InstrProf: Simplify counting a file's regions when writing coverage (NFC)

When writing a coverage mapping we iterate through the mapping regions
in order of FileID, but we were then repeatedly searching from the
beginning of the list to count the number of regions with a given
FileID.

It is simpler and more efficient to search forward from the current
iterator to find the number of regions.

llvm-svn: 218842

1 files changed, 24 insertions, 34 deletions

diff --git a/llvm/lib/ProfileData/CoverageMappingWriter.cpp b/llvm/lib/ProfileData/CoverageMappingWriter.cpp
index 15d3cd3d48d..6969c2a1242 100644
--- a/llvm/lib/ProfileData/CoverageMappingWriter.cpp
+++ b/llvm/lib/ProfileData/CoverageMappingWriter.cpp
@@ -76,19 +76,6 @@ public:
 };
 }
 
-/// \brief Return the number of regions that have the given FileID.
-static unsigned countFileIDs(ArrayRef<CounterMappingRegion> Regions,
-                             unsigned FileID) {
-  unsigned Result = 0;
-  for (const auto &I : Regions) {
-    if (I.FileID == FileID)
-      ++Result;
-    if (I.FileID > FileID)
-      break;
-  }
-  return Result;
-}
-
 /// \brief Encode the counter.
 ///
 /// The encoding uses the following format:
@@ -142,55 +129,58 @@ void CoverageMappingWriter::write(raw_ostream &OS) {
   // Split the regions into subarrays where each region in a
   // subarray has a fileID which is the index of that subarray.
   unsigned PrevLineStart = 0;
-  unsigned CurrentFileID = MappingRegions.front().FileID;
-  assert(CurrentFileID == 0);
-  encodeULEB128(countFileIDs(MappingRegions, CurrentFileID), OS);
-  for (const auto &I : MappingRegions) {
-    if (I.FileID != CurrentFileID) {
+  unsigned CurrentFileID = ~0U;
+  for (auto I = MappingRegions.begin(), E = MappingRegions.end(); I != E; ++I) {
+    if (I->FileID != CurrentFileID) {
       // Ensure that all file ids have at least one mapping region.
-      assert(I.FileID == (CurrentFileID + 1));
+      assert(I->FileID == (CurrentFileID + 1));
+      // Find the number of regions with this file id.
+      unsigned RegionCount = 1;
+      for (auto J = I + 1; J != E && I->FileID == J->FileID; ++J)
+        ++RegionCount;
       // Start a new region sub-array.
-      CurrentFileID = I.FileID;
-      encodeULEB128(countFileIDs(MappingRegions, CurrentFileID), OS);
+      encodeULEB128(RegionCount, OS);
+
+      CurrentFileID = I->FileID;
       PrevLineStart = 0;
     }
-    Counter Count = Minimizer.adjust(I.Count);
-    switch (I.Kind) {
+    Counter Count = Minimizer.adjust(I->Count);
+    switch (I->Kind) {
     case CounterMappingRegion::CodeRegion:
       writeCounter(MinExpressions, Count, OS);
       break;
     case CounterMappingRegion::ExpansionRegion: {
       assert(Count.isZero());
-      assert(I.ExpandedFileID <=
+      assert(I->ExpandedFileID <=
              (std::numeric_limits<unsigned>::max() >>
               Counter::EncodingCounterTagAndExpansionRegionTagBits));
       // Mark an expansion region with a set bit that follows the counter tag,
       // and pack the expanded file id into the remaining bits.
       unsigned EncodedTagExpandedFileID =
           (1 << Counter::EncodingTagBits) |
-          (I.ExpandedFileID
+          (I->ExpandedFileID
            << Counter::EncodingCounterTagAndExpansionRegionTagBits);
       encodeULEB128(EncodedTagExpandedFileID, OS);
       break;
     }
     case CounterMappingRegion::SkippedRegion:
       assert(Count.isZero());
-      encodeULEB128(unsigned(I.Kind)
+      encodeULEB128(unsigned(I->Kind)
                         << Counter::EncodingCounterTagAndExpansionRegionTagBits,
                     OS);
       break;
     }
-    assert(I.LineStart >= PrevLineStart);
-    encodeULEB128(I.LineStart - PrevLineStart, OS);
+    assert(I->LineStart >= PrevLineStart);
+    encodeULEB128(I->LineStart - PrevLineStart, OS);
     uint64_t CodeBeforeColumnStart =
-        uint64_t(I.HasCodeBefore) |
-        (uint64_t(I.ColumnStart)
+        uint64_t(I->HasCodeBefore) |
+        (uint64_t(I->ColumnStart)
          << CounterMappingRegion::EncodingHasCodeBeforeBits);
     encodeULEB128(CodeBeforeColumnStart, OS);
-    assert(I.LineEnd >= I.LineStart);
-    encodeULEB128(I.LineEnd - I.LineStart, OS);
-    encodeULEB128(I.ColumnEnd, OS);
-    PrevLineStart = I.LineStart;
+    assert(I->LineEnd >= I->LineStart);
+    encodeULEB128(I->LineEnd - I->LineStart, OS);
+    encodeULEB128(I->ColumnEnd, OS);
+    PrevLineStart = I->LineStart;
   }
   // Ensure that all file ids have at least one mapping region.
   assert(CurrentFileID == (VirtualFileMapping.size() - 1));