I am using OpenSSL 1.1.1 11 Sep 2018

In file https://github.com/openssl/openssl/blob/ed086e2/crypto/bn/asm/x86_64-mont5.pl#L65

The regexpr used to match the compiler version string expects a single digit before the first dot.
This is problematic because clang master (as well as the next clang release) is clang version 10.0.0.
So there are two digits before the first dot.

On targets that support ADX, a more optimal call to __bn_sqrx8x_reduction is generated (instead of a call to __bn_sqr8x_reduction which doesn't use MULX/ADCX/ADOX).
The calls to the hand written assembly variant that uses ADX instructions (i.e. __bn_sqrx8x_reduction) is only emitted if variable $addx is set. Otherwise, the code falls back to the less optimal __bn_sqr8x_reduction.

regexpr:

/((?:^clang|LLVM) version|.*based on LLVM) ([3-9])\.([0-9]+)/)

works fine with clang 9 because there is a single digit before the dot.
It fails on clang master (clang version 10.0.0 (https://github.com/llvm/llvm-project.git ce8795eb6c054328173876fe3fb126fd0b0b8aba))
It will start failing on the clang 10 release as soon as the branch is created.

Verified with clang master when building for znver1 (-march=znver1) which supports ADX.

This issue was originally filed against clang here: https://bugs.llvm.org/show_bug.cgi?id=44409
as a consequence of a 24% perf regression in OpenSSL reported by Phoronix here: https://www.phoronix.com/scan.php?page=article&item=gcc-clang-3960x&num=6

I was able to fix the issue and fully recover the lost performance by replacing the problematic regexpr with this one:

/((?:^clang|LLVM) version|.*based on LLVM) ([0-9]+)\.([0-9]+)/)

Thanks
-Andrea