On 10/3/18 11:04 AM, Jan Hubicka wrote: >> >> That was promised to be done by Honza Hubička. He's very skilled in IPA optimizations and he's aware >> of optimizations that cause troubles for live-patching. > > :) I am not sure how skilful I am, but here is what I arrived to. Heh! Thanks for the analysis. > > We have transformations that are modeled as clonning, which are > - inlining (can't be disabled completely because of always inline, but -fno-inline > does most of stuff) > - cloning (disabled via -fno-ipa-cp) > - ipa-sra (-fno-ipa-sra) > - splitting (-fno-partial-inlining) > These should play well with Martin's tracking code I hope so! > > We propagate info about side effects of function: > - function attribute discovery (pure, const, nothrow, malloc) > Some of this can be disabled by -fno-ipa-pure-const, but not all > of it. Would it be possible to add option for the remaining ones? Nothrow does not have flag but it is obviously not a concern > for C++ s/C++/C? > - ipa-pta (disabled by default, -fno-ipa-pta) > - ipa-reference (list of accessed/modified global vars), disable by -fno-ipa-refernece > - stack alignment requirements (no flag to disable) Would it be possible to add flag for it? Can you please point to a location where the optimization happen? > - inter-procedural register allocation (-fno-ipa-ra) > > We perform discovery of functions/variables with no address taken and > optimizations that are not valid otherwise such as duplicating them > or doing skipping them for alias analysis (no flag to disable) Can you be please more verbose here? What optimizations do you mean? > > Identical code folding merges function bodies that are semanticaly equivalent > and thus one can't patch one without patching another, -fno-ipa-icf Agree, I recommend disabling that. > > Unreachable code/variable removal may be concern too (no flag to disable) For functions that should be fine and handled by my script. For variables can be problem when a variable becomes alive But that should be extremely rare for live-patching. > > Write only global variable discovery (no flag to dosable) Similarly. > > Visibility changes with -flto and/or -fwhole-program > > We also have profile propagation (discovery of cuntions used only in cold regions, > but that I guess is only performance issue not correctness) > No flag to disable Hope these 2 does not happen for current Linux kernel. Martin > > Honza > >> >> Martin >> >>> >>> thanks. >>> >>> Qing >>> >>
