[Bug tree-optimization/88760] GCC unrolling is suboptimal

rearnsha at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Fri Sep 27 12:33:00 GMT 2019


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88760

--- Comment #25 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Well very small loops should be unrolled more than slightly larger ones.  So
perhaps if the loop body is only 3 or 4 instructions it should be unrolled four
times but above that perhaps only twice.

Some consideration should be given, however, to whether the target
micro-architecture has looping buffers as unrolling beyond the limit of such
structures will hurt performance.


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