Sven Barth wrote:
Can the compiler optimise this operation choosing the fastest one -
probably depending on the architecture x86, arm, aso.
It can if someone codes support for it (maybe some code generators
already have such simplifications). I thought I've at least seen such
code for integers (that exactly converts *2 to a shl), but I can't find
it currently...
With the caveat that at least some Pentiums have a limited amount of
shifting hardware (specifically, of the 2x ALUs in a processor only one
has a barrel shifter on the output). That might have the effect that
converting a long run of *2 to <<1 would have the effect of preventing
work being routed to half of the ALUs.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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