tcx>,
    n: usize,
    variant: Option<VariantIdx>,
    num_nodes: &mut usize,
) -> ValTreeCreationResult<'tcx> {
    let place = match variant {
        Some(variant) => ecx.project_downcast(place, variant).unwrap(),
        None => place.clone(),
    };
    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.project_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: &CompileTimeInterpCx<'tcx>,
    place: &MPlaceTy<'tcx>,
    num_nodes: &mut usize,
) -> ValTreeCreationResult<'tcx> {
    let n = place.len(ecx).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.project_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")]
fn const_to_valtree_inner<'tcx>(
    ecx: &CompileTimeInterpCx<'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 val = ecx.read_immediate(place)?;
            let val = val.to_scalar_int().unwrap();
            *num_nodes += 1;

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

        ty::Pat(base, ..) => {
            let mut place = place.clone();
            // The valtree of the base type is the same as the valtree of the pattern type.
            // Since the returned valtree does not contain the type or layout, we can just
            // switch to the base type.
            place.layout = ecx.layout_of(*base).unwrap();
            ensure_sufficient_stack(|| const_to_valtree_inner(ecx, &place, num_nodes))
        },


        ty::RawPtr(_, _) => {
            // Not all raw pointers are allowed, as we cannot properly test them for
            // equality at compile-time (see `ptr_guaranteed_cmp`).
            // However we allow those that are just integers in disguise.
            // First, get the pointer. Remember it might be wide!
            let val = ecx.read_immediate(place)?;
            // We could allow wide raw pointers where both sides are integers in the future,
            // but for now we reject them.
            if matches!(val.layout.abi, Abi::ScalarPair(..)) {
                return Err(ValTreeCreationError::NonSupportedType(ty));
            }
            let val = val.to_scalar();
            // We are in the CTFE machine, so ptr-to-int casts will fail.
            // This can only be `Ok` if `val` already is an integer.
            let Ok(val) = val.try_to_scalar_int() else {
                return Err(ValTreeCreationError::NonSupportedType(ty));
            };
            // It's just a ScalarInt!
            Ok(ty::ValTree::Leaf(val))
        }

        // Technically we could allow function pointers (represented as `ty::Instance`), but this is not guaranteed to
        // agree with runtime equality tests.
        ty::FnPtr(..) => Err(ValTreeCreationError::NonSupportedType(ty)),

        ty::Ref(_, _, _)  => {
            let derefd_place = ecx.deref_pointer(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 StructuralPartialEq` trait objects in the future,
        // but it is unclear if this is useful.
        ty::Dynamic(..) => Err(ValTreeCreationError::NonSupportedType(ty)),

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

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

            let variant = ecx.read_discriminant(place)?;
            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(_))
        // FIXME(oli-obk): we could look behind opaque types
        | ty::Alias(..)
        | ty::Param(_)
        | ty::Bound(..)
        | ty::Placeholder(..)
        | ty::Infer(_)
        // FIXME(oli-obk): we can probably encode closures just like structs
        | ty::Closure(..)
        | ty::CoroutineClosure(..)
        | ty::Coroutine(..)
        | ty::CoroutineWitness(..) => Err(ValTreeCreationError::NonSupportedType(ty)),
    }
}

/// Valtrees don't store the `MemPlaceMeta` that all dynamically sized values have in the interpreter.
/// This function reconstructs it.
fn reconstruct_place_meta<'tcx>(
    layout: TyAndLayout<'tcx>,
    valtree: ty::ValTree<'tcx>,
    tcx: TyCtxt<'tcx>,
) -> MemPlaceMeta {
    if layout.is_sized() {
        return MemPlaceMeta::None;
    }

    let mut last_valtree = valtree;
    // Traverse the type, and update `last_valtree` as we go.
    let tail = tcx.struct_tail_raw(
        layout.ty,
        |ty| ty,
        || {
            let branches = last_valtree.unwrap_branch();
            last_valtree = *branches.last().unwrap();
            debug!(?branches, ?last_valtree);
        },
    );
    // Sanity-check that we got a tail we support.
    match tail.kind() {
        ty::Slice(..) | ty::Str => {}
        _ => bug!("unsized tail of a valtree must be Slice or Str"),
    };

    // Get the number of elements in the unsized field.
    let num_elems = last_valtree.unwrap_branch().len();
    MemPlaceMeta::Meta(Scalar::from_target_usize(num_elems as u64, &tcx))
}

#[instrument(skip(ecx), level = "debug", ret)]
fn create_valtree_place<'tcx>(
    ecx: &mut CompileTimeInterpCx<'tcx>,
    layout: TyAndLayout<'tcx>,
    valtree: ty::ValTree<'tcx>,
) -> MPlaceTy<'tcx> {
    let meta = reconstruct_place_meta(layout, valtree, ecx.tcx.tcx);
    ecx.allocate_dyn(layout, MemoryKind::Stack, meta).unwrap()
}

/// Evaluates a constant and turns it into a type-level constant value.
pub(crate) fn eval_to_valtree<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    cid: GlobalId<'tcx>,
) -> EvalToValTreeResult<'tcx> {
    let const_alloc = tcx.eval_to_allocation_raw(param_env.and(cid))?;

    // FIXME Need to provide a span to `eval_to_valtree`
    let ecx = mk_eval_cx_to_read_const_val(
        tcx,
        DUMMY_SP,
        param_env,
        // It is absolutely crucial for soundness that
        // we do not read from mutable memory.
        CanAccessMutGlobal::No,
    );
    let place = ecx.raw_const_to_mplace(const_alloc).unwrap();
    debug!(?place);

    let mut num_nodes = 0;
    let valtree_result = const_to_valtree_inner(&ecx, &place, &mut num_nodes);

    match valtree_result {
        Ok(valtree) => Ok(Ok(valtree)),
        Err(err) => {
            let did = cid.instance.def_id();
            let global_const_id = cid.display(tcx);
            let span = tcx.hir().span_if_local(did);
            match err {
                ValTreeCreationError::NodesOverflow => {
                    let handled =
                        tcx.dcx().emit_err(MaxNumNodesInConstErr { span, global_const_id });
                    Err(handled.into())
                }
                ValTreeCreationError::NonSupportedType(ty) => Ok(Err(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", ret)]
pub fn valtree_to_const_value<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env_ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
    valtree: ty::ValTree<'tcx>,
) -> mir::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();

    match *ty.kind() {
        ty::FnDef(..) => {
            assert!(valtree.unwrap_branch().is_empty());
            mir::ConstValue::ZeroSized
        }
        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char | ty::RawPtr(_, _) => {
            match valtree {
                ty::ValTree::Leaf(scalar_int) => mir::ConstValue::Scalar(Scalar::Int(scalar_int)),
                ty::ValTree::Branch(_) => bug!(
                    "ValTrees for Bool, Int, Uint, Float, Char or RawPtr should have the form ValTree::Leaf"
                ),
            }
        }
        ty::Pat(ty, _) => valtree_to_const_value(tcx, param_env.and(ty), valtree),
        ty::Ref(_, inner_ty, _) => {
            let mut ecx =
                mk_eval_cx_to_read_const_val(tcx, DUMMY_SP, param_env, CanAccessMutGlobal::No);
            let imm = valtree_to_ref(&mut ecx, valtree, inner_ty);
            let imm = ImmTy::from_immediate(imm, tcx.layout_of(param_env_ty).unwrap());
            op_to_const(&ecx, &imm.into(), /* for diagnostics */ false)
        }
        ty::Tuple(_) | ty::Array(_, _) | ty::Adt(..) => {
            let layout = tcx.layout_of(param_env_ty).unwrap();
            if layout.is_zst() {
                // Fast path to avoid some allocations.
                return mir::ConstValue::ZeroSized;
            }
            if layout.abi.is_scalar()
                && (matches!(ty.kind(), ty::Tuple(_))
                    || matches!(ty.kind(), ty::Adt(def, _) if def.is_struct()))
            {
                // A Scalar tuple/struct; we can avoid creating an allocation.
                let branches = valtree.unwrap_branch();
                // Find the non-ZST field. (There can be aligned ZST!)
                for (i, &inner_valtree) in branches.iter().enumerate() {
                    let field = layout.field(&LayoutCx { tcx, param_env }, i);
                    if !field.is_zst() {
                        return valtree_to_const_value(tcx, param_env.and(field.ty), inner_valtree);
                    }
                }
                bug!("could not find non-ZST field during in {layout:#?}");
            }

            let mut ecx =
                mk_eval_cx_to_read_const_val(tcx, DUMMY_SP, param_env, CanAccessMutGlobal::No);

            // Need to create a place for this valtree.
            let place = create_valtree_place(&mut ecx, layout, valtree);

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

            op_to_const(&ecx, &place.into(), /* for diagnostics */ false)
        }
        ty::Never
        | ty::Error(_)
        | ty::Foreign(..)
        | ty::Infer(ty::FreshIntTy(_))
        | ty::Infer(ty::FreshFloatTy(_))
        | ty::Alias(..)
        | ty::Param(_)
        | ty::Bound(..)
        | ty::Placeholder(..)
        | ty::Infer(_)
        | ty::Closure(..)
        | ty::CoroutineClosure(..)
        | ty::Coroutine(..)
        | ty::CoroutineWitness(..)
        | ty::FnPtr(..)
        | ty::Str
        | ty::Slice(_)
        | ty::Dynamic(..) => bug!("no ValTree should have been created for type {:?}", ty.kind()),
    }
}

/// Put a valtree into memory and return a reference to that.
fn valtree_to_ref<'tcx>(
    ecx: &mut CompileTimeInterpCx<'tcx>,
    valtree: ty::ValTree<'tcx>,
    pointee_ty: Ty<'tcx>,
) -> Immediate {
    let pointee_place = create_valtree_place(ecx, ecx.layout_of(pointee_ty).unwrap(), valtree);
    debug!(?pointee_place);

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

    pointee_place.to_ref(&ecx.tcx)
}

#[instrument(skip(ecx), level = "debug")]
fn valtree_into_mplace<'tcx>(
    ecx: &mut CompileTimeInterpCx<'tcx>,
    place: &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 ty = place.layout.ty;

    match ty.kind() {
        ty::FnDef(_, _) => {
            // Zero-sized type, nothing to do.
        }
        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char | ty::RawPtr(..) => {
            let scalar_int = valtree.unwrap_leaf();
            debug!("writing trivial valtree {:?} to place {:?}", scalar_int, place);
            ecx.write_immediate(Immediate::Scalar(scalar_int.into()), place).unwrap();
        }
        ty::Ref(_, inner_ty, _) => {
            let imm = valtree_to_ref(ecx, valtree, *inner_ty);
            debug!(?imm);
            ecx.write_immediate(imm, place).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.to_u32());
                    let variant = def.variant(variant_idx);
                    debug!(?variant);

                    (
                        ecx.project_downcast(place, variant_idx).unwrap(),
                        &branches[1..],
                        Some(variant_idx),
                    )
                }
                _ => (place.clone(), 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 place_inner = match ty.kind() {
                    ty::Str | ty::Slice(_) | ty::Array(..) => {
                        ecx.project_index(place, i as u64).unwrap()
                    }
                    _ => ecx.project_field(&place_adjusted, i).unwrap(),
                };

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

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

            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).unwrap();
            }

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

fn dump_place<'tcx>(ecx: &CompileTimeInterpCx<'tcx>, place: &MPlaceTy<'tcx>) {
    trace!("{:?}", ecx.dump_place(&PlaceTy::from(place.clone())));
}