Back 20 or more years ago I used to do a lot of rec math competition programming and found that the metrowerks c++ compiler made massively faster programs than gcc, vsstudio, intel and everything else I tried then.

This seemed to be simply down to variable alignment; the programs took more memory but ran much faster, particularly multi-core (which was still high end then).

And this was on x86 where metrowerks weren't really competing, and was probably accidental. But the programs it compiled were fast.

I'd be surprised if anyone even knew that metrowerks had a c++ compiler on x86 on windows. At the time metrowerks were on the tail end of their domination of mac compilers from before mac ran on x86.