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re: Advantages of 64-bit vs 32-bit on old hardware
Oh, and -Os is probably a bad idea if you want performance compared to
say -O2. Layout of instructions in the I$ is important for efficient
instruction issue on USI and USII cpus. Ideally you want 2 integer ops
followed by 1 load/store and 1 branch or FP op to get optimal performance.
Breaking this group across cache lines will require an extra cycle. And
being a superscalar, speculation is good for performance but bad for
code size. I don't think you're making the right tradeoff here.
it's actually quite common for -Os to beat -O2 in many benchmarks,
simply because it is -O2 + a bit more. i believe some people /
projects use -Os by default.
but i completely agree that anyone who cares about performance
actually needs to test and compare speeds to really know what
works for their application.
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