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,
8 use crate::util::pretty::display_allocation;
10 use rustc_errors::ErrorReported;
11 use rustc_hir::def::DefKind;
12 use rustc_middle::mir;
13 use rustc_middle::mir::interpret::ErrorHandled;
14 use rustc_middle::traits::Reveal;
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::{Abi, LayoutOf};
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()),
46 "Unexpected DefKind: {:?}",
47 ecx.tcx.def_kind(cid.instance.def_id())
49 let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
50 assert!(!layout.is_unsized());
51 let ret = ecx.allocate(layout, MemoryKind::Stack)?;
54 with_no_trimmed_paths(|| ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id())));
55 let prom = cid.promoted.map_or_else(String::new, |p| format!("::promoted[{:?}]", p));
56 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
62 StackPopCleanup::None { cleanup: false },
65 // The main interpreter loop.
69 let intern_kind = if cid.promoted.is_some() {
72 match tcx.static_mutability(cid.instance.def_id()) {
73 Some(m) => InternKind::Static(m),
74 None => InternKind::Constant,
77 intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
79 debug!("eval_body_using_ecx done: {:?}", *ret);
83 /// The `InterpCx` is only meant to be used to do field and index projections into constants for
84 /// `simd_shuffle` and const patterns in match arms.
86 /// The function containing the `match` that is currently being analyzed may have generic bounds
87 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
88 /// of a function's generic parameter will require knowledge about the bounds on the generic
89 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
90 pub(super) fn mk_eval_cx<'mir, 'tcx>(
93 param_env: ty::ParamEnv<'tcx>,
94 can_access_statics: bool,
95 ) -> CompileTimeEvalContext<'mir, 'tcx> {
96 debug!("mk_eval_cx: {:?}", param_env);
101 CompileTimeInterpreter::new(tcx.const_eval_limit()),
102 MemoryExtra { can_access_statics },
106 /// This function converts an interpreter value into a constant that is meant for use in the
108 pub(super) fn op_to_const<'tcx>(
109 ecx: &CompileTimeEvalContext<'_, 'tcx>,
111 ) -> ConstValue<'tcx> {
112 // We do not have value optimizations for everything.
113 // Only scalars and slices, since they are very common.
114 // Note that further down we turn scalars of uninitialized bits back to `ByRef`. These can result
115 // from scalar unions that are initialized with one of their zero sized variants. We could
116 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUninit`, but that would affect all
117 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
118 // `Undef` situation.
119 let try_as_immediate = match op.layout.abi {
120 Abi::Scalar(..) => true,
121 Abi::ScalarPair(..) => match op.layout.ty.kind() {
122 ty::Ref(_, inner, _) => match *inner.kind() {
123 ty::Slice(elem) => elem == ecx.tcx.types.u8,
131 let immediate = if try_as_immediate {
132 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
134 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
135 // When we come back from raw const eval, we are always by-ref. The only way our op here is
136 // by-val is if we are in destructure_const, i.e., if this is (a field of) something that we
137 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
138 // structs containing such.
142 // We know `offset` is relative to the allocation, so we can use `into_parts`.
143 let to_const_value = |mplace: &MPlaceTy<'_>| match mplace.ptr.into_parts() {
144 (Some(alloc_id), offset) => {
145 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
146 ConstValue::ByRef { alloc, offset }
149 assert!(mplace.layout.is_zst());
151 offset.bytes() % mplace.layout.align.abi.bytes(),
153 "this MPlaceTy must come from a validated constant, thus we can assume the \
154 alignment is correct",
156 ConstValue::Scalar(Scalar::ZST)
160 Ok(ref mplace) => to_const_value(mplace),
161 // see comment on `let try_as_immediate` above
162 Err(imm) => match *imm {
163 Immediate::Scalar(x) => match x {
164 ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s),
165 ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()),
167 Immediate::ScalarPair(a, b) => {
168 // We know `offset` is relative to the allocation, so we can use `into_parts`.
169 let (data, start) = match ecx.scalar_to_ptr(a.check_init().unwrap()).into_parts() {
170 (Some(alloc_id), offset) => {
171 (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes())
174 ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
180 let len = b.to_machine_usize(ecx).unwrap();
181 let start = start.try_into().unwrap();
182 let len: usize = len.try_into().unwrap();
183 ConstValue::Slice { data, start, end: start + len }
189 fn turn_into_const_value<'tcx>(
191 constant: ConstAlloc<'tcx>,
192 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
193 ) -> ConstValue<'tcx> {
195 let def_id = cid.instance.def.def_id();
196 let is_static = tcx.is_static(def_id);
197 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
199 let mplace = ecx.raw_const_to_mplace(constant).expect(
200 "can only fail if layout computation failed, \
201 which should have given a good error before ever invoking this function",
204 !is_static || cid.promoted.is_some(),
205 "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead"
207 // Turn this into a proper constant.
208 op_to_const(&ecx, &mplace.into())
211 pub fn eval_to_const_value_raw_provider<'tcx>(
213 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
214 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
215 // see comment in eval_to_allocation_raw_provider for what we're doing here
216 if key.param_env.reveal() == Reveal::All {
218 key.param_env = key.param_env.with_user_facing();
219 match tcx.eval_to_const_value_raw(key) {
220 // try again with reveal all as requested
221 Err(ErrorHandled::TooGeneric) => {}
223 other => return other,
227 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
228 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
229 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
230 let ty = key.value.instance.ty(tcx, key.param_env);
231 let substs = match ty.kind() {
232 ty::FnDef(_, substs) => substs,
233 _ => bug!("intrinsic with type {:?}", ty),
235 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
236 let span = tcx.def_span(def_id);
237 let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
238 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
242 tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
245 pub fn eval_to_allocation_raw_provider<'tcx>(
247 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
248 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
249 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
250 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
251 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
252 // computed. For a large percentage of constants that will already have succeeded. Only
253 // associated constants of generic functions will fail due to not enough monomorphization
254 // information being available.
256 // In case we fail in the `UserFacing` variant, we just do the real computation.
257 if key.param_env.reveal() == Reveal::All {
259 key.param_env = key.param_env.with_user_facing();
260 match tcx.eval_to_allocation_raw(key) {
261 // try again with reveal all as requested
262 Err(ErrorHandled::TooGeneric) => {}
264 other => return other,
267 if cfg!(debug_assertions) {
268 // Make sure we format the instance even if we do not print it.
269 // This serves as a regression test against an ICE on printing.
270 // The next two lines concatenated contain some discussion:
271 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
272 // subject/anon_const_instance_printing/near/135980032
273 let instance = with_no_trimmed_paths(|| key.value.instance.to_string());
274 trace!("const eval: {:?} ({})", key, instance);
278 let def = cid.instance.def.with_opt_param();
280 if let Some(def) = def.as_local() {
281 if tcx.has_typeck_results(def.did) {
282 if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
283 return Err(ErrorHandled::Reported(error_reported));
286 if !tcx.is_mir_available(def.did) {
287 tcx.sess.delay_span_bug(
288 tcx.def_span(def.did),
289 &format!("no MIR body is available for {:?}", def.did),
291 return Err(ErrorHandled::Reported(ErrorReported {}));
293 if let Some(error_reported) = tcx.mir_const_qualif_opt_const_arg(def).error_occured {
294 return Err(ErrorHandled::Reported(error_reported));
298 let is_static = tcx.is_static(def.did);
300 let mut ecx = InterpCx::new(
302 tcx.def_span(def.did),
304 CompileTimeInterpreter::new(tcx.const_eval_limit()),
305 // Statics (and promoteds inside statics) may access other statics, because unlike consts
306 // they do not have to behave "as if" they were evaluated at runtime.
307 MemoryExtra { can_access_statics: is_static },
310 let res = ecx.load_mir(cid.instance.def, cid.promoted);
311 match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
313 let err = ConstEvalErr::new(&ecx, error, None);
314 // Some CTFE errors raise just a lint, not a hard error; see
315 // <https://github.com/rust-lang/rust/issues/71800>.
316 let is_hard_err = if let Some(def) = def.as_local() {
317 // (Associated) consts only emit a lint, since they might be unused.
318 !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
319 // check if the inner InterpError is hard
320 || err.error.is_hard_err()
322 // use of broken constant from other crate: always an error
327 let msg = if is_static {
328 Cow::from("could not evaluate static initializer")
330 // If the current item has generics, we'd like to enrich the message with the
331 // instance and its substs: to show the actual compile-time values, in addition to
332 // the expression, leading to the const eval error.
333 let instance = &key.value.instance;
334 if !instance.substs.is_empty() {
335 let instance = with_no_trimmed_paths(|| instance.to_string());
336 let msg = format!("evaluation of `{}` failed", instance);
339 Cow::from("evaluation of constant value failed")
343 Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), &msg))
345 let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
346 Err(err.report_as_lint(
347 tcx.at(tcx.def_span(def.did)),
348 "any use of this value will cause an error",
355 // Since evaluation had no errors, validate the resulting constant.
356 // This is a separate `try` block to provide more targeted error reporting.
357 let validation = try {
358 let mut ref_tracking = RefTracking::new(mplace);
359 let mut inner = false;
360 while let Some((mplace, path)) = ref_tracking.todo.pop() {
361 let mode = match tcx.static_mutability(cid.instance.def_id()) {
362 Some(_) if cid.promoted.is_some() => {
363 // Promoteds in statics are allowed to point to statics.
364 CtfeValidationMode::Const { inner, allow_static_ptrs: true }
366 Some(_) => CtfeValidationMode::Regular, // a `static`
367 None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
369 ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
373 let alloc_id = mplace.ptr.provenance.unwrap();
374 if let Err(error) = validation {
375 // Validation failed, report an error. This is always a hard error.
376 let err = ConstEvalErr::new(&ecx, error, None);
377 Err(err.struct_error(
379 "it is undefined behavior to use this value",
381 diag.note(note_on_undefined_behavior_error());
383 "the raw bytes of the constant ({}",
386 ecx.tcx.global_alloc(alloc_id).unwrap_memory()
393 // Convert to raw constant
394 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })