Hi! On Tue, Jan 08, 2019 at 12:03:06PM +0000, Richard Sandiford wrote: > Bernd Edlinger <bernd.edlin...@hotmail.de> writes: > > Meanwhile I found out, that the stack clobber has only been ignored up to > > gcc-5 (at least with lra targets, not really sure about reload targets). > > From gcc-6 on, with the exception of PR arm/77904 which was a regression due > > to the underlying lra change, but fixed later, and back-ported to gcc-6.3.0, > > this works for all targets I tried so far. > > > > To me, it starts to look like a rather unique and useful feature, that I > > would > > like to keep working. > > Not sure what you mean by "unique". But forcing a frame is a bit of > a slippery concept. Force it where? For the asm only, or the whole > function? This depends on optimisation and hasn't been consistent > across GCC versions, since it depends on the shrink-wrapping > optimisation. (There was a similar controversy a while ago about > to what extent -fno-omit-frame-pointer should "force a frame".)
It's not forcing a frame currently: it's just setting frame_pointer_needed. Whatever happens from that is the target's business. > The effect on the redzone seems like something that should be specified > explicitly rather than as an (accidental?) side effect of listing the > sp in the clobber list. Maybe this would be another use for the "asm > attributes" proposal. "noreturn" was another attribute suggested on > IRC yesterday. Redzone is target-dependent. "noreturn"... What would that mean, *exactly*? It cannot execute any code the compiler can see, so such asm is better off as real asm anyway (not inline asm). > But either way, the general feeling seems to be that going straight to a > hard error is too harsh, since there's quite a bit of existing code that > has the clobber. This patch implements the compromise discussed on IRC > yesterday of making it a -Wdeprecated warning instead. The patch looks fine to me. Thanks! Segher
