[llvm-dev] 7-8% compile time slowdowns in LLVM 10

David Chisnall via llvm-dev llvm-dev at lists.llvm.org
Thu Apr 16 05:39:04 PDT 2020

On 15/04/2020 18:32, Alexandre Ganea via llvm-dev wrote:
> I suggested Neil to apply https://reviews.llvm.org/D71786 (rpmalloc) and 
> he reported:
> “[..] its about 6.5% faster using the rpmalloc LLVM vs LLVM 9 without. 
> It is a cool 14% faster than LLVM 10 too!”
> (https://twitter.com/sheredom/status/1250138086811602944?s=20)
> I ran some tests locally, and as a first order of approximation, /even 
> without rpmalloc/ it seems Clang 10 is faster than Clang 9 for a whole 
> build. Although locally when iterating on a single file, it could be 
> slower like Neil suggests.

FWIW: I'm running locally with snmalloc replacing jemalloc as the 
default FreeBSD allocator and clang is about 2% faster in some very 
ad-hoc and informal testing. Over SPEC on Windows I think (from memory, 
testing was a while ago) we see around a 30% speedup of snmalloc vs the 
Windows allocator (which has a lot of security features not present in 
snmalloc).  We've increased the performance of snmalloc since we last 
did a SPEC run, malloc is now 14 instructions with no atomic operations 
in the common case.


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