CoverageMappingReader behaves O(N^2) slowly with hundreds thousand of Expansions #113173
Description
For example RISCVInstructionSelector.cpp (possibly since #110782):
- NumRegions 892,077
- NumFiles 387,470 (Expansions)
It takes bunch of minutes for me.
llvm-cov is not required for reproduction. Just add -Xclang -dump-coverage-mapping onto -profile-instr-generate -fcoverage-mapping. The dump calls CoverageMappingReader for encoded covmap.