[all-commits] [llvm/llvm-project] b1048f: [libFuzzer] Preserve position hint in auto dictionary

[Fabian Meumertzheim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b1048ff68298c1c4e303bbb77ca1832b2f873cd6
      https://github.com/llvm/llvm-project/commit/b1048ff68298c1c4e303bbb77ca1832b2f873cd6
  Author: Fabian Meumertzheim <meumertzheim at code-intelligence.com>
  Date:   2021-05-04 (Tue, 04 May 2021)

  Changed paths:
    M compiler-rt/lib/fuzzer/FuzzerMutate.cpp

  Log Message:
  -----------
  [libFuzzer] Preserve position hint in auto dictionary

Currently, the position hint of an entry in the persistent auto
dictionary is fixed to 1. As a consequence, with a 50% chance, the entry
is applied right after the first byte of the input. As the position 1
does not appear to have any particular significance, this is likely a
bug that may have been caused by confusing the constructor parameter
with a success count.

This commit resolves the issue by preserving any existing position hint
or disabling the hint if the original entry didn't have one.

Reviewed By: morehouse

Differential Revision: https://reviews.llvm.org/D101686