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Tell rustc about unused bits in Span. #93747

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Tell rustc about unused bits in Span. #93747

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2 changes: 1 addition & 1 deletion compiler/rustc_hir/src/hir.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3308,7 +3308,7 @@ mod size_asserts {
rustc_data_structures::static_assert_size!(super::QPath<'static>, 24);
rustc_data_structures::static_assert_size!(super::Ty<'static>, 80);

rustc_data_structures::static_assert_size!(super::Item<'static>, 184);
rustc_data_structures::static_assert_size!(super::Item<'static>, 176);
rustc_data_structures::static_assert_size!(super::TraitItem<'static>, 128);
rustc_data_structures::static_assert_size!(super::ImplItem<'static>, 152);
rustc_data_structures::static_assert_size!(super::ForeignItem<'static>, 136);
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1 change: 1 addition & 0 deletions compiler/rustc_span/src/lib.rs
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Expand Up @@ -22,6 +22,7 @@
#![feature(nll)]
#![feature(min_specialization)]
#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
#![feature(rustc_attrs)]

#[macro_use]
extern crate rustc_macros;
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22 changes: 16 additions & 6 deletions compiler/rustc_span/src/span_encoding.rs
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Expand Up @@ -72,16 +72,22 @@ use rustc_data_structures::fx::FxIndexSet;
// #[cfg_attr(not(bootstrap), rustc_pass_by_value)]
pub struct Span {
base_or_index: u32,
len_or_tag: u16,
len_or_tag: LenOrTag,
ctxt_or_zero: u16,
}

const LEN_TAG: u16 = 0b1000_0000_0000_0000;
// LEN_TAG allows for some extra values at the top. Declare them to rustc to use as niches.
#[rustc_layout_scalar_valid_range_end(0b1000_0000_0000_0000)]
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
struct LenOrTag(u16);

const LEN_TAG: LenOrTag = unsafe { LenOrTag(0b1000_0000_0000_0000) };
const MAX_LEN: u32 = 0b0111_1111_1111_1111;
const MAX_CTXT: u32 = 0b1111_1111_1111_1111;

/// Dummy span, both position and length are zero, syntax context is zero as well.
pub const DUMMY_SP: Span = Span { base_or_index: 0, len_or_tag: 0, ctxt_or_zero: 0 };
pub const DUMMY_SP: Span =
Span { base_or_index: 0, len_or_tag: unsafe { LenOrTag(0) }, ctxt_or_zero: 0 };

impl Span {
#[inline]
Expand All @@ -99,7 +105,11 @@ impl Span {

if len <= MAX_LEN && ctxt2 <= MAX_CTXT && parent.is_none() {
// Inline format.
Span { base_or_index: base, len_or_tag: len as u16, ctxt_or_zero: ctxt2 as u16 }
Span {
base_or_index: base,
len_or_tag: unsafe { LenOrTag(len as u16) },
ctxt_or_zero: ctxt2 as u16,
}
} else {
// Interned format.
let index =
Expand All @@ -123,10 +133,10 @@ impl Span {
pub fn data_untracked(self) -> SpanData {
if self.len_or_tag != LEN_TAG {
// Inline format.
debug_assert!(self.len_or_tag as u32 <= MAX_LEN);
debug_assert!(self.len_or_tag.0 as u32 <= MAX_LEN);
SpanData {
lo: BytePos(self.base_or_index),
hi: BytePos(self.base_or_index + self.len_or_tag as u32),
hi: BytePos(self.base_or_index + self.len_or_tag.0 as u32),
ctxt: SyntaxContext::from_u32(self.ctxt_or_zero as u32),
parent: None,
}
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