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, InterpError, InterpResult, MPlaceTy, MemoryKind, OpTy,
6 RefTracking, 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, 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 ecx.machine.check_alignment = false; // interning doesn't need to respect alignment
78 intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
79 // we leave alignment checks off, since this `ecx` will not be used for further evaluation anyway
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. It never performs alignment checks.
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(
104 tcx.const_eval_limit(),
106 /*check_alignment:*/ false,
111 /// This function converts an interpreter value into a constant that is meant for use in the
113 #[instrument(skip(ecx), level = "debug")]
114 pub(super) fn op_to_const<'tcx>(
115 ecx: &CompileTimeEvalContext<'_, 'tcx>,
117 ) -> ConstValue<'tcx> {
118 // We do not have value optimizations for everything.
119 // Only scalars and slices, since they are very common.
120 // Note that further down we turn scalars of uninitialized bits back to `ByRef`. These can result
121 // from scalar unions that are initialized with one of their zero sized variants. We could
122 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUninit`, but that would affect all
123 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
124 // `Undef` situation.
125 let try_as_immediate = match op.layout.abi {
126 Abi::Scalar(abi::Scalar::Initialized { .. }) => true,
127 Abi::ScalarPair(..) => match op.layout.ty.kind() {
128 ty::Ref(_, inner, _) => match *inner.kind() {
129 ty::Slice(elem) => elem == ecx.tcx.types.u8,
137 let immediate = if try_as_immediate {
138 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
140 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
141 // When we come back from raw const eval, we are always by-ref. The only way our op here is
142 // by-val is if we are in destructure_mir_constant, i.e., if this is (a field of) something that we
143 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
144 // structs containing such.
150 // We know `offset` is relative to the allocation, so we can use `into_parts`.
151 let to_const_value = |mplace: &MPlaceTy<'_>| {
152 debug!("to_const_value(mplace: {:?})", mplace);
153 match mplace.ptr.into_parts() {
154 (Some(alloc_id), offset) => {
155 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
156 ConstValue::ByRef { alloc, offset }
159 assert!(mplace.layout.is_zst());
161 offset.bytes() % mplace.layout.align.abi.bytes(),
163 "this MPlaceTy must come from a validated constant, thus we can assume the \
164 alignment is correct",
166 ConstValue::ZeroSized
171 Ok(ref mplace) => to_const_value(mplace),
172 // see comment on `let try_as_immediate` above
173 Err(imm) => match *imm {
174 _ if imm.layout.is_zst() => ConstValue::ZeroSized,
175 Immediate::Scalar(x) => ConstValue::Scalar(x),
176 Immediate::ScalarPair(a, b) => {
177 debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
178 // We know `offset` is relative to the allocation, so we can use `into_parts`.
179 let (data, start) = match a.to_pointer(ecx).unwrap().into_parts() {
180 (Some(alloc_id), offset) => {
181 (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes())
184 ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
190 let len = b.to_machine_usize(ecx).unwrap();
191 let start = start.try_into().unwrap();
192 let len: usize = len.try_into().unwrap();
193 ConstValue::Slice { data, start, end: start + len }
195 Immediate::Uninit => to_const_value(&op.assert_mem_place()),
200 #[instrument(skip(tcx), level = "debug", ret)]
201 pub(crate) fn turn_into_const_value<'tcx>(
203 constant: ConstAlloc<'tcx>,
204 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
205 ) -> ConstValue<'tcx> {
207 let def_id = cid.instance.def.def_id();
208 let is_static = tcx.is_static(def_id);
209 // This is just accessing an already computed constant, so no need to check alginment here.
210 let ecx = mk_eval_cx(
212 tcx.def_span(key.value.instance.def_id()),
214 /*can_access_statics:*/ is_static,
217 let mplace = ecx.raw_const_to_mplace(constant).expect(
218 "can only fail if layout computation failed, \
219 which should have given a good error before ever invoking this function",
222 !is_static || cid.promoted.is_some(),
223 "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead"
226 // Turn this into a proper constant.
227 op_to_const(&ecx, &mplace.into())
230 #[instrument(skip(tcx), level = "debug")]
231 pub fn eval_to_const_value_raw_provider<'tcx>(
233 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
234 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
235 assert!(key.param_env.is_const());
236 // see comment in eval_to_allocation_raw_provider for what we're doing here
237 if key.param_env.reveal() == Reveal::All {
239 key.param_env = key.param_env.with_user_facing();
240 match tcx.eval_to_const_value_raw(key) {
241 // try again with reveal all as requested
242 Err(ErrorHandled::TooGeneric) => {}
244 other => return other,
248 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
249 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
250 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
251 let ty = key.value.instance.ty(tcx, key.param_env);
252 let ty::FnDef(_, substs) = ty.kind() else {
253 bug!("intrinsic with type {:?}", ty);
255 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
256 let span = tcx.def_span(def_id);
257 let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
258 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
262 tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
265 #[instrument(skip(tcx), level = "debug")]
266 pub fn eval_to_allocation_raw_provider<'tcx>(
268 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
269 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
270 assert!(key.param_env.is_const());
271 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
272 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
273 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
274 // computed. For a large percentage of constants that will already have succeeded. Only
275 // associated constants of generic functions will fail due to not enough monomorphization
276 // information being available.
278 // In case we fail in the `UserFacing` variant, we just do the real computation.
279 if key.param_env.reveal() == Reveal::All {
281 key.param_env = key.param_env.with_user_facing();
282 match tcx.eval_to_allocation_raw(key) {
283 // try again with reveal all as requested
284 Err(ErrorHandled::TooGeneric) => {}
286 other => return other,
289 if cfg!(debug_assertions) {
290 // Make sure we format the instance even if we do not print it.
291 // This serves as a regression test against an ICE on printing.
292 // The next two lines concatenated contain some discussion:
293 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
294 // subject/anon_const_instance_printing/near/135980032
295 let instance = with_no_trimmed_paths!(key.value.instance.to_string());
296 trace!("const eval: {:?} ({})", key, instance);
300 let def = cid.instance.def.with_opt_param();
301 let is_static = tcx.is_static(def.did);
303 let mut ecx = InterpCx::new(
305 tcx.def_span(def.did),
307 // Statics (and promoteds inside statics) may access other statics, because unlike consts
308 // they do not have to behave "as if" they were evaluated at runtime.
309 CompileTimeInterpreter::new(
310 tcx.const_eval_limit(),
311 /*can_access_statics:*/ is_static,
312 /*check_alignment:*/ tcx.sess.opts.unstable_opts.extra_const_ub_checks,
316 let res = ecx.load_mir(cid.instance.def, cid.promoted);
317 match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
319 let err = ConstEvalErr::new(&ecx, error, None);
320 let msg = if is_static {
321 Cow::from("could not evaluate static initializer")
323 // If the current item has generics, we'd like to enrich the message with the
324 // instance and its substs: to show the actual compile-time values, in addition to
325 // the expression, leading to the const eval error.
326 let instance = &key.value.instance;
327 if !instance.substs.is_empty() {
328 let instance = with_no_trimmed_paths!(instance.to_string());
329 let msg = format!("evaluation of `{}` failed", instance);
332 Cow::from("evaluation of constant value failed")
336 Err(err.report_as_error(ecx.tcx.at(err.span), &msg))
339 // Since evaluation had no errors, validate the resulting constant.
340 // This is a separate `try` block to provide more targeted error reporting.
341 let validation = try {
342 let mut ref_tracking = RefTracking::new(mplace);
343 let mut inner = false;
344 while let Some((mplace, path)) = ref_tracking.todo.pop() {
345 let mode = match tcx.static_mutability(cid.instance.def_id()) {
346 Some(_) if cid.promoted.is_some() => {
347 // Promoteds in statics are allowed to point to statics.
348 CtfeValidationMode::Const { inner, allow_static_ptrs: true }
350 Some(_) => CtfeValidationMode::Regular, // a `static`
351 None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
353 ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
357 let alloc_id = mplace.ptr.provenance.unwrap();
358 if let Err(error) = validation {
359 // Validation failed, report an error. This is always a hard error.
360 let err = ConstEvalErr::new(&ecx, error, None);
361 Err(err.struct_error(
363 "it is undefined behavior to use this value",
365 if matches!(err.error, InterpError::UndefinedBehavior(_)) {
366 diag.note(NOTE_ON_UNDEFINED_BEHAVIOR_ERROR);
369 "the raw bytes of the constant ({}",
372 ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner()
378 // Convert to raw constant
379 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })