On 03/16/2011 03:32 AM, Georg-Johann Lay wrote: > Richard Henderson schrieb: >> On 03/11/2011 05:43 AM, Georg-Johann Lay wrote: >>> I did not find a way to make this work together with -mcall-prologues. >>> Please let me know if you have suggestion on how call prologues can be >>> combine with tail calls. >> >> You need a new symbol in libgcc for this. It should be easy enough to have >> the sibcall epilogue load up Z+EIND before jumping to the new symbol >> (perhaps called __sibcall_restores__). This new symbol would be just like >> the existing __epilogue_restores__ except that it would finish with an >> eijmp/ijmp instruction (depending on multilib) instead of a ret instruction. > > The point is that the intent of -mprologue-saves is to save program > memory space (flash). If we load the callee's address in the epilogue, > the epilogue's size will increase. Moreover, adding an other lengthy > function besides __epilogue_restores__ to libgcc, that will increase > code size because in many cases we will see both epilogue flavors > being dragged into application.
All true, but supposing there are enough tail calls then on balance you'll still save flash space. An intermediate alternative is to simply override TARGET_CALL_PROLOGUES in sibcall epilogues. I.e. let __prologue_saves__ be generated as usual, and __epilogue_restores__ be generated as usual for normal epilogues, but test for sibcall_p in computing "minimize". r~
