https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78332
amker at gcc dot gnu.org changed:
What |Removed |Added
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CC| |amker at gcc dot gnu.org
--- Comment #1 from amker at gcc dot gnu.org ---
I think there are two issues here.
First is the negative cost. It's because we book saved cost of auto-increment
addressing mode to use-cand cost, rather than the candidate itself. Given it
only makes sense to use auto-increment candidate for the use why it is created,
I think we can change the strategy by booking saved cost to candidate it self.
This issue could be improved, but not a bug I think.
Second is auto-increment candidate is preferred too much. This is again a cost
model issue. A. to how much auto-increment should be preferred; B. should
register cost be tightened because currently the effect is only spill cost in
loop is considered, cost of epilogue/prologue pop/push of more registers is not
handled. Also addressing mode costs returned by backend need to be considered
too. I will further investigate this later.
