1 use super::{CompileTimeEvalContext, CompileTimeInterpreter, ConstEvalErr, MemoryExtra};
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_errors::ErrorReported;
10 use rustc_hir::def::DefKind;
11 use rustc_middle::mir;
12 use rustc_middle::mir::interpret::ErrorHandled;
13 use rustc_middle::mir::pretty::display_allocation;
14 use rustc_middle::traits::Reveal;
15 use rustc_middle::ty::layout::LayoutOf;
16 use rustc_middle::ty::print::with_no_trimmed_paths;
17 use rustc_middle::ty::{self, subst::Subst, TyCtxt};
18 use rustc_span::source_map::Span;
19 use rustc_target::abi::Abi;
21 use std::convert::TryInto;
23 pub fn note_on_undefined_behavior_error() -> &'static str {
24 "The rules on what exactly is undefined behavior aren't clear, \
25 so this check might be overzealous. Please open an issue on the rustc \
26 repository if you believe it should not be considered undefined behavior."
29 // Returns a pointer to where the result lives
30 fn eval_body_using_ecx<'mir, 'tcx>(
31 ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
33 body: &'mir mir::Body<'tcx>,
34 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
35 debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
38 cid.promoted.is_some()
40 ecx.tcx.def_kind(cid.instance.def_id()),
45 | DefKind::InlineConst
48 "Unexpected DefKind: {:?}",
49 ecx.tcx.def_kind(cid.instance.def_id())
51 let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
52 assert!(!layout.is_unsized());
53 let ret = ecx.allocate(layout, MemoryKind::Stack)?;
56 "eval_body_using_ecx: pushing stack frame for global: {}{}",
57 with_no_trimmed_paths(|| ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()))),
58 cid.promoted.map_or_else(String::new, |p| format!("::promoted[{:?}]", p))
65 StackPopCleanup::None { cleanup: false },
68 // The main interpreter loop.
72 let intern_kind = if cid.promoted.is_some() {
75 match tcx.static_mutability(cid.instance.def_id()) {
76 Some(m) => InternKind::Static(m),
77 None => InternKind::Constant,
80 intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
82 debug!("eval_body_using_ecx done: {:?}", *ret);
86 /// The `InterpCx` is only meant to be used to do field and index projections into constants for
87 /// `simd_shuffle` and const patterns in match arms.
89 /// The function containing the `match` that is currently being analyzed may have generic bounds
90 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
91 /// of a function's generic parameter will require knowledge about the bounds on the generic
92 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
93 pub(super) fn mk_eval_cx<'mir, 'tcx>(
96 param_env: ty::ParamEnv<'tcx>,
97 can_access_statics: bool,
98 ) -> CompileTimeEvalContext<'mir, 'tcx> {
99 debug!("mk_eval_cx: {:?}", param_env);
104 CompileTimeInterpreter::new(tcx.const_eval_limit()),
105 MemoryExtra { can_access_statics },
109 /// This function converts an interpreter value into a constant that is meant for use in the
111 pub(super) fn op_to_const<'tcx>(
112 ecx: &CompileTimeEvalContext<'_, 'tcx>,
114 ) -> ConstValue<'tcx> {
115 // We do not have value optimizations for everything.
116 // Only scalars and slices, since they are very common.
117 // Note that further down we turn scalars of uninitialized bits back to `ByRef`. These can result
118 // from scalar unions that are initialized with one of their zero sized variants. We could
119 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUninit`, but that would affect all
120 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
121 // `Undef` situation.
122 let try_as_immediate = match op.layout.abi {
123 Abi::Scalar(..) => true,
124 Abi::ScalarPair(..) => match op.layout.ty.kind() {
125 ty::Ref(_, inner, _) => match *inner.kind() {
126 ty::Slice(elem) => elem == ecx.tcx.types.u8,
134 let immediate = if try_as_immediate {
135 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
137 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
138 // When we come back from raw const eval, we are always by-ref. The only way our op here is
139 // by-val is if we are in destructure_const, i.e., if this is (a field of) something that we
140 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
141 // structs containing such.
145 // We know `offset` is relative to the allocation, so we can use `into_parts`.
146 let to_const_value = |mplace: &MPlaceTy<'_>| match mplace.ptr.into_parts() {
147 (Some(alloc_id), offset) => {
148 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
149 ConstValue::ByRef { alloc, offset }
152 assert!(mplace.layout.is_zst());
154 offset.bytes() % mplace.layout.align.abi.bytes(),
156 "this MPlaceTy must come from a validated constant, thus we can assume the \
157 alignment is correct",
159 ConstValue::Scalar(Scalar::ZST)
163 Ok(ref mplace) => to_const_value(mplace),
164 // see comment on `let try_as_immediate` above
165 Err(imm) => match *imm {
166 Immediate::Scalar(x) => match x {
167 ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s),
168 ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()),
170 Immediate::ScalarPair(a, b) => {
171 // We know `offset` is relative to the allocation, so we can use `into_parts`.
172 let (data, start) = match ecx.scalar_to_ptr(a.check_init().unwrap()).into_parts() {
173 (Some(alloc_id), offset) => {
174 (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes())
177 ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
183 let len = b.to_machine_usize(ecx).unwrap();
184 let start = start.try_into().unwrap();
185 let len: usize = len.try_into().unwrap();
186 ConstValue::Slice { data, start, end: start + len }
192 fn turn_into_const_value<'tcx>(
194 constant: ConstAlloc<'tcx>,
195 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
196 ) -> ConstValue<'tcx> {
198 let def_id = cid.instance.def.def_id();
199 let is_static = tcx.is_static(def_id);
200 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
202 let mplace = ecx.raw_const_to_mplace(constant).expect(
203 "can only fail if layout computation failed, \
204 which should have given a good error before ever invoking this function",
207 !is_static || cid.promoted.is_some(),
208 "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead"
210 // Turn this into a proper constant.
211 op_to_const(&ecx, &mplace.into())
214 pub fn eval_to_const_value_raw_provider<'tcx>(
216 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
217 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
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 substs = match ty.kind() {
235 ty::FnDef(_, substs) => substs,
236 _ => bug!("intrinsic with type {:?}", ty),
238 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
239 let span = tcx.def_span(def_id);
240 let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
241 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
245 tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
248 pub fn eval_to_allocation_raw_provider<'tcx>(
250 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
251 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
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();
283 if let Some(def) = def.as_local() {
284 if tcx.has_typeck_results(def.did) {
285 if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
286 return Err(ErrorHandled::Reported(error_reported));
289 if !tcx.is_mir_available(def.did) {
290 tcx.sess.delay_span_bug(
291 tcx.def_span(def.did),
292 &format!("no MIR body is available for {:?}", def.did),
294 return Err(ErrorHandled::Reported(ErrorReported {}));
296 if let Some(error_reported) = tcx.mir_const_qualif_opt_const_arg(def).error_occured {
297 return Err(ErrorHandled::Reported(error_reported));
301 let is_static = tcx.is_static(def.did);
303 let mut ecx = InterpCx::new(
305 tcx.def_span(def.did),
307 CompileTimeInterpreter::new(tcx.const_eval_limit()),
308 // Statics (and promoteds inside statics) may access other statics, because unlike consts
309 // they do not have to behave "as if" they were evaluated at runtime.
310 MemoryExtra { can_access_statics: is_static },
313 let res = ecx.load_mir(cid.instance.def, cid.promoted);
314 match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
316 let err = ConstEvalErr::new(&ecx, error, None);
317 // Some CTFE errors raise just a lint, not a hard error; see
318 // <https://github.com/rust-lang/rust/issues/71800>.
319 let is_hard_err = if let Some(def) = def.as_local() {
320 // (Associated) consts only emit a lint, since they might be unused.
321 !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
322 // check if the inner InterpError is hard
323 || err.error.is_hard_err()
325 // use of broken constant from other crate: always an error
330 let msg = if is_static {
331 Cow::from("could not evaluate static initializer")
333 // If the current item has generics, we'd like to enrich the message with the
334 // instance and its substs: to show the actual compile-time values, in addition to
335 // the expression, leading to the const eval error.
336 let instance = &key.value.instance;
337 if !instance.substs.is_empty() {
338 let instance = with_no_trimmed_paths(|| instance.to_string());
339 let msg = format!("evaluation of `{}` failed", instance);
342 Cow::from("evaluation of constant value failed")
346 Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), &msg))
348 let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
349 Err(err.report_as_lint(
350 tcx.at(tcx.def_span(def.did)),
351 "any use of this value will cause an error",
358 // Since evaluation had no errors, validate the resulting constant.
359 // This is a separate `try` block to provide more targeted error reporting.
360 let validation = try {
361 let mut ref_tracking = RefTracking::new(mplace);
362 let mut inner = false;
363 while let Some((mplace, path)) = ref_tracking.todo.pop() {
364 let mode = match tcx.static_mutability(cid.instance.def_id()) {
365 Some(_) if cid.promoted.is_some() => {
366 // Promoteds in statics are allowed to point to statics.
367 CtfeValidationMode::Const { inner, allow_static_ptrs: true }
369 Some(_) => CtfeValidationMode::Regular, // a `static`
370 None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
372 ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
376 let alloc_id = mplace.ptr.provenance.unwrap();
377 if let Err(error) = validation {
378 // Validation failed, report an error. This is always a hard error.
379 let err = ConstEvalErr::new(&ecx, error, None);
380 Err(err.struct_error(
382 "it is undefined behavior to use this value",
384 diag.note(note_on_undefined_behavior_error());
386 "the raw bytes of the constant ({}",
389 ecx.tcx.global_alloc(alloc_id).unwrap_memory()
396 // Convert to raw constant
397 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })