[Bug tree-optimization/67153] [5/6 Regression] integer optimizations 53% slower than std::bitset<>

ncm at cantrip dot org gcc-bugzilla@gcc.gnu.org
Mon Aug 10 11:31:00 GMT 2015


--- Comment #4 from ncm at cantrip dot org ---
Also fails 5.2.1 (Debian 5.2.1--15) 5.2.1 20150808
As noted, the third version of the program, using bitset but not using
lambdas, is as slow as the version using unsigned int -- even when built
using gcc-4.9.  (Recall the int version and the first bitset version
run fast when built with gcc-4.9.)

Confirmed that on Westmere, compiled -march=native, all versions 
run about the same speed with all versions of the compiler reported,
and this runtime is about the same as the slow Haswell speed despite
the very different clock rate.

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