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Auto merge of #116692 - Nadrieril:half-open-ranges, r=cjgillot
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Match usize/isize exhaustively with half-open ranges

The long-awaited finale to the saga of [exhaustiveness checking for integers](#50912)!

```rust
match 0usize {
    0.. => {} // exhaustive!
}
match 0usize {
    0..usize::MAX => {} // helpful error message!
}
```

Features:
- Half-open ranges behave as expected for `usize`/`isize`;
- Trying to use `0..usize::MAX` will tell you that `usize::MAX..` is missing and explain why. No more unhelpful "`_` is missing";
- Everything else stays the same.

This should unblock #37854.

Review-wise:
- I recommend looking commit-by-commit;
- This regresses perf because of the added complexity in `IntRange`; hopefully not too much;
- I measured each `#[inline]`, they all help a bit with the perf regression (tho I don't get why);
- I did not touch MIR building; I expect there's an easy PR there that would skip unnecessary comparisons when the range is half-open.
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bors committed Nov 1, 2023
2 parents 98f5ebb + 35fe75d commit 7fc6365
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249 changes: 239 additions & 10 deletions compiler/rustc_middle/src/thir.rs
Original file line number Diff line number Diff line change
Expand Up @@ -16,17 +16,19 @@ use rustc_hir::RangeEnd;
use rustc_index::newtype_index;
use rustc_index::IndexVec;
use rustc_middle::middle::region;
use rustc_middle::mir::interpret::AllocId;
use rustc_middle::mir::interpret::{AllocId, Scalar};
use rustc_middle::mir::{self, BinOp, BorrowKind, FakeReadCause, Mutability, UnOp};
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::layout::IntegerExt;
use rustc_middle::ty::{
self, AdtDef, CanonicalUserType, CanonicalUserTypeAnnotation, FnSig, GenericArgsRef, List, Ty,
UpvarArgs,
TyCtxt, UpvarArgs,
};
use rustc_span::def_id::LocalDefId;
use rustc_span::{sym, ErrorGuaranteed, Span, Symbol, DUMMY_SP};
use rustc_target::abi::{FieldIdx, VariantIdx};
use rustc_target::abi::{FieldIdx, Integer, Size, VariantIdx};
use rustc_target::asm::InlineAsmRegOrRegClass;
use std::cmp::Ordering;
use std::fmt;
use std::ops::Index;

Expand Down Expand Up @@ -810,12 +812,243 @@ pub enum PatKind<'tcx> {
Error(ErrorGuaranteed),
}

/// A range pattern.
/// The boundaries must be of the same type and that type must be numeric.
#[derive(Clone, Debug, PartialEq, HashStable, TypeVisitable)]
pub struct PatRange<'tcx> {
pub lo: mir::Const<'tcx>,
pub hi: mir::Const<'tcx>,
pub lo: PatRangeBoundary<'tcx>,
pub hi: PatRangeBoundary<'tcx>,
#[type_visitable(ignore)]
pub end: RangeEnd,
pub ty: Ty<'tcx>,
}

impl<'tcx> PatRange<'tcx> {
/// Whether this range covers the full extent of possible values (best-effort, we ignore floats).
#[inline]
pub fn is_full_range(&self, tcx: TyCtxt<'tcx>) -> Option<bool> {
let (min, max, size, bias) = match *self.ty.kind() {
ty::Char => (0, std::char::MAX as u128, Size::from_bits(32), 0),
ty::Int(ity) => {
let size = Integer::from_int_ty(&tcx, ity).size();
let max = size.truncate(u128::MAX);
let bias = 1u128 << (size.bits() - 1);
(0, max, size, bias)
}
ty::Uint(uty) => {
let size = Integer::from_uint_ty(&tcx, uty).size();
let max = size.unsigned_int_max();
(0, max, size, 0)
}
_ => return None,
};

// We want to compare ranges numerically, but the order of the bitwise representation of
// signed integers does not match their numeric order. Thus, to correct the ordering, we
// need to shift the range of signed integers to correct the comparison. This is achieved by
// XORing with a bias (see pattern/deconstruct_pat.rs for another pertinent example of this
// pattern).
//
// Also, for performance, it's important to only do the second `try_to_bits` if necessary.
let lo_is_min = match self.lo {
PatRangeBoundary::NegInfinity => true,
PatRangeBoundary::Finite(value) => {
let lo = value.try_to_bits(size).unwrap() ^ bias;
lo <= min
}
PatRangeBoundary::PosInfinity => false,
};
if lo_is_min {
let hi_is_max = match self.hi {
PatRangeBoundary::NegInfinity => false,
PatRangeBoundary::Finite(value) => {
let hi = value.try_to_bits(size).unwrap() ^ bias;
hi > max || hi == max && self.end == RangeEnd::Included
}
PatRangeBoundary::PosInfinity => true,
};
if hi_is_max {
return Some(true);
}
}
Some(false)
}

#[inline]
pub fn contains(
&self,
value: mir::Const<'tcx>,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<bool> {
use Ordering::*;
debug_assert_eq!(self.ty, value.ty());
let ty = self.ty;
let value = PatRangeBoundary::Finite(value);
// For performance, it's important to only do the second comparison if necessary.
Some(
match self.lo.compare_with(value, ty, tcx, param_env)? {
Less | Equal => true,
Greater => false,
} && match value.compare_with(self.hi, ty, tcx, param_env)? {
Less => true,
Equal => self.end == RangeEnd::Included,
Greater => false,
},
)
}

#[inline]
pub fn overlaps(
&self,
other: &Self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<bool> {
use Ordering::*;
debug_assert_eq!(self.ty, other.ty);
// For performance, it's important to only do the second comparison if necessary.
Some(
match other.lo.compare_with(self.hi, self.ty, tcx, param_env)? {
Less => true,
Equal => self.end == RangeEnd::Included,
Greater => false,
} && match self.lo.compare_with(other.hi, self.ty, tcx, param_env)? {
Less => true,
Equal => other.end == RangeEnd::Included,
Greater => false,
},
)
}
}

impl<'tcx> fmt::Display for PatRange<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
if let PatRangeBoundary::Finite(value) = &self.lo {
write!(f, "{value}")?;
}
if let PatRangeBoundary::Finite(value) = &self.hi {
write!(f, "{}", self.end)?;
write!(f, "{value}")?;
} else {
// `0..` is parsed as an inclusive range, we must display it correctly.
write!(f, "..")?;
}
Ok(())
}
}

/// A (possibly open) boundary of a range pattern.
/// If present, the const must be of a numeric type.
#[derive(Copy, Clone, Debug, PartialEq, HashStable, TypeVisitable)]
pub enum PatRangeBoundary<'tcx> {
Finite(mir::Const<'tcx>),
NegInfinity,
PosInfinity,
}

impl<'tcx> PatRangeBoundary<'tcx> {
#[inline]
pub fn is_finite(self) -> bool {
matches!(self, Self::Finite(..))
}
#[inline]
pub fn as_finite(self) -> Option<mir::Const<'tcx>> {
match self {
Self::Finite(value) => Some(value),
Self::NegInfinity | Self::PosInfinity => None,
}
}
#[inline]
pub fn to_const(self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> mir::Const<'tcx> {
match self {
Self::Finite(value) => value,
Self::NegInfinity => {
// Unwrap is ok because the type is known to be numeric.
let c = ty.numeric_min_val(tcx).unwrap();
mir::Const::from_ty_const(c, tcx)
}
Self::PosInfinity => {
// Unwrap is ok because the type is known to be numeric.
let c = ty.numeric_max_val(tcx).unwrap();
mir::Const::from_ty_const(c, tcx)
}
}
}
pub fn eval_bits(self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> u128 {
match self {
Self::Finite(value) => value.eval_bits(tcx, param_env),
Self::NegInfinity => {
// Unwrap is ok because the type is known to be numeric.
ty.numeric_min_and_max_as_bits(tcx).unwrap().0
}
Self::PosInfinity => {
// Unwrap is ok because the type is known to be numeric.
ty.numeric_min_and_max_as_bits(tcx).unwrap().1
}
}
}

#[instrument(skip(tcx, param_env), level = "debug", ret)]
pub fn compare_with(
self,
other: Self,
ty: Ty<'tcx>,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<Ordering> {
use PatRangeBoundary::*;
match (self, other) {
// When comparing with infinities, we must remember that `0u8..` and `0u8..=255`
// describe the same range. These two shortcuts are ok, but for the rest we must check
// bit values.
(PosInfinity, PosInfinity) => return Some(Ordering::Equal),
(NegInfinity, NegInfinity) => return Some(Ordering::Equal),

// This code is hot when compiling matches with many ranges. So we
// special-case extraction of evaluated scalars for speed, for types where
// raw data comparisons are appropriate. E.g. `unicode-normalization` has
// many ranges such as '\u{037A}'..='\u{037F}', and chars can be compared
// in this way.
(Finite(mir::Const::Ty(a)), Finite(mir::Const::Ty(b)))
if matches!(ty.kind(), ty::Uint(_) | ty::Char) =>
{
return Some(a.kind().cmp(&b.kind()));
}
(
Finite(mir::Const::Val(mir::ConstValue::Scalar(Scalar::Int(a)), _)),
Finite(mir::Const::Val(mir::ConstValue::Scalar(Scalar::Int(b)), _)),
) if matches!(ty.kind(), ty::Uint(_) | ty::Char) => return Some(a.cmp(&b)),
_ => {}
}

let a = self.eval_bits(ty, tcx, param_env);
let b = other.eval_bits(ty, tcx, param_env);

match ty.kind() {
ty::Float(ty::FloatTy::F32) => {
use rustc_apfloat::Float;
let a = rustc_apfloat::ieee::Single::from_bits(a);
let b = rustc_apfloat::ieee::Single::from_bits(b);
a.partial_cmp(&b)
}
ty::Float(ty::FloatTy::F64) => {
use rustc_apfloat::Float;
let a = rustc_apfloat::ieee::Double::from_bits(a);
let b = rustc_apfloat::ieee::Double::from_bits(b);
a.partial_cmp(&b)
}
ty::Int(ity) => {
use rustc_middle::ty::layout::IntegerExt;
let size = rustc_target::abi::Integer::from_int_ty(&tcx, *ity).size();
let a = size.sign_extend(a) as i128;
let b = size.sign_extend(b) as i128;
Some(a.cmp(&b))
}
ty::Uint(_) | ty::Char => Some(a.cmp(&b)),
_ => bug!(),
}
}
}

impl<'tcx> fmt::Display for Pat<'tcx> {
Expand Down Expand Up @@ -944,11 +1177,7 @@ impl<'tcx> fmt::Display for Pat<'tcx> {
PatKind::InlineConstant { def: _, ref subpattern } => {
write!(f, "{} (from inline const)", subpattern)
}
PatKind::Range(box PatRange { lo, hi, end }) => {
write!(f, "{lo}")?;
write!(f, "{end}")?;
write!(f, "{hi}")
}
PatKind::Range(ref range) => write!(f, "{range}"),
PatKind::Slice { ref prefix, ref slice, ref suffix }
| PatKind::Array { ref prefix, ref slice, ref suffix } => {
write!(f, "[")?;
Expand Down
78 changes: 43 additions & 35 deletions compiler/rustc_middle/src/ty/util.rs
Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ use rustc_index::bit_set::GrowableBitSet;
use rustc_macros::HashStable;
use rustc_session::Limit;
use rustc_span::sym;
use rustc_target::abi::{Integer, IntegerType, Size};
use rustc_target::abi::{Integer, IntegerType, Primitive, Size};
use rustc_target::spec::abi::Abi;
use smallvec::SmallVec;
use std::{fmt, iter};
Expand Down Expand Up @@ -919,54 +919,62 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for OpaqueTypeExpander<'tcx> {
}

impl<'tcx> Ty<'tcx> {
/// Returns the `Size` for primitive types (bool, uint, int, char, float).
pub fn primitive_size(self, tcx: TyCtxt<'tcx>) -> Size {
match *self.kind() {
ty::Bool => Size::from_bytes(1),
ty::Char => Size::from_bytes(4),
ty::Int(ity) => Integer::from_int_ty(&tcx, ity).size(),
ty::Uint(uty) => Integer::from_uint_ty(&tcx, uty).size(),
ty::Float(ty::FloatTy::F32) => Primitive::F32.size(&tcx),
ty::Float(ty::FloatTy::F64) => Primitive::F64.size(&tcx),
_ => bug!("non primitive type"),
}
}

pub fn int_size_and_signed(self, tcx: TyCtxt<'tcx>) -> (Size, bool) {
let (int, signed) = match *self.kind() {
ty::Int(ity) => (Integer::from_int_ty(&tcx, ity), true),
ty::Uint(uty) => (Integer::from_uint_ty(&tcx, uty), false),
match *self.kind() {
ty::Int(ity) => (Integer::from_int_ty(&tcx, ity).size(), true),
ty::Uint(uty) => (Integer::from_uint_ty(&tcx, uty).size(), false),
_ => bug!("non integer discriminant"),
};
(int.size(), signed)
}
}

/// Returns the maximum value for the given numeric type (including `char`s)
/// or returns `None` if the type is not numeric.
pub fn numeric_max_val(self, tcx: TyCtxt<'tcx>) -> Option<ty::Const<'tcx>> {
let val = match self.kind() {
/// Returns the minimum and maximum values for the given numeric type (including `char`s) or
/// returns `None` if the type is not numeric.
pub fn numeric_min_and_max_as_bits(self, tcx: TyCtxt<'tcx>) -> Option<(u128, u128)> {
use rustc_apfloat::ieee::{Double, Single};
Some(match self.kind() {
ty::Int(_) | ty::Uint(_) => {
let (size, signed) = self.int_size_and_signed(tcx);
let val =
let min = if signed { size.truncate(size.signed_int_min() as u128) } else { 0 };
let max =
if signed { size.signed_int_max() as u128 } else { size.unsigned_int_max() };
Some(val)
(min, max)
}
ty::Char => Some(std::char::MAX as u128),
ty::Float(fty) => Some(match fty {
ty::FloatTy::F32 => rustc_apfloat::ieee::Single::INFINITY.to_bits(),
ty::FloatTy::F64 => rustc_apfloat::ieee::Double::INFINITY.to_bits(),
}),
_ => None,
};
ty::Char => (0, std::char::MAX as u128),
ty::Float(ty::FloatTy::F32) => {
((-Single::INFINITY).to_bits(), Single::INFINITY.to_bits())
}
ty::Float(ty::FloatTy::F64) => {
((-Double::INFINITY).to_bits(), Double::INFINITY.to_bits())
}
_ => return None,
})
}

val.map(|v| ty::Const::from_bits(tcx, v, ty::ParamEnv::empty().and(self)))
/// Returns the maximum value for the given numeric type (including `char`s)
/// or returns `None` if the type is not numeric.
pub fn numeric_max_val(self, tcx: TyCtxt<'tcx>) -> Option<ty::Const<'tcx>> {
self.numeric_min_and_max_as_bits(tcx)
.map(|(_, max)| ty::Const::from_bits(tcx, max, ty::ParamEnv::empty().and(self)))
}

/// Returns the minimum value for the given numeric type (including `char`s)
/// or returns `None` if the type is not numeric.
pub fn numeric_min_val(self, tcx: TyCtxt<'tcx>) -> Option<ty::Const<'tcx>> {
let val = match self.kind() {
ty::Int(_) | ty::Uint(_) => {
let (size, signed) = self.int_size_and_signed(tcx);
let val = if signed { size.truncate(size.signed_int_min() as u128) } else { 0 };
Some(val)
}
ty::Char => Some(0),
ty::Float(fty) => Some(match fty {
ty::FloatTy::F32 => (-::rustc_apfloat::ieee::Single::INFINITY).to_bits(),
ty::FloatTy::F64 => (-::rustc_apfloat::ieee::Double::INFINITY).to_bits(),
}),
_ => None,
};

val.map(|v| ty::Const::from_bits(tcx, v, ty::ParamEnv::empty().and(self)))
self.numeric_min_and_max_as_bits(tcx)
.map(|(min, _)| ty::Const::from_bits(tcx, min, ty::ParamEnv::empty().and(self)))
}

/// Checks whether values of this type `T` are *moved* or *copied*
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_mir_build/src/build/matches/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1035,7 +1035,7 @@ enum TestKind<'tcx> {
ty: Ty<'tcx>,
},

/// Test whether the value falls within an inclusive or exclusive range
/// Test whether the value falls within an inclusive or exclusive range.
Range(Box<PatRange<'tcx>>),

/// Test that the length of the slice is equal to `len`.
Expand Down
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