1 use crate::const_eval::CheckAlignment;
4 use either::{Left, Right};
6 use rustc_hir::def::DefKind;
8 use rustc_middle::mir::interpret::ErrorHandled;
9 use rustc_middle::mir::pretty::display_allocation;
10 use rustc_middle::traits::Reveal;
11 use rustc_middle::ty::layout::LayoutOf;
12 use rustc_middle::ty::print::with_no_trimmed_paths;
13 use rustc_middle::ty::{self, TyCtxt};
14 use rustc_span::source_map::Span;
15 use rustc_target::abi::{self, Abi};
17 use super::{CompileTimeEvalContext, CompileTimeInterpreter, ConstEvalErr};
18 use crate::interpret::eval_nullary_intrinsic;
19 use crate::interpret::{
20 intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, CtfeValidationMode, GlobalId,
21 Immediate, InternKind, InterpCx, InterpError, InterpResult, MPlaceTy, MemoryKind, OpTy,
22 RefTracking, StackPopCleanup,
25 const NOTE_ON_UNDEFINED_BEHAVIOR_ERROR: &str = "The rules on what exactly is undefined behavior aren't clear, \
26 so this check might be overzealous. Please open an issue on the rustc \
27 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.bound_return_ty().subst(tcx, cid.instance.substs))?;
52 assert!(layout.is_sized());
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::Root { 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 ecx.machine.check_alignment = CheckAlignment::No; // interning doesn't need to respect alignment
81 intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
82 // we leave alignment checks off, since this `ecx` will not be used for further evaluation anyway
84 debug!("eval_body_using_ecx done: {:?}", *ret);
88 /// The `InterpCx` is only meant to be used to do field and index projections into constants for
89 /// `simd_shuffle` and const patterns in match arms. It never performs alignment checks.
91 /// The function containing the `match` that is currently being analyzed may have generic bounds
92 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
93 /// of a function's generic parameter will require knowledge about the bounds on the generic
94 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
95 pub(super) fn mk_eval_cx<'mir, 'tcx>(
98 param_env: ty::ParamEnv<'tcx>,
99 can_access_statics: bool,
100 ) -> CompileTimeEvalContext<'mir, 'tcx> {
101 debug!("mk_eval_cx: {:?}", param_env);
106 CompileTimeInterpreter::new(tcx.const_eval_limit(), can_access_statics, CheckAlignment::No),
110 /// This function converts an interpreter value into a constant that is meant for use in the
112 #[instrument(skip(ecx), level = "debug")]
113 pub(super) fn op_to_const<'tcx>(
114 ecx: &CompileTimeEvalContext<'_, 'tcx>,
116 ) -> ConstValue<'tcx> {
117 // We do not have value optimizations for everything.
118 // Only scalars and slices, since they are very common.
119 // Note that further down we turn scalars of uninitialized bits back to `ByRef`. These can result
120 // from scalar unions that are initialized with one of their zero sized variants. We could
121 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUninit`, but that would affect all
122 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
123 // `Undef` situation.
124 let try_as_immediate = match op.layout.abi {
125 Abi::Scalar(abi::Scalar::Initialized { .. }) => true,
126 Abi::ScalarPair(..) => match op.layout.ty.kind() {
127 ty::Ref(_, inner, _) => match *inner.kind() {
128 ty::Slice(elem) => elem == ecx.tcx.types.u8,
136 let immediate = if try_as_immediate {
137 Right(ecx.read_immediate(op).expect("normalization works on validated constants"))
139 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
140 // When we come back from raw const eval, we are always by-ref. The only way our op here is
141 // by-val is if we are in destructure_mir_constant, i.e., if this is (a field of) something that we
142 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
143 // structs containing such.
144 op.as_mplace_or_imm()
149 // We know `offset` is relative to the allocation, so we can use `into_parts`.
150 let to_const_value = |mplace: &MPlaceTy<'_>| {
151 debug!("to_const_value(mplace: {:?})", mplace);
152 match mplace.ptr.into_parts() {
153 (Some(alloc_id), offset) => {
154 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
155 ConstValue::ByRef { alloc, offset }
158 assert!(mplace.layout.is_zst());
160 offset.bytes() % mplace.layout.align.abi.bytes(),
162 "this MPlaceTy must come from a validated constant, thus we can assume the \
163 alignment is correct",
165 ConstValue::ZeroSized
170 Left(ref mplace) => to_const_value(mplace),
171 // see comment on `let try_as_immediate` above
172 Right(imm) => match *imm {
173 _ if imm.layout.is_zst() => ConstValue::ZeroSized,
174 Immediate::Scalar(x) => ConstValue::Scalar(x),
175 Immediate::ScalarPair(a, b) => {
176 debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
177 // We know `offset` is relative to the allocation, so we can use `into_parts`.
178 let (data, start) = match a.to_pointer(ecx).unwrap().into_parts() {
179 (Some(alloc_id), offset) => {
180 (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes())
183 ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
189 let len = b.to_machine_usize(ecx).unwrap();
190 let start = start.try_into().unwrap();
191 let len: usize = len.try_into().unwrap();
192 ConstValue::Slice { data, start, end: start + len }
194 Immediate::Uninit => to_const_value(&op.assert_mem_place()),
199 #[instrument(skip(tcx), level = "debug", ret)]
200 pub(crate) fn turn_into_const_value<'tcx>(
202 constant: ConstAlloc<'tcx>,
203 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
204 ) -> ConstValue<'tcx> {
206 let def_id = cid.instance.def.def_id();
207 let is_static = tcx.is_static(def_id);
208 // This is just accessing an already computed constant, so no need to check alginment here.
209 let ecx = mk_eval_cx(
211 tcx.def_span(key.value.instance.def_id()),
213 /*can_access_statics:*/ is_static,
216 let mplace = ecx.raw_const_to_mplace(constant).expect(
217 "can only fail if layout computation failed, \
218 which should have given a good error before ever invoking this function",
221 !is_static || cid.promoted.is_some(),
222 "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead"
225 // Turn this into a proper constant.
226 op_to_const(&ecx, &mplace.into())
229 #[instrument(skip(tcx), level = "debug")]
230 pub fn eval_to_const_value_raw_provider<'tcx>(
232 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
233 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
234 assert!(key.param_env.is_const());
235 // see comment in eval_to_allocation_raw_provider for what we're doing here
236 if key.param_env.reveal() == Reveal::All {
238 key.param_env = key.param_env.with_user_facing();
239 match tcx.eval_to_const_value_raw(key) {
240 // try again with reveal all as requested
241 Err(ErrorHandled::TooGeneric) => {}
243 other => return other,
247 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
248 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
249 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
250 let ty = key.value.instance.ty(tcx, key.param_env);
251 let ty::FnDef(_, substs) = ty.kind() else {
252 bug!("intrinsic with type {:?}", ty);
254 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
255 let span = tcx.def_span(def_id);
256 let error = ConstEvalErr { error: error.into_kind(), stacktrace: vec![], span };
257 error.report(tcx.at(span), "could not evaluate nullary intrinsic")
261 tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
264 #[instrument(skip(tcx), level = "debug")]
265 pub fn eval_to_allocation_raw_provider<'tcx>(
267 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
268 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
269 assert!(key.param_env.is_const());
270 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
271 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
272 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
273 // computed. For a large percentage of constants that will already have succeeded. Only
274 // associated constants of generic functions will fail due to not enough monomorphization
275 // information being available.
277 // In case we fail in the `UserFacing` variant, we just do the real computation.
278 if key.param_env.reveal() == Reveal::All {
280 key.param_env = key.param_env.with_user_facing();
281 match tcx.eval_to_allocation_raw(key) {
282 // try again with reveal all as requested
283 Err(ErrorHandled::TooGeneric) => {}
285 other => return other,
288 if cfg!(debug_assertions) {
289 // Make sure we format the instance even if we do not print it.
290 // This serves as a regression test against an ICE on printing.
291 // The next two lines concatenated contain some discussion:
292 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
293 // subject/anon_const_instance_printing/near/135980032
294 let instance = with_no_trimmed_paths!(key.value.instance.to_string());
295 trace!("const eval: {:?} ({})", key, instance);
299 let def = cid.instance.def.with_opt_param();
300 let is_static = tcx.is_static(def.did);
302 let mut ecx = InterpCx::new(
304 tcx.def_span(def.did),
306 // Statics (and promoteds inside statics) may access other statics, because unlike consts
307 // they do not have to behave "as if" they were evaluated at runtime.
308 CompileTimeInterpreter::new(
309 tcx.const_eval_limit(),
310 /*can_access_statics:*/ is_static,
311 if tcx.sess.opts.unstable_opts.extra_const_ub_checks {
312 CheckAlignment::Error
314 CheckAlignment::FutureIncompat
319 let res = ecx.load_mir(cid.instance.def, cid.promoted);
320 match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
322 let err = ConstEvalErr::new(&ecx, error, None);
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(ecx.tcx.at(err.span), &msg))
342 // Since evaluation had no errors, validate the resulting constant.
343 // This is a separate `try` block to provide more targeted error reporting.
344 let validation = try {
345 let mut ref_tracking = RefTracking::new(mplace);
346 let mut inner = false;
347 while let Some((mplace, path)) = ref_tracking.todo.pop() {
348 let mode = match tcx.static_mutability(cid.instance.def_id()) {
349 Some(_) if cid.promoted.is_some() => {
350 // Promoteds in statics are allowed to point to statics.
351 CtfeValidationMode::Const { inner, allow_static_ptrs: true }
353 Some(_) => CtfeValidationMode::Regular, // a `static`
354 None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
356 ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
360 let alloc_id = mplace.ptr.provenance.unwrap();
361 if let Err(error) = validation {
362 // Validation failed, report an error. This is always a hard error.
363 let err = ConstEvalErr::new(&ecx, error, None);
364 Err(err.report_decorated(
366 "it is undefined behavior to use this value",
368 if matches!(err.error, InterpError::UndefinedBehavior(_)) {
369 diag.note(NOTE_ON_UNDEFINED_BEHAVIOR_ERROR);
372 "the raw bytes of the constant ({}",
375 ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner()
381 // Convert to raw constant
382 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })