On Fri, Sep 11, 2020 at 03:17:19PM -0500, Qing Zhao wrote: > > On Sep 11, 2020, at 3:05 PM, Segher Boessenkool > > <seg...@kernel.crashing.org> wrote: > > On Fri, Sep 11, 2020 at 02:40:06PM -0500, Qing Zhao wrote: > >>> On Sep 11, 2020, at 12:13 PM, Segher Boessenkool > >>> <seg...@kernel.crashing.org> wrote: > >>> On Fri, Sep 11, 2020 at 11:52:29AM -0500, Qing Zhao wrote: > >>>> I don’t understand why it’s not correct if we clearing call-clobbered > >>>> registers > >>>> AFTER restoring call-preserved registers? > >>> > >>> Because the compiler backend (or the linker! Or the dynamic linker! > >>> Etc.) can use volatile registers for their own purposes. > >> > >> For the following sequence at the end of a routine: > >> > >> *...* > >> “restore call-preserved registers” > >> *clear call-clobbered registers"* > >> *ret* > >> > >> “Clear call-clobbered registers” will only clear the call-clobbered > >> registers that are not live at the end of the routine. > > > > And they can be written again right after the routine, by linker- > > generated code for example. This is a waste. > > > >> In the new version of the patch, the implementation of clearing > >> call-clobbered registers is done in backend, middle end only > >> computes a hard register set based on user option, source attribute, data > >> flow information, and function abi information, and > >> Then pass this hard register set to the target hook to generate the > >> clearing sequence. The backend will have all the details > >> on the special situations you mentioned. > >> > >> Let me know any more concerns here. > > > > I cannot find that patch? > > Haven’t finished yet. -:).
Ah okay :-) If you have, please send it in a new thread (not as a reply)? So that it will be much easirer to handle :-) Segher
