[fpc-devel] The 15k bounty: Optimizing executable speed for Linux x86 / LLVM

[Jonas Maebe]

On 16/11/18 22:44, Florian Klämpfl wrote:
> With some compiler tuning and a few tricks (two changes to the code and hand-simulated peephole optimizations, but I
> think these tricks can also the compiler do):

You can improve performance further by devirtualising all method calls 
using wpo. First compile it with -FWvipri.wpo -OWDEVIRTCALLS,OPTVMTS and 
next with -Fwvipri.wpo -OwDEVIRTCALLS,OPTVMTS (at least on my machine it 
gives a small boost, and makes the results also more stable).

Since I only have a preliminary llvm version (with Dwarf EH) running on 
macOS, I can't provide a direct Kylix comparison. The versions below are 
both x86-64. As mentioned before, a 32 bit FPC/LLVM is still quite a way 
off.

* FPC 3.0.4 -MDelphi -O2 -Fwvipri.wpo -OwDEVIRTCALLS,OPTVMTS:

$ time ./vipribenchmemcache_nodeps
VipriBenchThreaded - RunningTimeSeconds=5, TestCount=100, StartSeq=0, 
NumberOfChannels=6, BufferPackets=5000, NumberOfSynchroThreads=4
.................................................................................................
Time: 5016ms = 9669059 pkts/s = 14680 MB/s

real	0m5.137s
user	0m5.042s
sys	0m0.017s

FPC 3.3.1 + llvm (clang from Xcode 10.1 with -O3 on FPC-generated llvm 
IR) and -Fwvipri.wpo -OwDEVIRTCALLS,OPTVMTS (no LLVM link-time 
optimization):

$ time ./vipribenchmemcache_nodeps_llvm
VipriBenchThreaded - RunningTimeSeconds=5, TestCount=100, StartSeq=0, 
NumberOfChannels=6, BufferPackets=5000, NumberOfSynchroThreads=4
.................................................................................................................
Time: 5018ms = 11259466 pkts/s = 17094 MB/s

real	0m5.161s
user	0m5.060s
sys	0m0.017s


Jonas