[llvm-branch-commits] compiler-rt: Introduce runtime functions for emulated PAC. (PR #133530)

[Peter Collingbourne via llvm-branch-commits]

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@@ -0,0 +1,7343 @@
+/*
+ * xxHash - Extremely Fast Hash algorithm
+ * Header File
+ * Copyright (C) 2012-2023 Yann Collet
+ *
+ * BSD 2-Clause License (https://www.opensource.org/licenses/bsd-license.php)
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pcc wrote:

Okay, I will contact board at llvm.org about this new usage.

I don't have a strong opinion about the hash algorithm. XXH3_64 was chosen for these reasons:
1. It was the easiest to incorporate into compiler-rt as it was already available as a header-only library without dependencies.
2. It was already being used in LLVM, so I imagined that licensing wouldn't be as much of a concern.
3. It was faster than the other algorithms according to the [xxhash homepage](https://xxhash.com/). BLAKE3 isn't listed there but we can extrapolate from [BLAKE3's claim](https://github.com/BLAKE3-team/BLAKE3) of being ~7x faster than BLAKE2. (I know I said elsewhere that performance is less of a concern for these functions, but all other things being equal, we may as well go with the algorithm with the best performance.)

If the board decides not to allow use in compiler-rt it should be possible to switch to one of the other algorithms after changing its code as needed to remove dependencies.

https://github.com/llvm/llvm-project/pull/133530