[fpc-devel] Sorry for poor testing

Martok listbox at martoks-place.de
Tue Jan 15 18:27:54 CET 2019

Am 14.01.2019 um 15:01 schrieb J. Gareth Moreton:
> Martok mentioned doing some checks differently in the bug report in question,
> such as 6 comparisons being faster than a jump table.  Are there any others
> worth mentioning?
Not neccessarily faster, but in that code definitely smaller. Is there a way to
directly estimate how large the generated code might be, maybe something like

For the "faster" question, the cache line occupation matters more than
instruction throughput. If your jumptable gets large enough to force a full data
cache line flush, you could have done a lot of instructions in the time the CPU
waits for the data. And I haven't found reliable information how the
Spectre-related microcode updates changed that, given that both cmp/jmp and
jmp[indirect] used to be heavily optimized, but were both affected.


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