!! (WIP) De-duplicate mappings

Author: Zalathar

compiler/rustc_codegen_llvm/src/coverageinfo/map_data.rs

@@ -160,7 +160,13 @@ impl<'tcx> FunctionCoverage<'tcx> {
             CovTerm::Zero => u8::MAX,
         };
         for mappings in self.mappings_per_file.values_mut() {
-            mappings.sort_by_key(|(mapping_kind, _)| mapping_kind_sort_key(mapping_kind));
+            mappings.sort_by(|(a, a_region), (b, b_region)| {
+                Ord::cmp(a_region, b_region)
+                    .then_with(|| Ord::cmp(&mapping_kind_sort_key(a), &mapping_kind_sort_key(b)))
+            });
+            mappings.dedup_by(|(b, b_region), (a, a_region)| {
+                a_region == b_region && ((a == b) || matches!(b, CovTerm::Zero))
+            });
         }
     }
 

tests/coverage-map/status-quo/issue-84561.cov-map

@@ -1,11 +1,10 @@
 Function name: <issue_84561::Foo as core::cmp::PartialEq>::eq
-Raw bytes (14): 0x[01, 01, 00, 02, 01, 04, 0a, 00, 13, 00, 00, 0a, 00, 13]
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 04, 0a, 00, 13]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 0
-Number of file 0 mappings: 2
+Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 4, 10) to (start + 0, 19)
-- Code(Zero) at (prev + 0, 10) to (start + 0, 19)
 
 Function name: <issue_84561::Foo as core::fmt::Debug>::fmt
 Raw bytes (29): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 89, 01, 09, 00, 25, 05, 00, 25, 00, 26, 02, 01, 09, 00, 0f, 07, 01, 05, 00, 06]