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,
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 const NOTE_ON_UNDEFINED_BEHAVIOR_ERROR: &str = "The rules on what exactly is undefined behavior aren't clear, \
23 so this check might be overzealous. Please open an issue on the rustc \
24 repository if you believe it should not be considered undefined behavior.";
26 // Returns a pointer to where the result lives
27 fn eval_body_using_ecx<'mir, 'tcx>(
28 ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
30 body: &'mir mir::Body<'tcx>,
31 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
32 debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
35 cid.promoted.is_some()
37 ecx.tcx.def_kind(cid.instance.def_id()),
42 | DefKind::InlineConst
45 "Unexpected DefKind: {:?}",
46 ecx.tcx.def_kind(cid.instance.def_id())
48 let layout = ecx.layout_of(body.bound_return_ty().subst(tcx, cid.instance.substs))?;
49 assert!(!layout.is_unsized());
50 let ret = ecx.allocate(layout, MemoryKind::Stack)?;
53 "eval_body_using_ecx: pushing stack frame for global: {}{}",
54 with_no_trimmed_paths!(ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()))),
55 cid.promoted.map_or_else(String::new, |p| format!("::promoted[{:?}]", p))
62 StackPopCleanup::Root { 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(), can_access_statics),
105 /// This function converts an interpreter value into a constant that is meant for use in the
107 #[instrument(skip(ecx), level = "debug")]
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(abi::Scalar::Initialized { .. }) => 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_mir_constant, 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.
144 // We know `offset` is relative to the allocation, so we can use `into_parts`.
145 let to_const_value = |mplace: &MPlaceTy<'_>| {
146 debug!("to_const_value(mplace: {:?})", mplace);
147 match mplace.ptr.into_parts() {
148 (Some(alloc_id), offset) => {
149 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
150 ConstValue::ByRef { alloc, offset }
153 assert!(mplace.layout.is_zst());
155 offset.bytes() % mplace.layout.align.abi.bytes(),
157 "this MPlaceTy must come from a validated constant, thus we can assume the \
158 alignment is correct",
160 ConstValue::ZeroSized
165 Ok(ref mplace) => to_const_value(mplace),
166 // see comment on `let try_as_immediate` above
167 Err(imm) => match *imm {
168 _ if imm.layout.is_zst() => ConstValue::ZeroSized,
169 Immediate::Scalar(x) => match x {
170 ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s),
171 ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()),
173 Immediate::ScalarPair(a, b) => {
174 debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
175 // We know `offset` is relative to the allocation, so we can use `into_parts`.
176 let (data, start) = match a.to_pointer(ecx).unwrap().into_parts() {
177 (Some(alloc_id), offset) => {
178 (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes())
181 ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
187 let len = b.to_machine_usize(ecx).unwrap();
188 let start = start.try_into().unwrap();
189 let len: usize = len.try_into().unwrap();
190 ConstValue::Slice { data, start, end: start + len }
192 Immediate::Uninit => to_const_value(&op.assert_mem_place()),
197 #[instrument(skip(tcx), level = "debug")]
198 pub(crate) fn turn_into_const_value<'tcx>(
200 constant: ConstAlloc<'tcx>,
201 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
202 ) -> ConstValue<'tcx> {
204 let def_id = cid.instance.def.def_id();
205 let is_static = tcx.is_static(def_id);
206 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
208 let mplace = ecx.raw_const_to_mplace(constant).expect(
209 "can only fail if layout computation failed, \
210 which should have given a good error before ever invoking this function",
213 !is_static || cid.promoted.is_some(),
214 "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead"
217 // Turn this into a proper constant.
218 let const_val = op_to_const(&ecx, &mplace.into());
224 #[instrument(skip(tcx), level = "debug")]
225 pub fn eval_to_const_value_raw_provider<'tcx>(
227 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
228 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
229 assert!(key.param_env.is_const());
230 // see comment in eval_to_allocation_raw_provider for what we're doing here
231 if key.param_env.reveal() == Reveal::All {
233 key.param_env = key.param_env.with_user_facing();
234 match tcx.eval_to_const_value_raw(key) {
235 // try again with reveal all as requested
236 Err(ErrorHandled::TooGeneric) => {}
238 other => return other,
242 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
243 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
244 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
245 let ty = key.value.instance.ty(tcx, key.param_env);
246 let ty::FnDef(_, substs) = ty.kind() else {
247 bug!("intrinsic with type {:?}", ty);
249 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
250 let span = tcx.def_span(def_id);
251 let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
252 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
256 tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
259 #[instrument(skip(tcx), level = "debug")]
260 pub fn eval_to_allocation_raw_provider<'tcx>(
262 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
263 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
264 assert!(key.param_env.is_const());
265 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
266 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
267 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
268 // computed. For a large percentage of constants that will already have succeeded. Only
269 // associated constants of generic functions will fail due to not enough monomorphization
270 // information being available.
272 // In case we fail in the `UserFacing` variant, we just do the real computation.
273 if key.param_env.reveal() == Reveal::All {
275 key.param_env = key.param_env.with_user_facing();
276 match tcx.eval_to_allocation_raw(key) {
277 // try again with reveal all as requested
278 Err(ErrorHandled::TooGeneric) => {}
280 other => return other,
283 if cfg!(debug_assertions) {
284 // Make sure we format the instance even if we do not print it.
285 // This serves as a regression test against an ICE on printing.
286 // The next two lines concatenated contain some discussion:
287 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
288 // subject/anon_const_instance_printing/near/135980032
289 let instance = with_no_trimmed_paths!(key.value.instance.to_string());
290 trace!("const eval: {:?} ({})", key, instance);
294 let def = cid.instance.def.with_opt_param();
295 let is_static = tcx.is_static(def.did);
297 let mut ecx = InterpCx::new(
299 tcx.def_span(def.did),
301 // Statics (and promoteds inside statics) may access other statics, because unlike consts
302 // they do not have to behave "as if" they were evaluated at runtime.
303 CompileTimeInterpreter::new(tcx.const_eval_limit(), /*can_access_statics:*/ is_static),
306 let res = ecx.load_mir(cid.instance.def, cid.promoted);
307 match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
309 let err = ConstEvalErr::new(&ecx, error, None);
310 // Some CTFE errors raise just a lint, not a hard error; see
311 // <https://github.com/rust-lang/rust/issues/71800>.
312 let is_hard_err = if let Some(def) = def.as_local() {
313 // (Associated) consts only emit a lint, since they might be unused.
314 !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
315 // check if the inner InterpError is hard
316 || err.error.is_hard_err()
318 // use of broken constant from other crate: always an error
323 let msg = if is_static {
324 Cow::from("could not evaluate static initializer")
326 // If the current item has generics, we'd like to enrich the message with the
327 // instance and its substs: to show the actual compile-time values, in addition to
328 // the expression, leading to the const eval error.
329 let instance = &key.value.instance;
330 if !instance.substs.is_empty() {
331 let instance = with_no_trimmed_paths!(instance.to_string());
332 let msg = format!("evaluation of `{}` failed", instance);
335 Cow::from("evaluation of constant value failed")
339 Err(err.report_as_error(ecx.tcx.at(err.span), &msg))
341 let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
342 Err(err.report_as_lint(
343 tcx.at(tcx.def_span(def.did)),
344 "any use of this value will cause an error",
351 // Since evaluation had no errors, validate the resulting constant.
352 // This is a separate `try` block to provide more targeted error reporting.
353 let validation = try {
354 let mut ref_tracking = RefTracking::new(mplace);
355 let mut inner = false;
356 while let Some((mplace, path)) = ref_tracking.todo.pop() {
357 let mode = match tcx.static_mutability(cid.instance.def_id()) {
358 Some(_) if cid.promoted.is_some() => {
359 // Promoteds in statics are allowed to point to statics.
360 CtfeValidationMode::Const { inner, allow_static_ptrs: true }
362 Some(_) => CtfeValidationMode::Regular, // a `static`
363 None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
365 ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
369 let alloc_id = mplace.ptr.provenance.unwrap();
370 if let Err(error) = validation {
371 // Validation failed, report an error. This is always a hard error.
372 let err = ConstEvalErr::new(&ecx, error, None);
373 Err(err.struct_error(
375 "it is undefined behavior to use this value",
377 diag.note(NOTE_ON_UNDEFINED_BEHAVIOR_ERROR);
379 "the raw bytes of the constant ({}",
382 ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner()
388 // Convert to raw constant
389 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })