coverage: Simplify grouping of mappings by file

This removes an ad-hoc implementation of `group_by`.

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -8,6 +8,7 @@ use rustc_codegen_ssa::traits::ConstMethods;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
+use rustc_index::IndexVec;
 use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::coverage::CodeRegion;
@@ -163,34 +164,33 @@ fn encode_mappings_for_function(
  return Vec::new();
  }
 
- let mut virtual_file_mapping = Vec::new();
+ let mut virtual_file_mapping = IndexVec::<u32, u32>::new();
  let mut mapping_regions = Vec::with_capacity(counter_regions.len());
- let mut current_file_name = None;
- let mut current_file_id = 0;
-
- // Convert the list of (Counter, CodeRegion) pairs to an array of `CounterMappingRegion`, sorted
- // by filename and position. Capture any new files to compute the `CounterMappingRegion`s
- // `file_id` (indexing files referenced by the current function), and construct the
- // function-specific `virtual_file_mapping` from `file_id` to its index in the module's
- // `filenames` array.
+
+ // Sort the list of (counter, region) mapping pairs by region, so that they
+ // can be grouped by filename. Prepare file IDs for each filename, and
+ // prepare the mapping data so that we can pass it through FFI to LLVM.
  counter_regions.sort_by_key(|(_counter, region)| *region);
- for (counter, region) in counter_regions {
- let CodeRegion { file_name, start_line, start_col, end_line, end_col } = *region;
- let same_file = current_file_name.is_some_and(|p| p == file_name);
- if !same_file {
- if current_file_name.is_some() {
- current_file_id += 1;
- }
- current_file_name = Some(file_name);
- debug!(" file_id: {} = '{:?}'", current_file_id, file_name);
- let global_file_id = global_file_table.global_file_id_for_file_name(file_name);
- virtual_file_mapping.push(global_file_id);
- }
- {
- debug!("Adding counter {:?} to map for {:?}", counter, region);
+ for counter_regions_for_file in
+ counter_regions.group_by(|(_, a), (_, b)| a.file_name == b.file_name)
+ {
+ // Look up (or allocate) the global file ID for this filename.
+ let file_name = counter_regions_for_file[0].1.file_name;
+ let global_file_id = global_file_table.global_file_id_for_file_name(file_name);
+
+ // Associate that global file ID with a local file ID for this function.
+ let local_file_id: u32 = virtual_file_mapping.push(global_file_id);
+ debug!(" file id: local {local_file_id} => global {global_file_id} = '{file_name:?}'");
+
+ // For each counter/region pair in this function+file, convert it to a
+ // form suitable for FFI.
+ for &(counter, region) in counter_regions_for_file {
+ let CodeRegion { file_name: _, start_line, start_col, end_line, end_col } = *region;
+
+ debug!("Adding counter {counter:?} to map for {region:?}");
  mapping_regions.push(CounterMappingRegion::code_region(
  counter,
- current_file_id,
+ local_file_id,
  start_line,
  start_col,
  end_line,
@@ -202,7 +202,7 @@ fn encode_mappings_for_function(
  // Encode the function's coverage mappings into a buffer.
  llvm::build_byte_buffer(|buffer| {
  coverageinfo::write_mapping_to_buffer(
- virtual_file_mapping,
+ virtual_file_mapping.raw,
  expressions,
  mapping_regions,
  buffer,

compiler/rustc_codegen_llvm/src/lib.rs

@@ -10,6 +10,7 @@
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(never_type)]
+#![feature(slice_group_by)]
 #![feature(impl_trait_in_assoc_type)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]