On Thu, Nov 1, 2012 at 4:16 PM, Dehao Chen <de...@google.com> wrote: > 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...
No not the same as -Og -- DOC means debugging for fully optimized code. David > > Thanks, > Dehao > >> >> David >> >> >> >>> Ian
