Unverified Commit 0135cf99 authored by Fangrui Song's avatar Fangrui Song Committed by GitHub
Browse files

[Coverage] Fix quadratic propagation in RawCoverageMappingReader (#194996) 

```
llvm-cov export /tmp/Cov/bin/lld -instr-profile=/tmp/Cov/cov.profdata -format=lcov --sources lld/ELF/Arch/RISCV.cpp
```
does not finish after minutes.

Root cause: The expansion-region count propagation loop is bounded by
`VirtualFileMapping.size()`, the number of macro expansions.

In the TableGen-generated `RISCVGenDAGISel.inc` (depended on by
LLVMLTO), `NumFileMappings` is 74941 (largely due to the `TARGET_VAL`
macro). With 149887 mapping regions, the loop does not finish after more
than ten minutes.

Fix with an early break.
parent e3533648

llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp

+13 −6
Original line number Diff line number Diff line
@@ -440,24 +440,31 @@ Error RawCoverageMappingReader::read() { 
  // Set the counters for the expansion regions.

  // i.e. Counter of expansion region = counter of the first region

  // from the expanded file.

  // Perform multiple passes to correctly propagate the counters through

  // all the nested expansion regions.

  // Perform multiple passes to correctly propagate the counters through all the

  // nested expansion regions. Iterate until no count changes.

  SmallVector<CounterMappingRegion *, 8> FileIDExpansionRegionMapping;

  FileIDExpansionRegionMapping.resize(VirtualFileMapping.size(), nullptr);

  for (unsigned Pass = 1, S = VirtualFileMapping.size(); Pass < S; ++Pass) {

  for (;;) {

    for (auto &R : MappingRegions) {

      if (R.Kind != CounterMappingRegion::ExpansionRegion)

        continue;

      assert(!FileIDExpansionRegionMapping[R.ExpandedFileID]);

      FileIDExpansionRegionMapping[R.ExpandedFileID] = &R;

    }

    bool Changed = false;

    for (auto &R : MappingRegions) {

      if (FileIDExpansionRegionMapping[R.FileID]) {

        FileIDExpansionRegionMapping[R.FileID]->Count = R.Count;

        FileIDExpansionRegionMapping[R.FileID] = nullptr;

      auto *&Slot = FileIDExpansionRegionMapping[R.FileID];

      if (Slot) {

        if (Slot->Count != R.Count) {

          Slot->Count = R.Count;

          Changed = true;

        }

        Slot = nullptr;

      }

    }

    if (!Changed)

      break;

  }



  return Error::success();

}