Erik Desjardins 87d02e0dfd Recommit "[Support] change StringMap hash function from djbHash to xxHash" ...

This reverts commit 37eb9d13f8.

Test failures have been fixed:

- ubsan failure fixed by 72eac42f21
- warn-unsafe-buffer-usage-fixits-local-var-span.cpp fixed by
  03cc52dfd1 (wasn't related)
- test-output-format.ll failure was spurious, build failed at
  https://lab.llvm.org/buildbot/#/builders/54/builds/3545 (b4431b2d94)
  but passed at
  https://lab.llvm.org/buildbot/#/builders/54/builds/3546 (5ae99be037)
  which is before my revert
  b4431b2d94...5ae99be037

Original commit message:

    Depends on https://reviews.llvm.org/D142861.

    Alternative to https://reviews.llvm.org/D137601.

    xxHash is much faster than djbHash. This makes a simple Rust test case with a large constant string 10% faster to compile.

    Previous attempts at changing this hash function (e.g. https://reviews.llvm.org/D97396) had to be reverted due to breaking tests that depended on iteration order.
    No additional tests fail with this patch compared to `main` when running `check-all` with `-DLLVM_ENABLE_PROJECTS="all"` (on a Linux host), so I hope I found everything that needs to be changed.

    Differential Revision: https://reviews.llvm.org/D142862

2023-02-19 16:52:26 -05:00

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