On Tue, Nov 19, 2024 at 11:56 AM Kamil Belter via Gcc <gcc@gcc.gnu.org> wrote: > > Hello, > > I would like to set branch prediction based on .gcda files (I know I > could have it automatically with -fprofile-use, but with my specific > use case I can't do it). > > I've tried to use gcov-dump but I can't find any spec how to interpret > this output.
The info doesn't represent a profile but just counter data - you have to reconstruct a profile from that. > I've also tried to use -fprofile-use with -fdump-rtl-all, > -fdump-tree-all, -fdump-ipa-all, -fopt-info and > -ftree-vectorizer-verbose=n flags and see GCC debug output You probably want to restrict that to -fdump-ipa-profile which is the point where the .gcda files are read and applied in a -fprofile-use build. > I got ~200 > new debug files per source file. I see that some of the files contain > some format of source code. Some conditions are marked with percentage > values, for example: > > if (_11 != 0) > goto <bb 1>; [27.00%] > else > goto <bb 2>; [73.00%] > > <bb 1> [local count: 51244186]: > > I'm guessing that this is prediction, but I found in doc that GCC uses > its own heuristics for branch prediction. How to be sure if I'm > looking at predictions from gcda files? Internally we know which counts were based on feedback and which not but I don't think we dump that info. Richard. > And side question what does > "local count" mean? If this is relevant information I'm working with > ARM. > > I would very appreciate your help with my questions. > > Best regards, > Kamil Belter
