1 use super::{error_to_const_error, CompileTimeEvalContext, CompileTimeInterpreter, MemoryExtra};
2 use crate::interpret::eval_nullary_intrinsic;
3 use crate::interpret::{
4 intern_const_alloc_recursive, Allocation, ConstValue, GlobalId, Immediate, InternKind,
5 InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RawConst, RefTracking, Scalar,
6 ScalarMaybeUninit, StackPopCleanup,
8 use rustc_hir::def::DefKind;
10 use rustc_middle::mir::interpret::{ConstEvalErr, ErrorHandled};
11 use rustc_middle::traits::Reveal;
12 use rustc_middle::ty::{self, subst::Subst, TyCtxt};
13 use rustc_span::source_map::Span;
14 use rustc_target::abi::{Abi, LayoutOf};
15 use std::convert::TryInto;
17 pub fn note_on_undefined_behavior_error() -> &'static str {
18 "The rules on what exactly is undefined behavior aren't clear, \
19 so this check might be overzealous. Please open an issue on the rustc \
20 repository if you believe it should not be considered undefined behavior."
23 // Returns a pointer to where the result lives
24 fn eval_body_using_ecx<'mir, 'tcx>(
25 ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
27 body: &'mir mir::Body<'tcx>,
28 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
29 debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
31 let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
32 assert!(!layout.is_unsized());
33 let ret = ecx.allocate(layout, MemoryKind::Stack);
35 let name = ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()));
36 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
37 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
39 // Assert all args (if any) are zero-sized types; `eval_body_using_ecx` doesn't
40 // make sense if the body is expecting nontrivial arguments.
41 // (The alternative would be to use `eval_fn_call` with an args slice.)
42 for arg in body.args_iter() {
43 let decl = body.local_decls.get(arg).expect("arg missing from local_decls");
44 let layout = ecx.layout_of(decl.ty.subst(tcx, cid.instance.substs))?;
45 assert!(layout.is_zst())
52 StackPopCleanup::None { cleanup: false },
55 // The main interpreter loop.
59 let intern_kind = match tcx.static_mutability(cid.instance.def_id()) {
60 Some(m) => InternKind::Static(m),
61 None if cid.promoted.is_some() => InternKind::Promoted,
62 _ => InternKind::Constant,
64 intern_const_alloc_recursive(
68 body.ignore_interior_mut_in_const_validation,
71 debug!("eval_body_using_ecx done: {:?}", *ret);
75 /// The `InterpCx` is only meant to be used to do field and index projections into constants for
76 /// `simd_shuffle` and const patterns in match arms.
78 /// The function containing the `match` that is currently being analyzed may have generic bounds
79 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
80 /// of a function's generic parameter will require knowledge about the bounds on the generic
81 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
82 pub(super) fn mk_eval_cx<'mir, 'tcx>(
85 param_env: ty::ParamEnv<'tcx>,
86 can_access_statics: bool,
87 ) -> CompileTimeEvalContext<'mir, 'tcx> {
88 debug!("mk_eval_cx: {:?}", param_env);
93 CompileTimeInterpreter::new(tcx.sess.const_eval_limit()),
94 MemoryExtra { can_access_statics },
98 pub(super) fn op_to_const<'tcx>(
99 ecx: &CompileTimeEvalContext<'_, 'tcx>,
101 ) -> ConstValue<'tcx> {
102 // We do not have value optimizations for everything.
103 // Only scalars and slices, since they are very common.
104 // Note that further down we turn scalars of uninitialized bits back to `ByRef`. These can result
105 // from scalar unions that are initialized with one of their zero sized variants. We could
106 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUninit`, but that would affect all
107 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
108 // `Undef` situation.
109 let try_as_immediate = match op.layout.abi {
110 Abi::Scalar(..) => true,
111 Abi::ScalarPair(..) => match op.layout.ty.kind {
112 ty::Ref(_, inner, _) => match inner.kind {
113 ty::Slice(elem) => elem == ecx.tcx.types.u8,
121 let immediate = if try_as_immediate {
122 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
124 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
125 // When we come back from raw const eval, we are always by-ref. The only way our op here is
126 // by-val is if we are in destructure_const, i.e., if this is (a field of) something that we
127 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
128 // structs containing such.
129 op.try_as_mplace(ecx)
132 let to_const_value = |mplace: MPlaceTy<'_>| match mplace.ptr {
133 Scalar::Ptr(ptr) => {
134 let alloc = ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory();
135 ConstValue::ByRef { alloc, offset: ptr.offset }
137 Scalar::Raw { data, .. } => {
138 assert!(mplace.layout.is_zst());
141 mplace.layout.align.abi.bytes().into(),
142 "this MPlaceTy must come from `try_as_mplace` being used on a zst, so we know what
143 value this integer address must have",
145 ConstValue::Scalar(Scalar::zst())
149 Ok(mplace) => to_const_value(mplace),
150 // see comment on `let try_as_immediate` above
151 Err(imm) => match *imm {
152 Immediate::Scalar(x) => match x {
153 ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s),
154 ScalarMaybeUninit::Uninit => to_const_value(op.assert_mem_place(ecx)),
156 Immediate::ScalarPair(a, b) => {
157 let (data, start) = match a.check_init().unwrap() {
158 Scalar::Ptr(ptr) => {
159 (ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory(), ptr.offset.bytes())
161 Scalar::Raw { .. } => (
163 .intern_const_alloc(Allocation::from_byte_aligned_bytes(b"" as &[u8])),
167 let len = b.to_machine_usize(ecx).unwrap();
168 let start = start.try_into().unwrap();
169 let len: usize = len.try_into().unwrap();
170 ConstValue::Slice { data, start, end: start + len }
176 fn validate_and_turn_into_const<'tcx>(
178 constant: RawConst<'tcx>,
179 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
180 ) -> ::rustc_middle::mir::interpret::ConstEvalResult<'tcx> {
182 let def_id = cid.instance.def.def_id();
183 let is_static = tcx.is_static(def_id);
184 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
186 let mplace = ecx.raw_const_to_mplace(constant)?;
188 // FIXME do not validate promoteds until a decision on
189 // https://github.com/rust-lang/rust/issues/67465 is made
190 if cid.promoted.is_none() {
191 let mut ref_tracking = RefTracking::new(mplace);
192 while let Some((mplace, path)) = ref_tracking.todo.pop() {
193 ecx.const_validate_operand(
197 /*may_ref_to_static*/ ecx.memory.extra.can_access_statics,
201 // Now that we validated, turn this into a proper constant.
202 // Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
203 // whether they become immediates.
204 if is_static || cid.promoted.is_some() {
205 let ptr = mplace.ptr.assert_ptr();
206 Ok(ConstValue::ByRef {
207 alloc: ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory(),
211 Ok(op_to_const(&ecx, mplace.into()))
215 val.map_err(|error| {
216 let err = error_to_const_error(&ecx, error, None);
217 err.struct_error(ecx.tcx, "it is undefined behavior to use this value", |mut diag| {
218 diag.note(note_on_undefined_behavior_error());
224 pub fn const_eval_validated_provider<'tcx>(
226 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
227 ) -> ::rustc_middle::mir::interpret::ConstEvalResult<'tcx> {
228 // see comment in const_eval_raw_provider for what we're doing here
229 if key.param_env.reveal() == Reveal::All {
231 key.param_env = key.param_env.with_user_facing();
232 match tcx.const_eval_validated(key) {
233 // try again with reveal all as requested
234 Err(ErrorHandled::TooGeneric) => {}
236 other => return other,
240 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
241 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
242 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
243 let ty = key.value.instance.ty(tcx, key.param_env);
244 let substs = match ty.kind {
245 ty::FnDef(_, substs) => substs,
246 _ => bug!("intrinsic with type {:?}", ty),
248 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
249 let span = tcx.def_span(def_id);
250 let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
251 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
255 tcx.const_eval_raw(key).and_then(|val| validate_and_turn_into_const(tcx, val, key))
258 pub fn const_eval_raw_provider<'tcx>(
260 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
261 ) -> ::rustc_middle::mir::interpret::ConstEvalRawResult<'tcx> {
262 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
263 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
264 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
265 // computed. For a large percentage of constants that will already have succeeded. Only
266 // associated constants of generic functions will fail due to not enough monomorphization
267 // information being available.
269 // In case we fail in the `UserFacing` variant, we just do the real computation.
270 if key.param_env.reveal() == Reveal::All {
272 key.param_env = key.param_env.with_user_facing();
273 match tcx.const_eval_raw(key) {
274 // try again with reveal all as requested
275 Err(ErrorHandled::TooGeneric) => {}
277 other => return other,
280 if cfg!(debug_assertions) {
281 // Make sure we format the instance even if we do not print it.
282 // This serves as a regression test against an ICE on printing.
283 // The next two lines concatenated contain some discussion:
284 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
285 // subject/anon_const_instance_printing/near/135980032
286 let instance = key.value.instance.to_string();
287 trace!("const eval: {:?} ({})", key, instance);
291 let def = cid.instance.def.with_opt_param();
293 if let Some(def) = def.as_local() {
294 if tcx.has_typeck_results(def.did) {
295 if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
296 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.sess.const_eval_limit()),
308 MemoryExtra { can_access_statics: is_static },
311 let res = ecx.load_mir(cid.instance.def, cid.promoted);
312 res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body))
313 .map(|place| RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
315 let err = error_to_const_error(&ecx, error, None);
316 // errors in statics are always emitted as fatal errors
318 // Ensure that if the above error was either `TooGeneric` or `Reported`
319 // an error must be reported.
320 let v = err.report_as_error(
321 ecx.tcx.at(ecx.cur_span()),
322 "could not evaluate static initializer",
325 // If this is `Reveal:All`, then we need to make sure an error is reported but if
326 // this is `Reveal::UserFacing`, then it's expected that we could get a
327 // `TooGeneric` error. When we fall back to `Reveal::All`, then it will either
328 // succeed or we'll report this error then.
329 if key.param_env.reveal() == Reveal::All {
330 tcx.sess.delay_span_bug(
332 &format!("static eval failure did not emit an error: {:#?}", v),
337 } else if let Some(def) = def.as_local() {
338 // constant defined in this crate, we can figure out a lint level!
339 match tcx.def_kind(def.did.to_def_id()) {
340 // constants never produce a hard error at the definition site. Anything else is
341 // a backwards compatibility hazard (and will break old versions of winapi for
344 // note that validation may still cause a hard error on this very same constant,
345 // because any code that existed before validation could not have failed
346 // validation thus preventing such a hard error from being a backwards
347 // compatibility hazard
348 DefKind::Const | DefKind::AssocConst => {
349 let hir_id = tcx.hir().as_local_hir_id(def.did);
351 tcx.at(tcx.def_span(def.did)),
352 "any use of this value will cause an error",
357 // promoting runtime code is only allowed to error if it references broken
358 // constants any other kind of error will be reported to the user as a
359 // deny-by-default lint
361 if let Some(p) = cid.promoted {
362 let span = tcx.promoted_mir_of_opt_const_arg(def.to_global())[p].span;
363 if let err_inval!(ReferencedConstant) = err.error {
366 "evaluation of constant expression failed",
371 "reaching this expression at runtime will panic or abort",
372 tcx.hir().as_local_hir_id(def.did),
376 // anything else (array lengths, enum initializers, constant patterns) are
377 // reported as hard errors
380 ecx.tcx.at(ecx.cur_span()),
381 "evaluation of constant value failed",
387 // use of broken constant from other crate
388 err.report_as_error(ecx.tcx.at(ecx.cur_span()), "could not evaluate constant")