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Various const eval cleanups #116835

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Oct 23, 2023
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121 changes: 72 additions & 49 deletions compiler/rustc_const_eval/src/const_eval/eval_queries.rs
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This is just outlining, right? These new functions only have a single call site?

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yes

Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ use std::mem;
use either::{Left, Right};

use rustc_hir::def::DefKind;
use rustc_middle::mir::interpret::{ErrorHandled, InterpErrorInfo};
use rustc_middle::mir::interpret::{AllocId, ErrorHandled, InterpErrorInfo};
use rustc_middle::mir::pretty::write_allocation_bytes;
use rustc_middle::mir::{self, ConstAlloc, ConstValue};
use rustc_middle::traits::Reveal;
Expand Down Expand Up @@ -285,15 +285,22 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
let def = cid.instance.def.def_id();
let is_static = tcx.is_static(def);

let mut ecx = InterpCx::new(
let ecx = InterpCx::new(
tcx,
tcx.def_span(def),
key.param_env,
// Statics (and promoteds inside statics) may access other statics, because unlike consts
// they do not have to behave "as if" they were evaluated at runtime.
CompileTimeInterpreter::new(CanAccessStatics::from(is_static), CheckAlignment::Error),
);
eval_in_interpreter(ecx, cid, is_static)
}

pub fn eval_in_interpreter<'mir, 'tcx>(
mut ecx: InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
cid: GlobalId<'tcx>,
is_static: bool,
) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
let res = ecx.load_mir(cid.instance.def, cid.promoted);
match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
Err(error) => {
Expand All @@ -306,7 +313,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
// If the current item has generics, we'd like to enrich the message with the
// instance and its args: to show the actual compile-time values, in addition to
// the expression, leading to the const eval error.
let instance = &key.value.instance;
let instance = &cid.instance;
if !instance.args.is_empty() {
let instance = with_no_trimmed_paths!(instance.to_string());
("const_with_path", instance)
Expand All @@ -331,60 +338,76 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
Ok(mplace) => {
// Since evaluation had no errors, validate the resulting constant.
// This is a separate `try` block to provide more targeted error reporting.
let validation: Result<_, InterpErrorInfo<'_>> = try {
let mut ref_tracking = RefTracking::new(mplace.clone());
let mut inner = false;
while let Some((mplace, path)) = ref_tracking.todo.pop() {
let mode = match tcx.static_mutability(cid.instance.def_id()) {
Some(_) if cid.promoted.is_some() => {
// Promoteds in statics are allowed to point to statics.
CtfeValidationMode::Const { inner, allow_static_ptrs: true }
}
Some(_) => CtfeValidationMode::Regular, // a `static`
None => CtfeValidationMode::Const { inner, allow_static_ptrs: false },
};
ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
inner = true;
}
};
let validation =
const_validate_mplace(&ecx, &mplace, is_static, cid.promoted.is_some());

let alloc_id = mplace.ptr().provenance.unwrap();

// Validation failed, report an error.
if let Err(error) = validation {
let (error, backtrace) = error.into_parts();
backtrace.print_backtrace();

let ub_note = matches!(error, InterpError::UndefinedBehavior(_)).then(|| {});

let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner();
let mut bytes = String::new();
if alloc.size() != abi::Size::ZERO {
bytes = "\n".into();
// FIXME(translation) there might be pieces that are translatable.
write_allocation_bytes(*ecx.tcx, alloc, &mut bytes, " ").unwrap();
}
let raw_bytes = errors::RawBytesNote {
size: alloc.size().bytes(),
align: alloc.align.bytes(),
bytes,
};

Err(super::report(
*ecx.tcx,
error,
None,
|| super::get_span_and_frames(&ecx),
move |span, frames| errors::UndefinedBehavior {
span,
ub_note,
frames,
raw_bytes,
},
))
Err(const_report_error(&ecx, error, alloc_id))
} else {
// Convert to raw constant
Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })
}
}
}
}

#[inline(always)]
pub fn const_validate_mplace<'mir, 'tcx>(
ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
mplace: &MPlaceTy<'tcx>,
is_static: bool,
is_promoted: bool,
) -> InterpResult<'tcx> {
let mut ref_tracking = RefTracking::new(mplace.clone());
let mut inner = false;
while let Some((mplace, path)) = ref_tracking.todo.pop() {
let mode = if is_static {
if is_promoted {
// Promoteds in statics are allowed to point to statics.
CtfeValidationMode::Const { inner, allow_static_ptrs: true }
} else {
// a `static`
CtfeValidationMode::Regular
}
} else {
CtfeValidationMode::Const { inner, allow_static_ptrs: false }
};
ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?;
inner = true;
}

Ok(())
}

#[inline(always)]
pub fn const_report_error<'mir, 'tcx>(
ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
error: InterpErrorInfo<'tcx>,
alloc_id: AllocId,
) -> ErrorHandled {
let (error, backtrace) = error.into_parts();
backtrace.print_backtrace();

let ub_note = matches!(error, InterpError::UndefinedBehavior(_)).then(|| {});

let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner();
let mut bytes = String::new();
if alloc.size() != abi::Size::ZERO {
bytes = "\n".into();
// FIXME(translation) there might be pieces that are translatable.
write_allocation_bytes(*ecx.tcx, alloc, &mut bytes, " ").unwrap();
}
let raw_bytes =
errors::RawBytesNote { size: alloc.size().bytes(), align: alloc.align.bytes(), bytes };

crate::const_eval::report(
*ecx.tcx,
error,
None,
|| crate::const_eval::get_span_and_frames(ecx),
move |span, frames| errors::UndefinedBehavior { span, ub_note, frames, raw_bytes },
)
}
15 changes: 6 additions & 9 deletions compiler/rustc_const_eval/src/interpret/eval_context.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1074,17 +1074,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
instance: ty::Instance<'tcx>,
) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> {
let gid = GlobalId { instance, promoted: None };
// For statics we pick `ParamEnv::reveal_all`, because statics don't have generics
// and thus don't care about the parameter environment. While we could just use
// `self.param_env`, that would mean we invoke the query to evaluate the static
// with different parameter environments, thus causing the static to be evaluated
// multiple times.
let param_env = if self.tcx.is_static(gid.instance.def_id()) {
ty::ParamEnv::reveal_all()
let val = if self.tcx.is_static(gid.instance.def_id()) {
let alloc_id = self.tcx.reserve_and_set_static_alloc(gid.instance.def_id());
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Ah, clever!
Could you a comment explaining why we're doing it this way?

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In particular, this doesn't actually add the assertion that eval_to_allocation_raw is never called on statics, or does it?

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No, because that isn't true in this PR yet.


let ty = instance.ty(self.tcx.tcx, self.param_env);
mir::ConstAlloc { alloc_id, ty }
} else {
self.param_env
self.ctfe_query(|tcx| tcx.eval_to_allocation_raw(self.param_env.and(gid)))?
};
let val = self.ctfe_query(|tcx| tcx.eval_to_allocation_raw(param_env.and(gid)))?;
self.raw_const_to_mplace(val)
}

Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_const_eval/src/interpret/validity.rs
Original file line number Diff line number Diff line change
Expand Up @@ -929,7 +929,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
/// - no pointers to statics.
/// - no `UnsafeCell` or non-ZST `&mut`.
#[inline(always)]
pub fn const_validate_operand(
pub(crate) fn const_validate_operand(
&self,
op: &OpTy<'tcx, M::Provenance>,
path: Vec<PathElem>,
Expand Down
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