Re: Why IRA stores in frame, not in callee-saved reg?

[Jeff Law <law at redhat dot com>]

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On 03/08/11 04:36, Georg-Johann Lay wrote:

> 
> IRA doues not take into account costs implied by generating new stack
> slots and setting up frame pointer. AFAIK there is no hook to
> influence that. How can a target describe costs generated by setting
> up stack slots and accessing them?
IRA isn't particularly good about accounting for prologue/epilogue
costs, both the saves/restores and FP setup.

Part of the problem is the cost is really amortized across potentially
many allocnos which potentially use the callee-saved registers.
Unfortunately, there's no way to know that apriori.  It's an issue Vlad
and I have discussed, but we haven't come to any kind of conclusions for
how to better model the costs of the prologue/epilogue vs the savings of
allocing more allocnos to callee-saved hard regs vs caller-saved hard
regs or memory.

jeff
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