diff options
| -rw-r--r-- | compiler/rustc_span/src/span_encoding.rs | 36 |
1 files changed, 21 insertions, 15 deletions
diff --git a/compiler/rustc_span/src/span_encoding.rs b/compiler/rustc_span/src/span_encoding.rs index 708ca43f4be..b3de6741594 100644 --- a/compiler/rustc_span/src/span_encoding.rs +++ b/compiler/rustc_span/src/span_encoding.rs @@ -28,12 +28,17 @@ use rustc_data_structures::fx::FxIndexSet; /// Inline (compressed) format: /// - `span.base_or_index == span_data.lo` /// - `span.len_or_tag == len == span_data.hi - span_data.lo` (must be `<= MAX_LEN`) -/// - `span.ctxt == span_data.ctxt` (must be `< MAX_CTXT`) +/// - `span.ctxt_or_tag == span_data.ctxt` (must be `<= MAX_CTXT`) +/// +/// Interned format with inline `SyntaxContext`: +/// - `span.base_or_index == index` (indexes into the interner table) +/// - `span.len_or_tag == LEN_TAG` (high bit set, all other bits are zero) +/// - `span.ctxt_or_tag == span_data.ctxt` (must be `<= MAX_CTXT`) /// /// Interned format: /// - `span.base_or_index == index` (indexes into the interner table) /// - `span.len_or_tag == LEN_TAG` (high bit set, all other bits are zero) -/// - `span.ctxt == span_data.ctxt` (must be < `MAX_CTXT`) or `MAX_CTXT` otherwise +/// - `span.ctxt_or_tag == CTXT_TAG` /// /// The inline form uses 0 for the tag value (rather than 1) so that we don't /// need to mask out the tag bit when getting the length, and so that the @@ -50,10 +55,10 @@ use rustc_data_structures::fx::FxIndexSet; /// at 3 or 4, and then it drops off quickly from 8 onwards. 15 bits is enough /// for 99.99%+ of cases, but larger values (sometimes 20+ bits) might occur /// dozens of times in a typical crate. -/// - `ctxt` is 16 bits in `Span` and 32 bits in `SpanData`, which means that +/// - `ctxt_or_tag` is 16 bits in `Span` and 32 bits in `SpanData`, which means that /// large `ctxt` values will cause interning. The number of bits needed for /// `ctxt` values depend partly on the crate size and partly on the form of -/// the code. No crates in `rustc-perf` need more than 15 bits for `ctxt`, +/// the code. No crates in `rustc-perf` need more than 15 bits for `ctxt_or_tag`, /// but larger crates might need more than 16 bits. /// /// In order to reliably use parented spans in incremental compilation, @@ -65,15 +70,16 @@ use rustc_data_structures::fx::FxIndexSet; pub struct Span { base_or_index: u32, len_or_tag: u16, - ctxt_or_max: u16, + ctxt_or_tag: u16, } const LEN_TAG: u16 = 0b1000_0000_0000_0000; const MAX_LEN: u32 = 0b0111_1111_1111_1111; -const MAX_CTXT: u32 = 0b1111_1111_1111_1111; +const CTXT_TAG: u32 = 0b1111_1111_1111_1111; +const MAX_CTXT: u32 = CTXT_TAG - 1; /// 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_max: 0 }; +pub const DUMMY_SP: Span = Span { base_or_index: 0, len_or_tag: 0, ctxt_or_tag: 0 }; impl Span { #[inline] @@ -89,15 +95,15 @@ impl Span { let (base, len, ctxt2) = (lo.0, hi.0 - lo.0, ctxt.as_u32()); - if len <= MAX_LEN && ctxt2 < MAX_CTXT && parent.is_none() { + 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_max: ctxt2 as u16 } + Span { base_or_index: base, len_or_tag: len as u16, ctxt_or_tag: ctxt2 as u16 } } else { // Interned format. let index = with_span_interner(|interner| interner.intern(&SpanData { lo, hi, ctxt, parent })); - let ctxt_or_max = if ctxt2 < MAX_CTXT { ctxt2 } else { MAX_CTXT } as u16; - Span { base_or_index: index, len_or_tag: LEN_TAG, ctxt_or_max } + let ctxt_or_tag = if ctxt2 <= MAX_CTXT { ctxt2 } else { CTXT_TAG } as u16; + Span { base_or_index: index, len_or_tag: LEN_TAG, ctxt_or_tag } } } @@ -120,7 +126,7 @@ impl Span { SpanData { lo: BytePos(self.base_or_index), hi: BytePos(self.base_or_index + self.len_or_tag as u32), - ctxt: SyntaxContext::from_u32(self.ctxt_or_max as u32), + ctxt: SyntaxContext::from_u32(self.ctxt_or_tag as u32), parent: None, } } else { @@ -133,10 +139,10 @@ impl Span { /// This function is used as a fast path when decoding the full `SpanData` is not necessary. #[inline] pub fn ctxt(self) -> SyntaxContext { - let ctxt_or_max = self.ctxt_or_max as u32; - if ctxt_or_max < MAX_CTXT { + let ctxt_or_tag = self.ctxt_or_tag as u32; + if ctxt_or_tag <= MAX_CTXT { // Inline format or interned format with inline ctxt. - SyntaxContext::from_u32(ctxt_or_max) + SyntaxContext::from_u32(ctxt_or_tag) } else { // Interned format. let index = self.base_or_index; |