> -----Original Message----- > From: Ulrich Weigand [mailto:uweig...@de.ibm.com] > Sent: 17 December 2010 18:48 > To: Bingfeng Mei > Cc: i...@google.com; gcc@gcc.gnu.org; gcc-patc...@gcc.gnu.org > Subject: Re: Is eliminate_regs_in_insn allowed to generate invalid > instruction? > > Bingfeng Mei wrote: > > > I think I found the cause. find_reloads_address returns 0 even > > it reloads both parts of address (see the patch). Therefore, > > corresponding address_reloaded[i] is not set and in > > the following code of find_reloads, > > > > if (EXTRA_CONSTRAINT_STR (operand, c, p)) > > win = 1; > > /* If the address was already reloaded, > > we win as well. */ > > else if (MEM_P (operand) > > && address_reloaded[i] == 1) <-- address_reloaded[i] still > 0 > > win = 1; > > ... > > > > Extra reload is thus generated even it is unnecessary > > and causes ICE. > > As Ian said, since the address wasn't *completely* reloaded (so that > after reload we'll have just a plain base register), it is correct > that address_reloaded must be 0. > > However, if you're running into problems in this part of the code, you > may probably hit another of the long-standing warts in reload: at this > point, you have an address that reload has already decided to reload > certain parts of, and the result has to match one of your port's > extra memory constraints. However, reload at this point has not > actually made any modifications to the address in its RTL form, it > has just recorded in its own tables that *later*, it *will* replace > some subexpressions of that RTL with registers. > > This means that the RTL that is passed to your EXTRA_CONSTRAINT_STR > implementation will still be the *original* un-reloaded address. > And most likely, your back-end will then reject this address as > not valid for your machine. >
Thanks, that is exactly what I see. But is only EXTRA_CONSTRAINT_STR that suffers this issue? It sounds that normal memory constraint should have this problem too. > The way some ports take around this issue is to recognize, in your > EXTRA_CONSTRAINT_STR implementation, certain forms of complex > addresses as those which you *know* reload will already have marked > for reloading, and therefore *accept* them (if they'd otherwise > match the constraint). > > Bye, > Ulrich > > -- > Dr. Ulrich Weigand > GNU Toolchain for Linux on System z and Cell BE > ulrich.weig...@de.ibm.com Bingfeng
