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ae0620c4e9
Introduce -mllvm -sanitizer-coverage-8bit-counters=1 which adds imprecise thread-unfriendly 8-bit coverage counters. The run-time library maps these 8-bit counters to 8-bit bitsets in the same way AFL (http://lcamtuf.coredump.cx/afl/technical_details.txt) does: counter values are divided into 8 ranges and based on the counter value one of the bits in the bitset is set. The AFL ranges are used here: 1, 2, 3, 4-7, 8-15, 16-31, 32-127, 128+. These counters provide a search heuristic for single-threaded coverage-guided fuzzers, we do not expect them to be useful for other purposes. Depending on the value of -fsanitize-coverage=[123] flag, these counters will be added to the function entry blocks (=1), every basic block (=2), or every edge (=3). Use these counters as an optional search heuristic in the Fuzzer library. Add a test where this heuristic is critical. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231166 91177308-0d34-0410-b5e6-96231b3b80d8
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