[LLVMdev] IR Passes and TargetTransformInfo: Straw Man

Shuxin Yang
Thu, 18 Jul 2013 02:09:54 -0000

Andy and I briefly discussed this  the other day, we have not yet got
chance to list a detailed pass order
for the pre- and post- IPO scalar optimizations.

This is wish-list in our mind:

pre-IPO:  based on the ordering he propose, get rid of the inlining (or
just inline tiny func), get rid of
                all loop xforms...

post-IPO: get rid of inlining, or maybe we still need it, only perform
the inling to to callee which now become tiny.
                enable the loop xforms.

                 The SCC pass manager seems to be important inling,  no
matter how the inling looks like in the future,
                 I think the passmanager is still useful for scalar
opt.  It enable us to achieve cheap inter-procedural
                 opt hands down in the sense that we can optimize
callee, analyze it, and feedback the detailed whatever
                 info  back to caller (say info like "the callee already
return constant 5", the "callee return value in 5-10",
                 and such info is difficult to obtain and IPO stage, as
it can not afford to take such closer look.

I think it is too early to discuss the pre-IPO and post-IPO thing, let
us focus on what Andy is proposing.


On 7/17/13 6:04 PM, Sean Silva wrote:
> There seems to be a lot of interest recently in LTO. How do you see
> the situation of splitting the IR passes between per-TU processing and
> multi-TU ("link time") processing?
>
> -- Sean Silva
>
>
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