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move guaranteed{ne,eq} implementation to compile-time machine #76634

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merged 1 commit into from
Sep 17, 2020
Merged

move guaranteed{ne,eq} implementation to compile-time machine #76634

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71 changes: 68 additions & 3 deletions compiler/rustc_mir/src/const_eval/machine.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ use rustc_ast::Mutability;
use rustc_hir::def_id::DefId;
use rustc_middle::mir::AssertMessage;
use rustc_session::Limit;
use rustc_span::symbol::Symbol;
use rustc_span::symbol::{sym, Symbol};

use crate::interpret::{
self, compile_time_machine, AllocId, Allocation, Frame, GlobalId, ImmTy, InterpCx,
Expand Down Expand Up @@ -176,6 +176,38 @@ impl interpret::MayLeak for ! {
}
}

impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
fn guaranteed_eq(&mut self, a: Scalar, b: Scalar) -> bool {
match (a, b) {
// Comparisons between integers are always known.
(Scalar::Raw { .. }, Scalar::Raw { .. }) => a == b,
// Equality with integers can never be known for sure.
(Scalar::Raw { .. }, Scalar::Ptr(_)) | (Scalar::Ptr(_), Scalar::Raw { .. }) => false,
// FIXME: return `true` for when both sides are the same pointer, *except* that
// some things (like functions and vtables) do not have stable addresses
// so we need to be careful around them (see e.g. #73722).
(Scalar::Ptr(_), Scalar::Ptr(_)) => false,
}
}

fn guaranteed_ne(&mut self, a: Scalar, b: Scalar) -> bool {
match (a, b) {
// Comparisons between integers are always known.
(Scalar::Raw { .. }, Scalar::Raw { .. }) => a != b,
// Comparisons of abstract pointers with null pointers are known if the pointer
// is in bounds, because if they are in bounds, the pointer can't be null.
(Scalar::Raw { data: 0, .. }, Scalar::Ptr(ptr))
| (Scalar::Ptr(ptr), Scalar::Raw { data: 0, .. }) => !self.memory.ptr_may_be_null(ptr),
// Inequality with integers other than null can never be known for sure.
(Scalar::Raw { .. }, Scalar::Ptr(_)) | (Scalar::Ptr(_), Scalar::Raw { .. }) => false,
// FIXME: return `true` for at least some comparisons where we can reliably
// determine the result of runtime inequality tests at compile-time.
// Examples include comparison of addresses in different static items.
(Scalar::Ptr(_), Scalar::Ptr(_)) => false,
}
}
}

impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> {
compile_time_machine!(<'mir, 'tcx>);

Expand Down Expand Up @@ -234,12 +266,45 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
// Shared intrinsics.
if ecx.emulate_intrinsic(instance, args, ret)? {
return Ok(());
}
// An intrinsic that we do not support
let intrinsic_name = ecx.tcx.item_name(instance.def_id());
Err(ConstEvalErrKind::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into())

// CTFE-specific intrinsics.
let (dest, ret) = match ret {
None => {
return Err(ConstEvalErrKind::NeedsRfc(format!(
"calling intrinsic `{}`",
intrinsic_name
))
.into());
}
Some(p) => p,
};
match intrinsic_name {
sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {
let a = ecx.read_immediate(args[0])?.to_scalar()?;
let b = ecx.read_immediate(args[1])?.to_scalar()?;
let cmp = if intrinsic_name == sym::ptr_guaranteed_eq {
ecx.guaranteed_eq(a, b)
} else {
ecx.guaranteed_ne(a, b)
};
ecx.write_scalar(Scalar::from_bool(cmp), dest)?;
}
_ => {
return Err(ConstEvalErrKind::NeedsRfc(format!(
"calling intrinsic `{}`",
intrinsic_name
))
.into());
}
}

ecx.go_to_block(ret);
Ok(())
}

fn assert_panic(
Expand Down
43 changes: 2 additions & 41 deletions compiler/rustc_mir/src/interpret/intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,8 @@ crate fn eval_nullary_intrinsic<'tcx>(

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
/// Returns `true` if emulation happened.
/// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
/// intrinsic handling.
pub fn emulate_intrinsic(
&mut self,
instance: ty::Instance<'tcx>,
Expand Down Expand Up @@ -328,16 +330,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
let offset_ptr = ptr.ptr_wrapping_signed_offset(offset_bytes, self);
self.write_scalar(offset_ptr, dest)?;
}
sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {
let a = self.read_immediate(args[0])?.to_scalar()?;
let b = self.read_immediate(args[1])?.to_scalar()?;
let cmp = if intrinsic_name == sym::ptr_guaranteed_eq {
self.guaranteed_eq(a, b)
} else {
self.guaranteed_ne(a, b)
};
self.write_scalar(Scalar::from_bool(cmp), dest)?;
}
sym::ptr_offset_from => {
let a = self.read_immediate(args[0])?.to_scalar()?;
let b = self.read_immediate(args[1])?.to_scalar()?;
Expand Down Expand Up @@ -448,37 +440,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
Ok(true)
}

fn guaranteed_eq(&mut self, a: Scalar<M::PointerTag>, b: Scalar<M::PointerTag>) -> bool {
match (a, b) {
// Comparisons between integers are always known.
(Scalar::Raw { .. }, Scalar::Raw { .. }) => a == b,
// Equality with integers can never be known for sure.
(Scalar::Raw { .. }, Scalar::Ptr(_)) | (Scalar::Ptr(_), Scalar::Raw { .. }) => false,
// FIXME: return `true` for when both sides are the same pointer, *except* that
// some things (like functions and vtables) do not have stable addresses
// so we need to be careful around them.
(Scalar::Ptr(_), Scalar::Ptr(_)) => false,
}
}

fn guaranteed_ne(&mut self, a: Scalar<M::PointerTag>, b: Scalar<M::PointerTag>) -> bool {
match (a, b) {
// Comparisons between integers are always known.
(Scalar::Raw { .. }, Scalar::Raw { .. }) => a != b,
// Comparisons of abstract pointers with null pointers are known if the pointer
// is in bounds, because if they are in bounds, the pointer can't be null.
(Scalar::Raw { data: 0, .. }, Scalar::Ptr(ptr))
| (Scalar::Ptr(ptr), Scalar::Raw { data: 0, .. }) => !self.memory.ptr_may_be_null(ptr),
// Inequality with integers other than null can never be known for sure.
(Scalar::Raw { .. }, Scalar::Ptr(_)) | (Scalar::Ptr(_), Scalar::Raw { .. }) => false,
// FIXME: return `true` for at least some comparisons where we can reliably
// determine the result of runtime inequality tests at compile-time.
// Examples include comparison of addresses in static items, for these we can
// give reliable results.
(Scalar::Ptr(_), Scalar::Ptr(_)) => false,
}
}

pub fn exact_div(
&mut self,
a: ImmTy<'tcx, M::PointerTag>,
Expand Down