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Move const eval query components into their own module

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This commit is contained in:
Oliver Scherer 2019-12-25 01:06:51 +01:00
parent 3e7fa3c6f2
commit 2d67edd32c
3 changed files with 234 additions and 228 deletions
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230
src/librustc_mir/const_eval.rs
View File

@ -5,12 +5,8 @@ use std::error::Error;
use std::fmt;
use std::hash::Hash;
use crate::interpret::eval_nullary_intrinsic;
use crate::interpret::eval_nullary_intrinsic;
use rustc::hir::def::DefKind;
use rustc::mir;
use rustc::mir::interpret::{ConstEvalErr, ErrorHandled, ScalarMaybeUndef};
use rustc::traits::Reveal;
use rustc::mir::interpret::ScalarMaybeUndef;
use rustc::ty::layout::{self, LayoutOf, VariantIdx};
use rustc::ty::{self, subst::Subst, TyCtxt};
@ -21,15 +17,14 @@ use syntax::{
use crate::interpret::{
intern_const_alloc_recursive, Allocation, ConstValue, GlobalId, ImmTy, Immediate, InterpCx,
InterpErrorInfo, InterpResult, MPlaceTy, Machine, MemoryKind, OpTy, RawConst, RefTracking,
Scalar, StackPopCleanup,
InterpResult, MPlaceTy, MemoryKind, OpTy, Scalar, StackPopCleanup,
};
mod error;
mod machine;
mod query;
pub use error::*;
pub use machine::*;
pub use query::*;
/// The `InterpCx` is only meant to be used to do field and index projections into constants for
/// `simd_shuffle` and const patterns in match arms.
@ -225,220 +220,3 @@ pub fn const_variant_index<'tcx>(
let op = ecx.eval_const_to_op(val, None).unwrap();
ecx.read_discriminant(op).unwrap().1
}
/// Turn an interpreter error into something to report to the user.
/// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
/// Should be called only if the error is actually going to to be reported!
pub fn error_to_const_error<'mir, 'tcx, M: Machine<'mir, 'tcx>>(
ecx: &InterpCx<'mir, 'tcx, M>,
mut error: InterpErrorInfo<'tcx>,
) -> ConstEvalErr<'tcx> {
error.print_backtrace();
let stacktrace = ecx.generate_stacktrace(None);
ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
}
pub fn note_on_undefined_behavior_error() -> &'static str {
"The rules on what exactly is undefined behavior aren't clear, \
so this check might be overzealous. Please open an issue on the rustc \
repository if you believe it should not be considered undefined behavior."
}
fn validate_and_turn_into_const<'tcx>(
tcx: TyCtxt<'tcx>,
constant: RawConst<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
let cid = key.value;
let def_id = cid.instance.def.def_id();
let is_static = tcx.is_static(def_id);
let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
let val = (|| {
let mplace = ecx.raw_const_to_mplace(constant)?;
let mut ref_tracking = RefTracking::new(mplace);
while let Some((mplace, path)) = ref_tracking.todo.pop() {
ecx.validate_operand(mplace.into(), path, Some(&mut ref_tracking))?;
}
// Now that we validated, turn this into a proper constant.
// Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
// whether they become immediates.
if is_static || cid.promoted.is_some() {
let ptr = mplace.ptr.to_ptr()?;
Ok(tcx.mk_const(ty::Const {
val: ty::ConstKind::Value(ConstValue::ByRef {
alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
offset: ptr.offset,
}),
ty: mplace.layout.ty,
}))
} else {
Ok(op_to_const(&ecx, mplace.into()))
}
})();
val.map_err(|error| {
let err = error_to_const_error(&ecx, error);
match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
Ok(mut diag) => {
diag.note(note_on_undefined_behavior_error());
diag.emit();
ErrorHandled::Reported
}
Err(err) => err,
}
})
}
pub fn const_eval_validated_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
// see comment in const_eval_raw_provider for what we're doing here
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_validated(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {
// Promoteds should never be "too generic" when getting evaluated.
// They either don't get evaluated, or we are in a monomorphic context
assert!(key.value.promoted.is_none());
}
// dedupliate calls
other => return other,
}
}
// We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
// Catch such calls and evaluate them instead of trying to load a constant's MIR.
if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
let ty = key.value.instance.ty(tcx);
let substs = match ty.kind {
ty::FnDef(_, substs) => substs,
_ => bug!("intrinsic with type {:?}", ty),
};
return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
let span = tcx.def_span(def_id);
let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
});
}
tcx.const_eval_raw(key).and_then(|val| validate_and_turn_into_const(tcx, val, key))
}
pub fn const_eval_raw_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
// Because the constant is computed twice (once per value of `Reveal`), we are at risk of
// reporting the same error twice here. To resolve this, we check whether we can evaluate the
// constant in the more restrictive `Reveal::UserFacing`, which most likely already was
// computed. For a large percentage of constants that will already have succeeded. Only
// associated constants of generic functions will fail due to not enough monomorphization
// information being available.
// In case we fail in the `UserFacing` variant, we just do the real computation.
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_raw(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {}
// dedupliate calls
other => return other,
}
}
if cfg!(debug_assertions) {
// Make sure we format the instance even if we do not print it.
// This serves as a regression test against an ICE on printing.
// The next two lines concatenated contain some discussion:
// https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
// subject/anon_const_instance_printing/near/135980032
let instance = key.value.instance.to_string();
trace!("const eval: {:?} ({})", key, instance);
}
let cid = key.value;
let def_id = cid.instance.def.def_id();
if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
return Err(ErrorHandled::Reported);
}
let is_static = tcx.is_static(def_id);
let span = tcx.def_span(cid.instance.def_id());
let mut ecx = InterpCx::new(
tcx.at(span),
key.param_env,
CompileTimeInterpreter::new(),
MemoryExtra { can_access_statics: is_static },
);
let res = ecx.load_mir(cid.instance.def, cid.promoted);
res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, *body))
.and_then(|place| {
Ok(RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
})
.map_err(|error| {
let err = error_to_const_error(&ecx, error);
// errors in statics are always emitted as fatal errors
if is_static {
// Ensure that if the above error was either `TooGeneric` or `Reported`
// an error must be reported.
let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
tcx.sess.delay_span_bug(
err.span,
&format!("static eval failure did not emit an error: {:#?}", v),
);
v
} else if def_id.is_local() {
// constant defined in this crate, we can figure out a lint level!
match tcx.def_kind(def_id) {
// constants never produce a hard error at the definition site. Anything else is
// a backwards compatibility hazard (and will break old versions of winapi for sure)
//
// note that validation may still cause a hard error on this very same constant,
// because any code that existed before validation could not have failed validation
// thus preventing such a hard error from being a backwards compatibility hazard
Some(DefKind::Const) | Some(DefKind::AssocConst) => {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
err.report_as_lint(
tcx.at(tcx.def_span(def_id)),
"any use of this value will cause an error",
hir_id,
Some(err.span),
)
}
// promoting runtime code is only allowed to error if it references broken constants
// any other kind of error will be reported to the user as a deny-by-default lint
_ => {
if let Some(p) = cid.promoted {
let span = tcx.promoted_mir(def_id)[p].span;
if let err_inval!(ReferencedConstant) = err.error {
err.report_as_error(
tcx.at(span),
"evaluation of constant expression failed",
)
} else {
err.report_as_lint(
tcx.at(span),
"reaching this expression at runtime will panic or abort",
tcx.hir().as_local_hir_id(def_id).unwrap(),
Some(err.span),
)
}
// anything else (array lengths, enum initializers, constant patterns) are reported
// as hard errors
} else {
err.report_as_error(ecx.tcx, "evaluation of constant value failed")
}
}
}
} else {
// use of broken constant from other crate
err.report_as_error(ecx.tcx, "could not evaluate constant")
}
})
}

16
src/librustc_mir/const_eval/error.rs
View File

@ -1,8 +1,8 @@
use std::error::Error;
use std::fmt;
use crate::interpret::InterpErrorInfo;
use super::InterpCx;
use crate::interpret::{ConstEvalErr, InterpErrorInfo, Machine};
#[derive(Clone, Debug)]
pub enum ConstEvalError {
NeedsRfc(String),
@ -28,3 +28,15 @@ impl fmt::Display for ConstEvalError {
}
impl Error for ConstEvalError {}
/// Turn an interpreter error into something to report to the user.
/// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
/// Should be called only if the error is actually going to to be reported!
pub fn error_to_const_error<'mir, 'tcx, M: Machine<'mir, 'tcx>>(
ecx: &InterpCx<'mir, 'tcx, M>,
mut error: InterpErrorInfo<'tcx>,
) -> ConstEvalErr<'tcx> {
error.print_backtrace();
let stacktrace = ecx.generate_stacktrace(None);
ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
}

216
src/librustc_mir/const_eval/query.rs Normal file
View File

@ -0,0 +1,216 @@
use crate::interpret::eval_nullary_intrinsic;
use rustc::hir::def::DefKind;
use rustc::mir::interpret::{ConstEvalErr, ErrorHandled};
use rustc::traits::Reveal;
use rustc::ty::{self, TyCtxt};
use crate::interpret::{ConstValue, GlobalId, InterpCx, RawConst, RefTracking};
use super::{
error_to_const_error, eval_body_using_ecx, mk_eval_cx, op_to_const, CompileTimeInterpreter,
};
pub fn note_on_undefined_behavior_error() -> &'static str {
"The rules on what exactly is undefined behavior aren't clear, \
so this check might be overzealous. Please open an issue on the rustc \
repository if you believe it should not be considered undefined behavior."
}
fn validate_and_turn_into_const<'tcx>(
tcx: TyCtxt<'tcx>,
constant: RawConst<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
let cid = key.value;
let def_id = cid.instance.def.def_id();
let is_static = tcx.is_static(def_id);
let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
let val = (|| {
let mplace = ecx.raw_const_to_mplace(constant)?;
let mut ref_tracking = RefTracking::new(mplace);
while let Some((mplace, path)) = ref_tracking.todo.pop() {
ecx.validate_operand(mplace.into(), path, Some(&mut ref_tracking))?;
}
// Now that we validated, turn this into a proper constant.
// Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
// whether they become immediates.
if is_static || cid.promoted.is_some() {
let ptr = mplace.ptr.to_ptr()?;
Ok(tcx.mk_const(ty::Const {
val: ty::ConstKind::Value(ConstValue::ByRef {
alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
offset: ptr.offset,
}),
ty: mplace.layout.ty,
}))
} else {
Ok(op_to_const(&ecx, mplace.into()))
}
})();
val.map_err(|error| {
let err = error_to_const_error(&ecx, error);
match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
Ok(mut diag) => {
diag.note(note_on_undefined_behavior_error());
diag.emit();
ErrorHandled::Reported
}
Err(err) => err,
}
})
}
pub fn const_eval_validated_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
// see comment in const_eval_raw_provider for what we're doing here
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_validated(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {
// Promoteds should never be "too generic" when getting evaluated.
// They either don't get evaluated, or we are in a monomorphic context
assert!(key.value.promoted.is_none());
}
// dedupliate calls
other => return other,
}
}
// We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
// Catch such calls and evaluate them instead of trying to load a constant's MIR.
if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
let ty = key.value.instance.ty(tcx);
let substs = match ty.kind {
ty::FnDef(_, substs) => substs,
_ => bug!("intrinsic with type {:?}", ty),
};
return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
let span = tcx.def_span(def_id);
let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
});
}
tcx.const_eval_raw(key).and_then(|val| validate_and_turn_into_const(tcx, val, key))
}
pub fn const_eval_raw_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
// Because the constant is computed twice (once per value of `Reveal`), we are at risk of
// reporting the same error twice here. To resolve this, we check whether we can evaluate the
// constant in the more restrictive `Reveal::UserFacing`, which most likely already was
// computed. For a large percentage of constants that will already have succeeded. Only
// associated constants of generic functions will fail due to not enough monomorphization
// information being available.
// In case we fail in the `UserFacing` variant, we just do the real computation.
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_raw(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {}
// dedupliate calls
other => return other,
}
}
if cfg!(debug_assertions) {
// Make sure we format the instance even if we do not print it.
// This serves as a regression test against an ICE on printing.
// The next two lines concatenated contain some discussion:
// https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
// subject/anon_const_instance_printing/near/135980032
let instance = key.value.instance.to_string();
trace!("const eval: {:?} ({})", key, instance);
}
let cid = key.value;
let def_id = cid.instance.def.def_id();
if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
return Err(ErrorHandled::Reported);
}
let is_static = tcx.is_static(def_id);
let span = tcx.def_span(cid.instance.def_id());
let mut ecx = InterpCx::new(
tcx.at(span),
key.param_env,
CompileTimeInterpreter::new(),
MemoryExtra { can_access_statics: is_static },
);
let res = ecx.load_mir(cid.instance.def, cid.promoted);
res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, *body))
.and_then(|place| {
Ok(RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
})
.map_err(|error| {
let err = error_to_const_error(&ecx, error);
// errors in statics are always emitted as fatal errors
if is_static {
// Ensure that if the above error was either `TooGeneric` or `Reported`
// an error must be reported.
let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
tcx.sess.delay_span_bug(
err.span,
&format!("static eval failure did not emit an error: {:#?}", v),
);
v
} else if def_id.is_local() {
// constant defined in this crate, we can figure out a lint level!
match tcx.def_kind(def_id) {
// constants never produce a hard error at the definition site. Anything else is
// a backwards compatibility hazard (and will break old versions of winapi for sure)
//
// note that validation may still cause a hard error on this very same constant,
// because any code that existed before validation could not have failed validation
// thus preventing such a hard error from being a backwards compatibility hazard
Some(DefKind::Const) | Some(DefKind::AssocConst) => {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
err.report_as_lint(
tcx.at(tcx.def_span(def_id)),
"any use of this value will cause an error",
hir_id,
Some(err.span),
)
}
// promoting runtime code is only allowed to error if it references broken constants
// any other kind of error will be reported to the user as a deny-by-default lint
_ => {
if let Some(p) = cid.promoted {
let span = tcx.promoted_mir(def_id)[p].span;
if let err_inval!(ReferencedConstant) = err.error {
err.report_as_error(
tcx.at(span),
"evaluation of constant expression failed",
)
} else {
err.report_as_lint(
tcx.at(span),
"reaching this expression at runtime will panic or abort",
tcx.hir().as_local_hir_id(def_id).unwrap(),
Some(err.span),
)
}
// anything else (array lengths, enum initializers, constant patterns) are reported
// as hard errors
} else {
err.report_as_error(ecx.tcx, "evaluation of constant value failed")
}
}
}
} else {
// use of broken constant from other crate
err.report_as_error(ecx.tcx, "could not evaluate constant")
}
})
}