Martin Frb via fpc-devel <fpc-devel@lists.freepascal.org> schrieb am Mo., 29. Sep. 2025, 14:58:
> On 29/09/2025 14:17, Sven Barth via fpc-devel wrote: > > Martin Frb via fpc-devel <fpc-devel@lists.freepascal.org> schrieb am Mo., > 29. Sep. 2025, 12:30: > >> Tested with 3.3.1 d3ac07ad27 >> -O4 >> Win 64 bit >> >> In the code below, compiled with -alr >> .section .text.n_p$project1_$$_foo,"ax" >> .... >> # Var a located in register rbx >> (and it stays in rbx, until the call to write is prepared) >> >> >> >> But if I comment out the "write", and uncomment the "a.w" >> # Var a located at rsp+32, size=OS_64 >> >> Even the initial 2 lines will then NOT use a register for "a"? >> > > The Self parameter of a type helper is a pointer, so the compiler needs to > be able to take the address which in turn prohibits the use of the regvar > optimization for that variable. > > > Ok, I see (well mostly....) > > Does that need to affect (all the) code in which the pointer is used as > just a pointer? > > I mean, ok, (if) for the last statement (where the type helper is called) > it needs to be on the stackframe, then the variable could be stored then. > (and there after) > > But for section of the code where it isn't using the type helper, a copy > could be in a register? => afaik if there are more vars than registers, > then one register can be used for more than one var, just in different > places? So then vars are swapped between frame and register? > > > Well, ok, the type helper could store a copy of self (pointer to the > pointer) somewhere, and that could be accessed. > But then > - any code before the first call to the type helper should be safe to > optimize > - code after would be tricky, as anything could be that copied pointer > (maybe when "pure" functions exists, and the type helper method is pure) > In theory that would be possible, but currently the compiler doesn't keep track *when* an address is taken, only *that* it is. > It also raises the question (I could test that, but...) what happens if I > take a pointer of any other local var => will the compiler see that, and > prevent such a local var from being optimised to a register? > As soon as the address is taken it won't be put into a register anymore as the compiler can't control/track what is done with that address. For example that would also be the case if you'd pass a single element to an open array parameter as then it's passed as a pointer as well (plus a high parameter of 0). Regards, Sven >
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