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Old 13th February 2020, 00:06   #1  |  Link
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Join Date: Jun 2005
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Older compiler versions produce faster code?

I did a small performance test with a CPU-bound application that I'm currently working on and came to realize that older compiler versions seem to produce much faster code.

If we ignore that MSVC++ seems to fail miserably at generating x86 (32-Bit) code, the latest versions of both, MSVC++ and GCC, produce significantly slower code than the older versions of the same compiler:

Smaller is better. Each binary was measured 8 times, and only the fastest run was kept. Source code and compiler flags (especially things like "-O", "-march" and "-mtune") were the same for all compiler versions.

I know that this is just one specific application, so the results certainly can not be generalized. But any idea what's going on?

Do the latest compiler versions really contain serious performance regressions for this type of application, or did the defaults for some influential compiler settings change between the different compiler versions?

At least GCC has so many options and flags, that I have no idea, whether GCC 9.x can be tweaked to produce code as fast as GCC 5.x...
There was of course no way of knowing whether you were being watched at any given moment.
How often, or on what system, the Thought Police plugged in on any individual wire was guesswork.

Last edited by LoRd_MuldeR; 13th February 2020 at 00:25.
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