Hello, On Sat, 1 Jun 2024, Richard Biener via Gcc wrote:
> >>> You have a pointer how to define a target optab? I looked into optabs > >>> code but found no appropriate hook. For isinf<mode> is seems is is > >>> enough to provide a failing expander, but other functions like isnan > >>> don't have an optab entry, so there is a hook mechanism to extend optabs? > >> Just add corresponding optabs for the missing cases (some additions are > >> pending, like isnornal). There’s no hook to prevent folding to FP > >> compares nor is that guarded by other means (like availability of native > >> FP ops). Changing the guards would be another reasonable option. > >> Richard > > > > There are many other such folds, e.g. for isdigit(). The AVR libraries > > have all this in hand-optimized assembly, and all these built-in expansions > > are bypassing that. Open-coded C will never beat that assemlbly code, at > > least not with the current GCC capabilities. > > The idea is that isdigit() || isalpha() or similar optimize without > special casing the builtins. > > > How would I go about disabling / bypassing non-const folds from ctype.h and > > the many others? > > I think this mostly shows we lack late recognition of open-coded isdigit > and friends, at least for the targets where inlining them is not > profitable. > > A pragmatic solution might be a new target hook, indicating a specified > builtin is not to be folded into an open-coded form. Well, that's what the mechanism behind -fno-builtin-foobar is supposed to be IMHO. Hopefully the newly added additional mechanism using optabs and ifns (instead of builtins) heeds it. > A good solution would base this on (size) costs, the perfect solution > would re-discover the builtins late and undo inlining that didn’t turn > out to enable further simplification. > > How is inlined isdigit bad on AVR? Is a call really that cheap > considering possible register spilling around it? On AVR with needing to use 8bit registers to do everything? I'm pretty sure the call is cheaper, yeah :) Ciao, Michael.
