On 09/11/15 09:57, Richard Earnshaw wrote: > On 07/11/15 09:23, Segher Boessenkool wrote: >> On Fri, Nov 06, 2015 at 11:50:40PM -0800, David Wohlferd wrote: >>>> The same goes for some constraints and almost all output modifiers. >>> >>> Are you suggesting more doc changes? Looking thru the pages you reference: >>> >>> - Starting with 'modifiers', "=+&" and (reluctantly) "%" seem reasonable >>> for inline asm. But both "#*" seem sketchy. >> >> Output modifiers, not constraint modifiers -- things like "%X0" in >> the output template. Many are only useful in the machine description, >> but some (like that 'X' for rs6000) are vital for asm as well. >> > > They're not just useful, they're essential on AArch64 and ARM. They're > needed, for example, to get the 32/64-bit register sizing correct. >
On the other hand, we have %S on ARM which cannot ever be used from inline assembler: it matches the result of a match_operator rule with complex internal structure that could never be generated from user code. > R. > >>> - Under 'simple constraints', "mringX" all (more or less) make sense to >>> me. But "oV<>sp" are not things I can envision using. >> >> Some are more useful on some targets than on others, sure. But these >> generic constraints are extremely unlikely to ever get a change; this >> is not true for target constraints. If we want to delete (or change >> semantics of) some target constraint, and that constraint is documented, >> we have to fear the ire of the one or two users of that constraint. >> >>> - The 'machine constraints' for i386 (the only machine I know) all seem >>> reasonable. However for platforms that support autoincrement >>> (powerpc?), apparently using "m" needs more docs (per >>> https://gcc.gnu.org/ml/gcc/2008-03/msg01079.html). >> >> I think the manual (the "Simple Constraints" section) does describe it >> all, but it could be clearer. The PowerPC 'm' description does a good >> job of explaining things further (for that target). >> >>> Are these the things to which you are referring? I've always assumed >>> the parts that seem obscure here were due to my i386-centric view of the >>> world. Are some of them actually md-only? >> >> Almost everything can be used in asm as well, but many constraints etc. >> are much less useful there. >> >>> There are other minor changes I'd make on some of these pages. But >>> mostly they are not worth it unless I'm doing something else there too. >>> So if there's something here you think needs changing, let me know and >>> I'll take a crack at it. >>> >>> Other than that, I'll keep working my way thru the doc issues in the >>> inline-asm bugs. I've done what I can for 10396. >> >> Thanks again :-) >> >> >> Segher >> >
