servo: Merge #8990 - Optimize `TextRun::advance_for_range` (from pcwalton:advance-for-range-optzns); r=mbrubeck

The combined effects of these optimizations move `advance_for_range` from #1 in the layout profile on all sites I tested to #2, #3, or #4, depending on the site.

r? @mbrubeck

Source-Repo: https://github.com/servo/servo
Source-Revision: 67c3cb37073068fe8be7b35b26469e2e329ce385

servo/components/gfx/text/glyph.rs

@@ -403,6 +403,9 @@ pub struct GlyphStore {
     /// `entry_buffer` point to locations in this data structure.
     detail_store: DetailedGlyphStore,
 
+    /// A cache of the advance of the entire glyph store.
+    total_advance: Au,
+
     /// Used to check if fast path should be used in glyph iteration.
     has_detailed_glyphs: bool,
     is_whitespace: bool,
@@ -427,6 +430,7 @@ impl<'a> GlyphStore {
         GlyphStore {
             entry_buffer: vec![GlyphEntry::initial(); length],
             detail_store: DetailedGlyphStore::new(),
+            total_advance: Au(0),
             has_detailed_glyphs: false,
             is_whitespace: is_whitespace,
             is_rtl: is_rtl,
@@ -443,6 +447,20 @@ impl<'a> GlyphStore {
 
     pub fn finalize_changes(&mut self) {
         self.detail_store.ensure_sorted();
+        self.cache_total_advance()
+    }
+
+    #[inline(never)]
+    fn cache_total_advance(&mut self) {
+        let mut total_advance = Au(0);
+        for glyph in self.iter_glyphs_for_char_range(&Range::new(CharIndex(0), self.char_len())) {
+            total_advance = total_advance + glyph.advance()
+        }
+        self.total_advance = total_advance
+    }
+
+    pub fn total_advance(&self) -> Au {
+        self.total_advance
     }
 
     /// Adds a single glyph. If `character` is present, this represents a single character;
@@ -532,7 +550,9 @@ impl<'a> GlyphStore {
 
     #[inline]
     pub fn advance_for_char_range(&self, rang: &Range<CharIndex>) -> Au {
-        if !self.has_detailed_glyphs {
+        if rang.begin() == CharIndex(0) && rang.end() == self.char_len() {
+            self.total_advance
+        } else if !self.has_detailed_glyphs {
             self.advance_for_char_range_simple_glyphs(rang)
         } else {
             self.advance_for_char_range_slow_path(rang)

servo/components/gfx/text/text_run.rs

@@ -6,6 +6,7 @@ use app_units::Au;
 use font::{Font, FontHandleMethods, FontMetrics, IS_WHITESPACE_SHAPING_FLAG, RunMetrics};
 use font::{ShapingOptions};
 use platform::font_template::FontTemplateData;
+use std::cell::Cell;
 use std::cmp::{Ordering, max};
 use std::slice::Iter;
 use std::sync::Arc;
@@ -13,6 +14,11 @@ use text::glyph::{CharIndex, GlyphStore};
 use util::range::Range;
 use util::vec::{Comparator, FullBinarySearchMethods};
 
+thread_local! {
+    static INDEX_OF_FIRST_GLYPH_RUN_CACHE: Cell<Option<(*const TextRun, CharIndex, usize)>> =
+        Cell::new(None)
+}
+
 /// A single "paragraph" of text in one font size and style.
 #[derive(Clone, Deserialize, Serialize)]
 pub struct TextRun {
@@ -26,6 +32,19 @@ pub struct TextRun {
     pub bidi_level: u8,
 }
 
+impl Drop for TextRun {
+    fn drop(&mut self) {
+        // Invalidate the glyph run cache if it was our text run that got freed.
+        INDEX_OF_FIRST_GLYPH_RUN_CACHE.with(|index_of_first_glyph_run_cache| {
+            if let Some((text_run_ptr, _, _)) = index_of_first_glyph_run_cache.get() {
+                if text_run_ptr == (self as *const TextRun) {
+                    index_of_first_glyph_run_cache.set(None);
+                }
+            }
+        })
+    }
+}
+
 /// A single series of glyphs within a text run.
 #[derive(Clone, Deserialize, Serialize)]
 pub struct GlyphRun {
@@ -248,6 +267,10 @@ impl<'a> TextRun {
     }
 
     pub fn advance_for_range(&self, range: &Range<CharIndex>) -> Au {
+        if range.is_empty() {
+            return Au(0)
+        }
+
         // TODO(Issue #199): alter advance direction for RTL
         // TODO(Issue #98): using inter-char and inter-word spacing settings when measuring text
         self.natural_word_slices_in_range(range)
@@ -279,7 +302,21 @@ impl<'a> TextRun {
 
     /// Returns the index of the first glyph run containing the given character index.
     fn index_of_first_glyph_run_containing(&self, index: CharIndex) -> Option<usize> {
-        (&**self.glyphs).binary_search_index_by(&index, CharIndexComparator)
+        let self_ptr = self as *const TextRun;
+        INDEX_OF_FIRST_GLYPH_RUN_CACHE.with(|index_of_first_glyph_run_cache| {
+            if let Some((last_text_run, last_index, last_result)) =
+                    index_of_first_glyph_run_cache.get() {
+                if last_text_run == self_ptr && last_index == index {
+                    return Some(last_result)
+                }
+            }
+
+            let result = (&**self.glyphs).binary_search_index_by(&index, CharIndexComparator);
+            if let Some(result) = result {
+                index_of_first_glyph_run_cache.set(Some((self_ptr, index, result)));
+            }
+            result
+        })
     }
 
     /// Returns an iterator that will iterate over all slices of glyphs that represent natural

servo/components/util/range.rs

@@ -22,15 +22,23 @@ pub trait Int:
     fn from_usize(n: usize) -> Option<Self>;
 }
 impl Int for isize {
+    #[inline]
     fn zero() -> isize { 0 }
+    #[inline]
     fn one() -> isize { 1 }
+    #[inline]
     fn max_value() -> isize { ::std::isize::MAX }
+    #[inline]
     fn from_usize(n: usize) -> Option<isize> { num_lib::NumCast::from(n) }
 }
 impl Int for usize {
+    #[inline]
     fn zero() -> usize { 0 }
+    #[inline]
     fn one() -> usize { 1 }
+    #[inline]
     fn max_value() -> usize { ::std::usize::MAX }
+    #[inline]
     fn from_usize(n: usize) -> Option<usize> { Some(n) }
 }
 
@@ -88,9 +96,13 @@ macro_rules! int_range_index {
         }
 
         impl $crate::range::Int for $Self_ {
+            #[inline]
             fn zero() -> $Self_ { $Self_($crate::range::Int::zero()) }
+            #[inline]
             fn one() -> $Self_ { $Self_($crate::range::Int::one()) }
+            #[inline]
             fn max_value() -> $Self_ { $Self_($crate::range::Int::max_value()) }
+            #[inline]
             fn from_usize(n: usize) -> Option<$Self_> { $crate::range::Int::from_usize(n).map($Self_) }
         }