On Mon, May 10, 2021 at 11:11:36AM +0200, Jan Hubicka wrote: > > On Sun, 9 May 2021, Segher Boessenkool wrote: > > > On Sun, May 09, 2021 at 12:54:08AM +0800, Xi Ruoyao via Gcc-help wrote: > > > > On Sat, 2021-05-08 at 20:07 +0800, 172060045@xxxxxxxxxx wrote: > > > > > Recently I noticed that gcc -O2 didn't turn on vectorization > > > > > optimization， > > > > > which it turns on in clang -O2. > > > > > > > > > > Does GCC think it involves the trade-off of space speed, or other > > > > > considerations? > > > > > > -O2 is for optimisations that (almost) never degrade code quality. -O3 > > > is for those that are only beneficial "on average". > > > > In particular -O2 is a balance of compile-time, generated code size > > and resulting performance. Vectorization with the -O2 default > > cost model of "cheap" tends to mostly increase the first and the second > > whilst only moderately affecting the last. > > Last time I ran -O2 with cheap model enabled, the code size was actually > decreasing at average for SPEC which was a bit of a surprise. Huh! Will you investigate how/why this happens? Also, it probably is quite different on different archs. Interesting times ahead. > I plan to re-do the benchmarks soon now gcc11 branched. Great, thanks in advance, gl;hf :-) Segher
