[Coverage] MCDC: Move findIndependencePairs deferred into MCDCRecord (#121188)

The result of "Independence pairs" is not mergeable. This change makes
defers re-calculation of "Independence pairs" after merging test
vectors.

No apparent behavior changes.

Author: chapuni

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

@@ -35,6 +35,7 @@
 #include <cstdint>
 #include <iterator>
 #include <memory>
+#include <optional>
 #include <sstream>
 #include <string>
 #include <system_error>
@@ -448,19 +449,22 @@ struct MCDCRecord {
 private:
   CounterMappingRegion Region;
   TestVectors TV;
-  TVPairMap IndependencePairs;
+  std::optional<TVPairMap> IndependencePairs;
   BoolVector Folded;
   CondIDMap PosToID;
   LineColPairMap CondLoc;
 
 public:
   MCDCRecord(const CounterMappingRegion &Region, TestVectors &&TV,
-             TVPairMap &&IndependencePairs, BoolVector &&Folded,
-             CondIDMap &&PosToID, LineColPairMap &&CondLoc)
-      : Region(Region), TV(std::move(TV)),
-        IndependencePairs(std::move(IndependencePairs)),
-        Folded(std::move(Folded)), PosToID(std::move(PosToID)),
-        CondLoc(std::move(CondLoc)){};
+             BoolVector &&Folded, CondIDMap &&PosToID, LineColPairMap &&CondLoc)
+      : Region(Region), TV(std::move(TV)), Folded(std::move(Folded)),
+        PosToID(std::move(PosToID)), CondLoc(std::move(CondLoc)) {
+    findIndependencePairs();
+  }
+
+  // Compare executed test vectors against each other to find an independence
+  // pairs for each condition.  This processing takes the most time.
+  void findIndependencePairs();
 
   const CounterMappingRegion &getDecisionRegion() const { return Region; }
   unsigned getNumConditions() const {
@@ -493,10 +497,10 @@ struct MCDCRecord {
   /// TestVectors requires a translation from a ordinal position to actual
   /// condition ID. This is done via PosToID[].
   bool isConditionIndependencePairCovered(unsigned Condition) const {
+    assert(IndependencePairs);
     auto It = PosToID.find(Condition);
-    if (It != PosToID.end())
-      return IndependencePairs.contains(It->second);
-    llvm_unreachable("Condition ID without an Ordinal mapping");
+    assert(It != PosToID.end() && "Condition ID without an Ordinal mapping");
+    return IndependencePairs->contains(It->second);
   }
 
   /// Return the Independence Pair that covers the given condition. Because
@@ -506,7 +510,8 @@ struct MCDCRecord {
   /// via PosToID[].
   TVRowPair getConditionIndependencePair(unsigned Condition) {
     assert(isConditionIndependencePairCovered(Condition));
-    return IndependencePairs[PosToID[Condition]];
+    assert(IndependencePairs);
+    return (*IndependencePairs)[PosToID[Condition]];
   }
 
   float getPercentCovered() const {

llvm/lib/ProfileData/Coverage/CoverageMapping.cpp

@@ -221,6 +221,40 @@ Expected<int64_t> CounterMappingContext::evaluate(const Counter &C) const {
   return LastPoppedValue;
 }
 
+// Find an independence pair for each condition:
+// - The condition is true in one test and false in the other.
+// - The decision outcome is true one test and false in the other.
+// - All other conditions' values must be equal or marked as "don't care".
+void MCDCRecord::findIndependencePairs() {
+  if (IndependencePairs)
+    return;
+
+  IndependencePairs.emplace();
+
+  unsigned NumTVs = TV.size();
+  // Will be replaced to shorter expr.
+  unsigned TVTrueIdx = std::distance(
+      TV.begin(),
+      std::find_if(TV.begin(), TV.end(),
+                   [&](auto I) { return (I.second == MCDCRecord::MCDC_True); })
+
+  );
+  for (unsigned I = TVTrueIdx; I < NumTVs; ++I) {
+    const auto &[A, ACond] = TV[I];
+    assert(ACond == MCDCRecord::MCDC_True);
+    for (unsigned J = 0; J < TVTrueIdx; ++J) {
+      const auto &[B, BCond] = TV[J];
+      assert(BCond == MCDCRecord::MCDC_False);
+      // If the two vectors differ in exactly one condition, ignoring DontCare
+      // conditions, we have found an independence pair.
+      auto AB = A.getDifferences(B);
+      if (AB.count() == 1)
+        IndependencePairs->insert(
+            {AB.find_first(), std::make_pair(J + 1, I + 1)});
+    }
+  }
+}
+
 mcdc::TVIdxBuilder::TVIdxBuilder(const SmallVectorImpl<ConditionIDs> &NextIDs,
                                  int Offset)
     : Indices(NextIDs.size()) {
@@ -375,9 +409,6 @@ class MCDCRecordProcessor : NextIDsBuilder, mcdc::TVIdxBuilder {
   /// ExecutedTestVectorBitmap.
   MCDCRecord::TestVectors &ExecVectors;
 
-  /// Number of False items in ExecVectors
-  unsigned NumExecVectorsF;
-
 #ifndef NDEBUG
   DenseSet<unsigned> TVIdxs;
 #endif
@@ -447,34 +478,11 @@ class MCDCRecordProcessor : NextIDsBuilder, mcdc::TVIdxBuilder {
     // Fill ExecVectors order by False items and True items.
     // ExecVectors is the alias of ExecVectorsByCond[false], so
     // Append ExecVectorsByCond[true] on it.
-    NumExecVectorsF = ExecVectors.size();
     auto &ExecVectorsT = ExecVectorsByCond[true];
     ExecVectors.append(std::make_move_iterator(ExecVectorsT.begin()),
                        std::make_move_iterator(ExecVectorsT.end()));
   }
 
-  // Find an independence pair for each condition:
-  // - The condition is true in one test and false in the other.
-  // - The decision outcome is true one test and false in the other.
-  // - All other conditions' values must be equal or marked as "don't care".
-  void findIndependencePairs() {
-    unsigned NumTVs = ExecVectors.size();
-    for (unsigned I = NumExecVectorsF; I < NumTVs; ++I) {
-      const auto &[A, ACond] = ExecVectors[I];
-      assert(ACond == MCDCRecord::MCDC_True);
-      for (unsigned J = 0; J < NumExecVectorsF; ++J) {
-        const auto &[B, BCond] = ExecVectors[J];
-        assert(BCond == MCDCRecord::MCDC_False);
-        // If the two vectors differ in exactly one condition, ignoring DontCare
-        // conditions, we have found an independence pair.
-        auto AB = A.getDifferences(B);
-        if (AB.count() == 1)
-          IndependencePairs.insert(
-              {AB.find_first(), std::make_pair(J + 1, I + 1)});
-      }
-    }
-  }
-
 public:
   /// Process the MC/DC Record in order to produce a result for a boolean
   /// expression. This process includes tracking the conditions that comprise
@@ -510,13 +518,8 @@ class MCDCRecordProcessor : NextIDsBuilder, mcdc::TVIdxBuilder {
     // Using Profile Bitmap from runtime, mark the executed test vectors.
     findExecutedTestVectors();
 
-    // Compare executed test vectors against each other to find an independence
-    // pairs for each condition.  This processing takes the most time.
-    findIndependencePairs();
-
     // Record Test vectors, executed vectors, and independence pairs.
-    return MCDCRecord(Region, std::move(ExecVectors),
-                      std::move(IndependencePairs), std::move(Folded),
+    return MCDCRecord(Region, std::move(ExecVectors), std::move(Folded),
                       std::move(PosToID), std::move(CondLoc));
   }
 };