[Coverage] Const-ize MCDCRecordProcessor stuff (#78918)

The life of `MCDCRecordProcessor`'s instance is short. It may accept
`const` objects to process.

On the other hand, the life of `MCDCBranches` is shorter than `Record`.
It may be rewritten with reference, rather than copying.

Author: chapuni

llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h

@@ -587,8 +587,9 @@ class CounterMappingContext {
   /// Return an MCDC record that indicates executed test vectors and condition
   /// pairs.
   Expected<MCDCRecord>
-  evaluateMCDCRegion(CounterMappingRegion Region, BitVector Bitmap,
-                     ArrayRef<CounterMappingRegion> Branches);
+  evaluateMCDCRegion(const CounterMappingRegion &Region,
+                     const BitVector &Bitmap,
+                     ArrayRef<const CounterMappingRegion *> Branches);
 
   unsigned getMaxCounterID(const Counter &C) const;
 };

llvm/lib/ProfileData/Coverage/CoverageMapping.cpp

@@ -247,14 +247,14 @@ class MCDCRecordProcessor {
   /// Each index of the bitmap corresponds to a possible test vector. An index
   /// with a bit value of '1' indicates that the corresponding Test Vector
   /// identified by that index was executed.
-  BitVector &ExecutedTestVectorBitmap;
+  const BitVector &ExecutedTestVectorBitmap;
 
   /// Decision Region to which the ExecutedTestVectorBitmap applies.
-  CounterMappingRegion &Region;
+  const CounterMappingRegion &Region;
 
   /// Array of branch regions corresponding each conditions in the boolean
   /// expression.
-  ArrayRef<CounterMappingRegion> Branches;
+  ArrayRef<const CounterMappingRegion *> Branches;
 
   /// Total number of conditions in the boolean expression.
   unsigned NumConditions;
@@ -276,8 +276,9 @@ class MCDCRecordProcessor {
   MCDCRecord::TestVectors ExecVectors;
 
 public:
-  MCDCRecordProcessor(BitVector &Bitmap, CounterMappingRegion &Region,
-                      ArrayRef<CounterMappingRegion> Branches)
+  MCDCRecordProcessor(const BitVector &Bitmap,
+                      const CounterMappingRegion &Region,
+                      ArrayRef<const CounterMappingRegion *> Branches)
       : ExecutedTestVectorBitmap(Bitmap), Region(Region), Branches(Branches),
         NumConditions(Region.MCDCParams.NumConditions),
         Folded(NumConditions, false), IndependencePairs(NumConditions),
@@ -342,7 +343,7 @@ class MCDCRecordProcessor {
 
   /// Walk the bits in the bitmap.  A bit set to '1' indicates that the test
   /// vector at the corresponding index was executed during a test run.
-  void findExecutedTestVectors(BitVector &ExecutedTestVectorBitmap) {
+  void findExecutedTestVectors(const BitVector &ExecutedTestVectorBitmap) {
     for (unsigned Idx = 0; Idx < ExecutedTestVectorBitmap.size(); ++Idx) {
       if (ExecutedTestVectorBitmap[Idx] == 0)
         continue;
@@ -445,11 +446,11 @@ class MCDCRecordProcessor {
     //   visualize where the condition is.
     // - Record whether the condition is constant folded so that we exclude it
     //   from being measured.
-    for (const auto &B : Branches) {
-      Map[B.MCDCParams.ID] = &B;
-      PosToID[I] = B.MCDCParams.ID - 1;
-      CondLoc[I] = B.startLoc();
-      Folded[I++] = (B.Count.isZero() && B.FalseCount.isZero());
+    for (const auto *B : Branches) {
+      Map[B->MCDCParams.ID] = B;
+      PosToID[I] = B->MCDCParams.ID - 1;
+      CondLoc[I] = B->startLoc();
+      Folded[I++] = (B->Count.isZero() && B->FalseCount.isZero());
     }
 
     // Initialize a base test vector as 'DontCare'.
@@ -473,8 +474,9 @@ class MCDCRecordProcessor {
 };
 
 Expected<MCDCRecord> CounterMappingContext::evaluateMCDCRegion(
-    CounterMappingRegion Region, BitVector ExecutedTestVectorBitmap,
-    ArrayRef<CounterMappingRegion> Branches) {
+    const CounterMappingRegion &Region,
+    const BitVector &ExecutedTestVectorBitmap,
+    ArrayRef<const CounterMappingRegion *> Branches) {
 
   MCDCRecordProcessor MCDCProcessor(ExecutedTestVectorBitmap, Region, Branches);
   return MCDCProcessor.processMCDCRecord();
@@ -638,7 +640,7 @@ Error CoverageMapping::loadFunctionRecord(
 
   unsigned NumConds = 0;
   const CounterMappingRegion *MCDCDecision;
-  std::vector<CounterMappingRegion> MCDCBranches;
+  std::vector<const CounterMappingRegion *> MCDCBranches;
 
   FunctionRecord Function(OrigFuncName, Record.Filenames);
   for (const auto &Region : Record.MappingRegions) {
@@ -666,7 +668,7 @@ Error CoverageMapping::loadFunctionRecord(
     // correspond to it in a vector, according to the number of conditions
     // recorded for the region (tracked by NumConds).
     if (NumConds > 0 && Region.Kind == CounterMappingRegion::MCDCBranchRegion) {
-      MCDCBranches.push_back(Region);
+      MCDCBranches.push_back(&Region);
 
       // As we move through all of the MCDCBranchRegions that follow the
       // MCDCDecisionRegion, decrement NumConds to make sure we account for