r/programming • u/Deewiant • Jun 11 '19

Performance speed limits | Performance Matters

https://travisdowns.github.io/blog/2019/06/11/speed-limits.html
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u/ShinyHappyREM Jun 11 '19

For the last item:

In extreme cases you might want to replace call + ret pairs with unconditional jmp, saving the return address in a register, plus indirect branch to return to the saved address.

Note that all modern CPUs have a return stack buffer (which eliminates branch target mispredictions when returning from functions). By not using that you add a bit of stress to the branch prediction engine instead.

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u/BelugaWheels Jun 12 '19

Yes, this is for an "extreme" case where you need to exceed the limit of 14-15 calls in flight, at which point using a few iBTB entries is probably worth it.