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compare_const_vals: add a special case for certain ranges.

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This commit removes the `a == b` early return, which isn't useful in
practice, and replaces it with one that helps matches with many ranges,
including char ranges.
This commit is contained in:
Nicholas Nethercote 2022-06-09 10:23:39 +10:00
parent 73c52b724a
commit bdbf9b297b
1 changed files with 19 additions and 4 deletions
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23
compiler/rustc_mir_build/src/thir/pattern/mod.rs
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@ -15,7 +15,9 @@ use rustc_hir::def::{CtorOf, DefKind, Res};
use rustc_hir::pat_util::EnumerateAndAdjustIterator;
use rustc_hir::RangeEnd;
use rustc_index::vec::Idx;
use rustc_middle::mir::interpret::{ErrorHandled, LitToConstError, LitToConstInput};
use rustc_middle::mir::interpret::{
ConstValue, ErrorHandled, LitToConstError, LitToConstInput, Scalar,
};
use rustc_middle::mir::{self, UserTypeProjection};
use rustc_middle::mir::{BorrowKind, Field, Mutability};
use rustc_middle::thir::{Ascription, BindingMode, FieldPat, LocalVarId, Pat, PatKind, PatRange};
@ -755,11 +757,24 @@ pub(crate) fn compare_const_vals<'tcx>(
) -> Option<Ordering> {
assert_eq!(a.ty(), b.ty());
if a == b {
return Some(Ordering::Equal);
let ty = a.ty();
// 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.
match ty.kind() {
ty::Float(_) | ty::Int(_) => {} // require special handling, see below
_ => match (a, b) {
(
mir::ConstantKind::Val(ConstValue::Scalar(Scalar::Int(a)), _a_ty),
mir::ConstantKind::Val(ConstValue::Scalar(Scalar::Int(b)), _b_ty),
) => return Some(a.cmp(&b)),
_ => {}
},
}
let ty = a.ty();
let a = a.eval_bits(tcx, param_env, ty);
let b = b.eval_bits(tcx, param_env, ty);