On Thu, Nov 18, 2010 at 3:58 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >> Some text size measurement. >> >> Summary: >> 1) LTO with -O3 bloats up code considerably; > Yes, you need either -fwhole-program or -fuse-linker-plugin to make it behave > sanely. > > For Mozilla I have best experience with -fuse-linker-plugin --param > inline-unit-growth=5 That gives me about 16% code size savings (so LTO -O3 is > same size as -Os). This means that it is smaller than > -O2+LTO+-fwhole-program. > >> 2) LTO with -O2 reduces text size compared with -O2 > > An more so with -fwhole-program as you noticed ;)
Actually all the LTO experiments were done with -fwhole-program. > >> 3) Google 4.4.3 based compiler is really effective in reducing C++ >> program size -- this is where the focus of the tuning was done. >> Witnessed by eon in SPEC2k and all C++ apps in SPEC06 > > Again, I would be very interested to see the patches (and sooner than later > given tham I am re-tunning inliner for 4.6 now). Looking at Mozilla I also > concluded that we have a lot of room for improvement. How old is the tree you > use for testing? I recently improved code size somewhat at mainline. > yes -- it may take a while as the code base for our tuning is 4.4.3. >> >> SPEC06 C++ program Data (the first data column is the TOT O2 base number) >> >> 1. TOT O3 vs TOT O2 ( 3.35% total increase) >> >> 471.omnetpp/ 853708 867988 1.67% >> 450.soplex/ 643273 656349 2.03% >> 483.xalancbmk/ 3634416 3777600 3.94% >> 444.namd/ 393142 402038 2.26% >> 473.astar/ 102182 111038 8.67% >> size_sum 5626721 5815013 3.35% >> >> 2. TOT LTO+whole program + O3 vs TOT O2 (0.35% total increase) >> >> 471.omnetpp/ 853708 937728 9.84% >> 450.soplex/ 643273 654057 1.68% >> 483.xalancbmk/ 3634416 3540646 -2.58% >> 444.namd/ 393142 401318 2.08% >> 473.astar/ 102182 112538 10.13% >> size_sum 5626721 5646287 0.35% >> >> 3. TOT LTO+whole program + O2 vs TOT O2 (8.10% total reduction) >> >> 471.omnetpp/ 853708 822868 -3.61% >> 450.soplex/ 643273 611653 -4.92% >> 483.xalancbmk/ 3634416 3245157 -10.71% >> 444.namd/ 393142 391698 -0.37% >> 473.astar/ 102182 99586 -2.54% >> size_sum 5626721 5170962 -8.10% >> >> 4. google 4.4.3 compiler O2 vs TOT O2 (13.95% total reduction) >> >> 471.omnetpp/ 853708 545840 -36.06% >> 450.soplex/ 643273 374674 -41.76% >> 483.xalancbmk/ 3634416 3556306 -2.15% >> 444.namd/ 393142 329897 -16.09% >> 473.astar/ 102182 35301 -65.45% >> size_sum 5626721 4842018 -13.95% > > Hmm, this really seems interesting. Why the changes was not contributed this > stage1? > As you can see, the savings are mainly for C++, and may hurt C -- there are more work needed to make it suitable upstream. Thanks, David > Honza >
