On Thu, Nov 1, 2012 at 4:07 PM, Xinliang David Li <davi...@google.com> wrote: > On Thu, Nov 1, 2012 at 3:57 PM, Ian Lance Taylor <i...@google.com> wrote: >> On Thu, Nov 1, 2012 at 10:00 AM, Dehao Chen <de...@google.com> wrote: >>> >>> I see your point. How about we guard these changes with a flag, say >>> -gless-jumpy, so that people can always choose between better coverage >>> and less jumpy gdb behavior (it's also important for some other >>> clients like AutoFDO). I will have a series of patches to follow soon >>> that can be guarded by this flag. >> >> This feels to me like an attempt to address the problem in the wrong >> place. It seems to me that it would be better to do one of: >> >> * Use -Og and ensure that -Og does not move the code around. >> Presumably this would lead to worse runtime performance and better >> performance in the debugger. >> >> * Add heuristics to the debugger to jump around less. >> >> * Add a new debug facility to mark the statement as attached to a >> particular source location, but moved relative to other source >> locations. Add facilities to the debugger to take that into account. >> >> That said, I suppose I can imagine a mode like you suggest. It >> shouldn't be a -g option, it should be a -f option, like >> -fdiscard-moved-insn-debug-locations or something. That would be >> along the lines of -fno-var-tracking: we generate worse debug info >> upon user request.
I don't see why debug info would be worse if we add something like -fdiscard-moved-insn-debug-locations, as long as it is not turned on by default. Any thoughts? >> > > Or have a common umbrella option to guard all changes that improves DOC. Is it like -Og approach as Ian mentioned? Yes, we can sacrifice some performance (maybe 5%?) to get more accurate source level profile. But if we plan to use AutoFDOed binary to collect AutoFDO profile, it'll suffer the same debug problem again... Thanks, Dehao > > David > > > >> Ian
