https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94781
--- Comment #5 from ishikawa,chiaki <ishikawa at yk dot rim.or.jp> --- Thank you for your comment. (In reply to Richard Biener from comment #4) > The time-report you attached is mostly flat and I don't see anything > eye-popping pointing at a regression. With -O0 my GCC9 is faster (well, > noise). I was concerned with the ELAPSED time, and I notice that, in my testing, "phase last asm" of v9 and v8 spent a tad long time than v7. v9 phase last asm : 6.03 ( 5%) 0.24 ( 2%) 19.07 ( 12%) 127204 kB ( 2%) v8 phase last asm : 5.62 ( 4%) 0.24 ( 2%) 15.43 ( 10%) 103215 kB ( 2%) v7 phase last asm : 4.03 ( 3%) usr 0.16 ( 1%) sys 6.51 ( 5%) wall 101000 kB ( 2%) ggc v9 spends more than 12 seconds and v8 spends about 9 seconds longer than v7. But I am not sure what this "phase last asm" does and why it spends more ELAPSED time in v9 and v8 than in v7. > Confirmed for -O2: > > > /usr/bin/time /space/rguenther/install/gcc-7.5/bin/g++ -S > > UnifiedBindings23-v7.cpp -std=gnu++1z -w -O2 > 112.50user 1.83system 2:01.65elapsed 93%CPU (0avgtext+0avgdata > 2732664maxresident)k > 1952inputs+36528outputs (6major+678054minor)pagefaults 0swaps > > /usr/bin/time /space/rguenther/install/gcc-8.4/bin/g++ -S > > UnifiedBindings23-v7.cpp -std=gnu++1z -w -O2 > 83.44user 1.27system 1:26.34elapsed 98%CPU (0avgtext+0avgdata > 2789396maxresident)k > 48640inputs+41088outputs (62major+687702minor)pagefaults 0swaps > > /usr/bin/time /space/rguenther/install/gcc-9.3/bin/g++ -S > > UnifiedBindings23-v7.cpp -std=gnu++1z -w -O2 > 128.28user 1.90system 2:19.51elapsed 93%CPU (0avgtext+0avgdata > 2695708maxresident)k > > Note how my GCC 8 build is significantly faster than GCC 7! Hmm... Did you use special flag to create your compiler? I am using AMD Ryzen 7 1700 eight core CPU (my linux runs inside VirtualBox image under Windows 10 and it is assigned 7 virtual CPU core.). Maybe I need to build my own G++ compiler tuned for AMD Ryzen 7 if you used a special compiler flags when you built your V8 and V9 compiler because the elapsed time difference between v7 and v9 is rather smallish in comparison to the difference I observed on my PC (module the option difference.) > > note that this kind of regression can easily happen because we generate > more code because of some different optimization decisions. For example > the GCC 8 generated object is > > > size UnifiedBindings23-v7.o > text data bss dec hex filename > 2502864 10136 37392 2550392 26ea78 UnifiedBindings23-v7.o > > while GCC 9 generates > > > size UnifiedBindings23-v7.o > text data bss dec hex filename > 2788944 16488 37392 2842824 2b60c8 UnifiedBindings23-v7.o > > I realize I didn't use the full set of options you did (in particular I > omitted > -g). The few extra options I needed to omit for v7 and v8 might explain the slow down. I will check for this by removing the options from v9 compilation as well. > My tests also seem noisy (machine isn't idle, 2nd run of the GCC 9 > compile > dialed in at 100s) I bet you are using very fast CPU :-)
