On December 20, 2019 1:41:19 AM GMT+01:00, Jeff Law <l...@redhat.com> wrote: >On Thu, 2019-12-19 at 17:06 -0600, Qing Zhao wrote: >> Hi, Dmitry, >> >> Thanks for the responds. >> >> Yes, routine size only cannot determine the complexity of the >routine. Different compiler analysis might have different formula with >multiple parameters to compute its complexity. >> >> However, the common issue is: when the complexity of a specific >routine for a specific compiler analysis exceeds a threshold, the >compiler might consume all the available memory and abort the >compilation. >> >> Therefore, in order to avoid the failed compilation due to out of >memory, some compilers might set a threshold for the complexity of a >specific compiler analysis (for example, the more aggressive data flow >analysis), when the threshold is met, the specific aggressive analysis >will be turned off for this specific routine. Or the optimization level >will be lowered for the specific routine (and given a warning during >compilation time for such adjustment). >> >> I am wondering whether GCC has such capability? Or any option >provided to increase or decrease the threshold for some of the common >analysis (for example, data flow)? >> >There are various places where if we hit a limit, then we throttle >optimization. But it's not done consistently or pervasively. > >Those limits are typically around things like CFG complexity.
Note we also have (not consistently used) -Wmissed-optimizations which is supposed to warn when we run into this kind of limiting telling the user which knob he might be able to tune. Richard. >We do _not_ try to recover after an out of memory error, or anything >like that. > >jeff >>
