Back end question.

Fri Apr 29 17:17:00 GMT 2011

Hello Ian.
I have one more question. If I have, for example, a define_insn rtx which matches a pattern generated by previous define_expand rtx. define_expand and define_split combination produces either a simple "set" rtx or "set" plus clobber of CC reg. And if in define_insn I specify a constraint that requires such an operand type which should generate a CC clobber, but initially there could be a combination of operands that does not clobber a CC and also does not satisfy constraints, so compiler must reload one or two operands in appropriate registers which satisfies constraints. In the case those appropriate registers should clobber a CC does a compiler add a suitable clobber rtx as written in define_split, or it just changes the registers names without any knowledge of a necessary clobber?
Thanks Dmitry. 

--- Г€Г±ГµГ®Г¤ГГ®ГҐ Г±Г®Г®ГЎГ№ГҐГГЁГҐ ---
 ГЋГІ ГЄГ®ГЈГ®: "Ian Lance Taylor" <iant@google.com> 
 ГЉГ®Г¬Гі: "Dmitry" <mittie@ukr.net> 
 Г„Г ГІГ : 28 Г ГЇГ°ГҐГ«Гї 2011, 17:58:17 
 Г’ГҐГ¬Г : Re: Back end question. 

> "Dmitry" <mittie@ukr.net> writes:
> 
> > But is there a chance that between a rtl generation and splitting an insn, a compiler could use that clobbered CC reg in some of intermediate phases, but after a register allocation it turns out that there shouldn't be any clobber at all?
> 
> Yes, there is a chance that that could happen. If you are lucky you
> will be able to clean it up after the splitting and reload, by observing
> the redundant set.
> 
> Ian
> 
> 