[cfe-dev] [llvm-dev] llvm and clang are getting slower

Daniel Berenyi via cfe-dev cfe-dev at lists.llvm.org
Wed Mar 9 00:33:15 PST 2016

Dear All,

One bit got my attention in this discussion:
"if an optimization increases compile time by 5% or increases code size by
5% for a particular benchmark, that benchmark should also be one which sees
a 5% runtime improvement"

In some cases (e.g. distributed scientific computing but I could name a few
more) we'd be happy to trade 2-4 times more compile time to 5% runtime,
because the compile time is on the order of minutes-10 minutes but the
runtime is measured in days-weeks-months. If you multiply that up by the
number of cores in the cluster (tens, hundreds, ...), it boils down to
potentially wasting time and electricity (money and money).

So, for us, we'd be glad to have a switch that enables even the more
expensive optimization passes, basically expressing the following:
"Dear compiler, I give you all the resources you may need, just optimize
whatever you can in this code as much as you can".

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