1 use super::{CompileTimeEvalContext, CompileTimeInterpreter, ConstEvalErr};
2 use crate::interpret::eval_nullary_intrinsic;
3 use crate::interpret::{
4 intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, CtfeValidationMode, GlobalId,
5 Immediate, InternKind, InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking, Scalar,
6 ScalarMaybeUninit, StackPopCleanup,
9 use rustc_hir::def::DefKind;
10 use rustc_middle::mir;
11 use rustc_middle::mir::interpret::ErrorHandled;
12 use rustc_middle::mir::pretty::display_allocation;
13 use rustc_middle::traits::Reveal;
14 use rustc_middle::ty::layout::LayoutOf;
15 use rustc_middle::ty::print::with_no_trimmed_paths;
16 use rustc_middle::ty::{self, subst::Subst, TyCtxt};
17 use rustc_span::source_map::Span;
18 use rustc_target::abi::{self, Abi};
20 use std::convert::TryInto;
22 pub fn note_on_undefined_behavior_error() -> &'static str {
23 "The rules on what exactly is undefined behavior aren't clear, \
24 so this check might be overzealous. Please open an issue on the rustc \
25 repository if you believe it should not be considered undefined behavior."
28 // Returns a pointer to where the result lives
29 fn eval_body_using_ecx<'mir, 'tcx>(
30 ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
32 body: &'mir mir::Body<'tcx>,
33 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
34 debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
37 cid.promoted.is_some()
39 ecx.tcx.def_kind(cid.instance.def_id()),
44 | DefKind::InlineConst
47 "Unexpected DefKind: {:?}",
48 ecx.tcx.def_kind(cid.instance.def_id())
50 let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
51 assert!(!layout.is_unsized());
52 let ret = ecx.allocate(layout, MemoryKind::Stack)?;
55 "eval_body_using_ecx: pushing stack frame for global: {}{}",
56 with_no_trimmed_paths!(ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()))),
57 cid.promoted.map_or_else(String::new, |p| format!("::promoted[{:?}]", p))
64 StackPopCleanup::Root { cleanup: false },
67 // The main interpreter loop.
71 let intern_kind = if cid.promoted.is_some() {
74 match tcx.static_mutability(cid.instance.def_id()) {
75 Some(m) => InternKind::Static(m),
76 None => InternKind::Constant,
79 intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
81 debug!("eval_body_using_ecx done: {:?}", *ret);
85 /// The `InterpCx` is only meant to be used to do field and index projections into constants for
86 /// `simd_shuffle` and const patterns in match arms.
88 /// The function containing the `match` that is currently being analyzed may have generic bounds
89 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
90 /// of a function's generic parameter will require knowledge about the bounds on the generic
91 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
92 pub(super) fn mk_eval_cx<'mir, 'tcx>(
95 param_env: ty::ParamEnv<'tcx>,
96 can_access_statics: bool,
97 ) -> CompileTimeEvalContext<'mir, 'tcx> {
98 debug!("mk_eval_cx: {:?}", param_env);
103 CompileTimeInterpreter::new(tcx.const_eval_limit(), can_access_statics),
107 /// This function converts an interpreter value into a constant that is meant for use in the
109 pub(super) fn op_to_const<'tcx>(
110 ecx: &CompileTimeEvalContext<'_, 'tcx>,
112 ) -> ConstValue<'tcx> {
113 // We do not have value optimizations for everything.
114 // Only scalars and slices, since they are very common.
115 // Note that further down we turn scalars of uninitialized bits back to `ByRef`. These can result
116 // from scalar unions that are initialized with one of their zero sized variants. We could
117 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUninit`, but that would affect all
118 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
119 // `Undef` situation.
120 let try_as_immediate = match op.layout.abi {
121 Abi::Scalar(abi::Scalar::Initialized { .. }) => true,
122 Abi::ScalarPair(..) => match op.layout.ty.kind() {
123 ty::Ref(_, inner, _) => match *inner.kind() {
124 ty::Slice(elem) => elem == ecx.tcx.types.u8,
132 let immediate = if try_as_immediate {
133 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
135 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
136 // When we come back from raw const eval, we are always by-ref. The only way our op here is
137 // by-val is if we are in destructure_const, i.e., if this is (a field of) something that we
138 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
139 // structs containing such.
143 // We know `offset` is relative to the allocation, so we can use `into_parts`.
144 let to_const_value = |mplace: &MPlaceTy<'_>| match mplace.ptr.into_parts() {
145 (Some(alloc_id), offset) => {
146 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
147 ConstValue::ByRef { alloc, offset }
150 assert!(mplace.layout.is_zst());
152 offset.bytes() % mplace.layout.align.abi.bytes(),
154 "this MPlaceTy must come from a validated constant, thus we can assume the \
155 alignment is correct",
157 ConstValue::Scalar(Scalar::ZST)
161 Ok(ref mplace) => to_const_value(mplace),
162 // see comment on `let try_as_immediate` above
163 Err(imm) => match *imm {
164 Immediate::Scalar(x) => match x {
165 ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s),
166 ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()),
168 Immediate::ScalarPair(a, b) => {
169 // We know `offset` is relative to the allocation, so we can use `into_parts`.
171 match ecx.scalar_to_ptr(a.check_init().unwrap()).unwrap().into_parts() {
172 (Some(alloc_id), offset) => {
173 (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes())
176 ecx.tcx.intern_const_alloc(
177 Allocation::from_bytes_byte_aligned_immutable(b"" as &[u8]),
182 let len = b.to_machine_usize(ecx).unwrap();
183 let start = start.try_into().unwrap();
184 let len: usize = len.try_into().unwrap();
185 ConstValue::Slice { data, start, end: start + len }
191 fn turn_into_const_value<'tcx>(
193 constant: ConstAlloc<'tcx>,
194 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
195 ) -> ConstValue<'tcx> {
197 let def_id = cid.instance.def.def_id();
198 let is_static = tcx.is_static(def_id);
199 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
201 let mplace = ecx.raw_const_to_mplace(constant).expect(
202 "can only fail if layout computation failed, \
203 which should have given a good error before ever invoking this function",
206 !is_static || cid.promoted.is_some(),
207 "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead"
209 // Turn this into a proper constant.
210 op_to_const(&ecx, &mplace.into())
213 pub fn eval_to_const_value_raw_provider<'tcx>(
215 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
216 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
217 assert!(key.param_env.is_const());
218 // see comment in eval_to_allocation_raw_provider for what we're doing here
219 if key.param_env.reveal() == Reveal::All {
221 key.param_env = key.param_env.with_user_facing();
222 match tcx.eval_to_const_value_raw(key) {
223 // try again with reveal all as requested
224 Err(ErrorHandled::TooGeneric) => {}
226 other => return other,
230 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
231 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
232 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
233 let ty = key.value.instance.ty(tcx, key.param_env);
234 let ty::FnDef(_, substs) = ty.kind() else {
235 bug!("intrinsic with type {:?}", ty);
237 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
238 let span = tcx.def_span(def_id);
239 let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
240 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
244 tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
247 pub fn eval_to_allocation_raw_provider<'tcx>(
249 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
250 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
251 assert!(key.param_env.is_const());
252 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
253 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
254 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
255 // computed. For a large percentage of constants that will already have succeeded. Only
256 // associated constants of generic functions will fail due to not enough monomorphization
257 // information being available.
259 // In case we fail in the `UserFacing` variant, we just do the real computation.
260 if key.param_env.reveal() == Reveal::All {
262 key.param_env = key.param_env.with_user_facing();
263 match tcx.eval_to_allocation_raw(key) {
264 // try again with reveal all as requested
265 Err(ErrorHandled::TooGeneric) => {}
267 other => return other,
270 if cfg!(debug_assertions) {
271 // Make sure we format the instance even if we do not print it.
272 // This serves as a regression test against an ICE on printing.
273 // The next two lines concatenated contain some discussion:
274 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
275 // subject/anon_const_instance_printing/near/135980032
276 let instance = with_no_trimmed_paths!(key.value.instance.to_string());
277 trace!("const eval: {:?} ({})", key, instance);
281 let def = cid.instance.def.with_opt_param();
282 let is_static = tcx.is_static(def.did);
284 let mut ecx = InterpCx::new(
286 tcx.def_span(def.did),
288 // Statics (and promoteds inside statics) may access other statics, because unlike consts
289 // they do not have to behave "as if" they were evaluated at runtime.
290 CompileTimeInterpreter::new(tcx.const_eval_limit(), /*can_access_statics:*/ is_static),
293 let res = ecx.load_mir(cid.instance.def, cid.promoted);
294 match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
296 let err = ConstEvalErr::new(&ecx, error, None);
297 // Some CTFE errors raise just a lint, not a hard error; see
298 // <https://github.com/rust-lang/rust/issues/71800>.
299 let is_hard_err = if let Some(def) = def.as_local() {
300 // (Associated) consts only emit a lint, since they might be unused.
301 !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
302 // check if the inner InterpError is hard
303 || err.error.is_hard_err()
305 // use of broken constant from other crate: always an error
310 let msg = if is_static {
311 Cow::from("could not evaluate static initializer")
313 // If the current item has generics, we'd like to enrich the message with the
314 // instance and its substs: to show the actual compile-time values, in addition to
315 // the expression, leading to the const eval error.
316 let instance = &key.value.instance;
317 if !instance.substs.is_empty() {
318 let instance = with_no_trimmed_paths!(instance.to_string());
319 let msg = format!("evaluation of `{}` failed", instance);
322 Cow::from("evaluation of constant value failed")
326 Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), &msg))
328 let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
329 Err(err.report_as_lint(
330 tcx.at(tcx.def_span(def.did)),
331 "any use of this value will cause an error",
338 // Since evaluation had no errors, validate the resulting constant.
339 // This is a separate `try` block to provide more targeted error reporting.
340 let validation = try {
341 let mut ref_tracking = RefTracking::new(mplace);
342 let mut inner = false;
343 while let Some((mplace, path)) = ref_tracking.todo.pop() {
344 let mode = match tcx.static_mutability(cid.instance.def_id()) {
345 Some(_) if cid.promoted.is_some() => {
346 // Promoteds in statics are allowed to point to statics.
347 CtfeValidationMode::Const { inner, allow_static_ptrs: true }
349 Some(_) => CtfeValidationMode::Regular, // a `static`
350 None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
352 ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
356 let alloc_id = mplace.ptr.provenance.unwrap();
357 if let Err(error) = validation {
358 // Validation failed, report an error. This is always a hard error.
359 let err = ConstEvalErr::new(&ecx, error, None);
360 Err(err.struct_error(
362 "it is undefined behavior to use this value",
364 diag.note(note_on_undefined_behavior_error());
366 "the raw bytes of the constant ({}",
369 ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner()
375 // Convert to raw constant
376 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })