On Fri, Oct 20, 2017 at 9:53 AM, Jakub Jelinek <ja...@redhat.com> wrote: > On Fri, Oct 20, 2017 at 09:48:38AM +0200, Richard Biener wrote: >> How does it work semantically to have different exec charsets? That is, >> if "strings" flow from a region with one -fexec-charset setting to a region >> with another one is that undefined behavior? Do we now require >> external function declarations to be in the proper region (declared under >> the appropriate exec charset flag)? This would mean that passing >> the exec charset in effect as additional argument isn't a possibility. >> >> Or do we have to treat -fexec-charset similar to -frounding-math, that is, >> we can't ever _interpret_ any string in the compiler? [unless -fexec-charset >> is the same everywhere] >> >> I think the -frounding-math route is probably the easiest (and wisest >> given the quite low test coverage we'll get) route. Thus, add a >> -fmixed-charset >> flag and reject any exec-charset attribute/pragma if that flag is not set? >> With LTO we could always add this and/or merge -fexec-charset flags >> appropriately, >> injecting -fmixed-charset in case TUs use different settings. > > It wouldn't have to be an option, simply mark in cfun all functions that > have more than one exec charset and give up on all optimizations/warnings > that require to read the characters and merge that unknown exec_charset > flag during inlining etc. Though, that might still not be enough, e.g. > the whole function might have one exec charset, but a global const char [] > variable might have another one and during optimization we might be looking > at that. So perhaps it would need to be a per-TU flag merged during LTO.
There's also IPA flow of strings between functions so unless mixing exec charsets invokes undefined behavior I can't see how a per-function flag would help. But yes, if we can reliably detect whether multiple exec charsets are used in a TU we can make this a flag that doesn't have to be set by the user. But that means the pragma probably _always_ forces that flag given we have that forced pre-included file on some targest and the pragma token would occur after that... Richard. > Jakub
