CoverageMappingWriter: Emit `Decision` before `Expansion` (#78966)

To relax scanning record, tweak order by `Decision < Expansion`, or
`Expansion` could not be distinguished whether it belonged to `Decision`
or not.

Relevant to #77871

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp b/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
index 1c7d8a8..27727f2 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
@@ -167,7 +167,15 @@ void CoverageMappingWriter::write(raw_ostream &OS) {
       return LHS.FileID < RHS.FileID;
     if (LHS.startLoc() != RHS.startLoc())
       return LHS.startLoc() < RHS.startLoc();
-    return LHS.Kind < RHS.Kind;
+
+    // Put `Decision` before `Expansion`.
+    auto getKindKey = [](CounterMappingRegion::RegionKind Kind) {
+      return (Kind == CounterMappingRegion::MCDCDecisionRegion
+                  ? 2 * CounterMappingRegion::ExpansionRegion - 1
+                  : 2 * Kind);
+    };
+
+    return getKindKey(LHS.Kind) < getKindKey(RHS.Kind);
   });
 
   // Write out the fileid -> filename mapping.