From eb4fc45310c70513d73d893616cd6735465680ca Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 3 Feb 2020 21:05:18 +0100
Subject: [PATCH] Use CachingSourceMapView::byte_pos_to_line_and_col instead of
 SourceMap::lookup_char_pos

The former calculates byte offsets instead of char offsets. It is faster
to calculate byte offsets than char offsets. Also most DWARF producers
and consumers use byte offsets instead of char offsets.
---
 src/debuginfo/line_info.rs | 23 ++++++++++++-----------
 src/debuginfo/mod.rs       |  6 ++++++
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/src/debuginfo/line_info.rs b/src/debuginfo/line_info.rs
index 3152e4812f7..66a12091ecd 100644
--- a/src/debuginfo/line_info.rs
+++ b/src/debuginfo/line_info.rs
@@ -3,7 +3,7 @@ use std::path::{Component, Path};
 
 use crate::prelude::*;
 
-use rustc_span::FileName;
+use rustc_span::{CachingSourceMapView, FileName};
 
 use cranelift_codegen::binemit::CodeOffset;
 
@@ -74,12 +74,12 @@ fn line_program_add_file(
 
 impl<'tcx> DebugContext<'tcx> {
     pub(super) fn emit_location(&mut self, entry_id: UnitEntryId, span: Span) {
-        let loc = self.tcx.sess.source_map().lookup_char_pos(span.lo());
+        let (file, line, col) = self.source_map.byte_pos_to_line_and_col(span.lo()).unwrap();
 
         let file_id = line_program_add_file(
             &mut self.dwarf.unit.line_program,
             &mut self.dwarf.line_strings,
-            &loc.file.name,
+            &file.name,
         );
 
         let entry = self.dwarf.unit.get_mut(entry_id);
@@ -90,12 +90,12 @@ impl<'tcx> DebugContext<'tcx> {
         );
         entry.set(
             gimli::DW_AT_decl_line,
-            AttributeValue::Udata(loc.line as u64),
+            AttributeValue::Udata(line as u64),
         );
         // FIXME: probably omit this
         entry.set(
             gimli::DW_AT_decl_column,
-            AttributeValue::Udata(loc.col.to_usize() as u64),
+            AttributeValue::Udata(col.to_usize() as u64),
         );
     }
 }
@@ -108,6 +108,7 @@ impl<'a, 'tcx> FunctionDebugContext<'a, 'tcx> {
         source_info_set: &indexmap::IndexSet<SourceInfo>,
     ) -> CodeOffset {
         let tcx = self.debug_context.tcx;
+        let mut source_map = CachingSourceMapView::new(tcx.sess.source_map());
 
         let line_program = &mut self.debug_context.dwarf.unit.line_program;
 
@@ -124,25 +125,25 @@ impl<'a, 'tcx> FunctionDebugContext<'a, 'tcx> {
         let line_strings = &mut self.debug_context.dwarf.line_strings;
         let mut last_file = None;
         let mut create_row_for_span = |line_program: &mut LineProgram, span: Span| {
-            let loc = tcx.sess.source_map().lookup_char_pos(span.lo());
+            let (file, line, col) = source_map.byte_pos_to_line_and_col(span.lo()).unwrap();
 
             // line_program_add_file is very slow.
             // Optimize for the common case of the current file not being changed.
             let current_file_changed = if let Some(last_file) = &mut last_file {
                 // If the allocations are not equal, then the files may still be equal, but that
                 // is not a problem, as this is just an optimization.
-                !Lrc::ptr_eq(last_file, &loc.file)
+                !Lrc::ptr_eq(last_file, &file)
             } else {
                 true
             };
             if current_file_changed {
-                let file_id = line_program_add_file(line_program, line_strings, &loc.file.name);
+                let file_id = line_program_add_file(line_program, line_strings, &file.name);
                 line_program.row().file = file_id;
-                last_file = Some(loc.file.clone());
+                last_file = Some(file.clone());
             }
 
-            line_program.row().line = loc.line as u64;
-            line_program.row().column = loc.col.to_u32() as u64 + 1;
+            line_program.row().line = line as u64;
+            line_program.row().column = col.to_u32() as u64 + 1;
             line_program.generate_row();
         };
 
diff --git a/src/debuginfo/mod.rs b/src/debuginfo/mod.rs
index d4be26885a0..f007cb1265d 100644
--- a/src/debuginfo/mod.rs
+++ b/src/debuginfo/mod.rs
@@ -3,6 +3,8 @@ mod line_info;
 
 use crate::prelude::*;
 
+use rustc_span::CachingSourceMapView;
+
 use cranelift_codegen::ir::{StackSlots, ValueLabel, ValueLoc};
 use cranelift_codegen::isa::RegUnit;
 use cranelift_codegen::ValueLocRange;
@@ -34,6 +36,8 @@ pub struct DebugContext<'tcx> {
     unit_range_list: RangeList,
 
     types: HashMap<Ty<'tcx>, UnitEntryId>,
+
+    source_map: CachingSourceMapView<'tcx>,
 }
 
 impl<'tcx> DebugContext<'tcx> {
@@ -98,6 +102,8 @@ impl<'tcx> DebugContext<'tcx> {
             unit_range_list: RangeList(Vec::new()),
 
             types: HashMap::new(),
+
+            source_map: CachingSourceMapView::new(tcx.sess.source_map()),
         }
     }