[llvm] CoverageMappingWriter: Emit `Decision` before `Expansion` (PR #78966)

[NAKAMURA Takumi via llvm-commits]

https://github.com/chapuni created https://github.com/llvm/llvm-project/pull/78966

Test cases (for llvm) would be required.

https://godbolt.org/z/orE99Y7hT
```
foo:
  Expansion,File 0, 4:11 -> 4:12 = #0 (Expanded file = 1)
  Decision,File 0, 4:11 -> 4:20 = M:0, C:2
  Expansion,File 0, 4:19 -> 4:20 = #1 (Expanded file = 2)
  Branch,File 1, 1:14 -> 1:17 = #1, (#0 - #1) [1,2,0] 
  Branch,File 2, 1:14 -> 1:17 = #2, (#1 - #2) [2,0,0] 
```

To relax scanning record, tweak order by `Decision < Expansion`. Relevant to #77871 

>From 069bf8eb9250169a703f9afbb392626578f14bfa Mon Sep 17 00:00:00 2001
From: NAKAMURA Takumi <geek4civic at gmail.com>
Date: Sun, 21 Jan 2024 18:09:30 +0900
Subject: [PATCH] CoverageMappingWriter: Emit `Decision` before `Expansion`

---
 .../ProfileData/Coverage/CoverageMappingWriter.cpp  | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp b/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
index 1c7d8a8909c488..e8597676003a02 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
@@ -167,7 +167,18 @@ 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);
+    };
+
+    auto LHSKindKey = getKindKey(LHS.Kind);
+    auto RHSKindKey = getKindKey(RHS.Kind);
+
+    return LHSKindKey < RHSKindKey;
   });
 
   // Write out the fileid -> filename mapping.