[llvm-dev] Conditional analysis before inliner

[Jatin Bhateja via llvm-dev]

I do not think we have this framework of conditionally kicking in analysis
passes. But one can always do "intelligent" prior setting of attribute over
function which can be checked in getAnalysisUsage for a perticular pass to
conditionally enable needed analysis.

Cheers
Jatin

On Tue, 24 Apr 2018, 04:33 Friedman, Eli via llvm-dev, <
llvm-dev at lists.llvm.org> wrote:

> I probably wouldn't worry about the cost of LoopInfo; it's relatively
> cheap to compute.  But if you're really concerned, you can run your pass
> after a pass which preserves LoopInfo (so it's free because it was already
> computed).  Or you can stick your code into an existing pass which requires
> LoopInfo anyway, like LoopIdiomRecognize.
>
> -Eli
>
> On 4/23/2018 3:37 PM, Anom LLVM wrote:
>
> Thanks for the answer Eli.
>
> I think I was a little too vague in my question. The program has the
> following structure:
> void foo() {
>   bar();
> }
>
> void bar() {
>   for (..) {
>        __builtin_compute()
>   }
> }
>
> We would like to use scalar evolution + loopinfowrapperpass inside
> instcombine only if __builtin_compute is present. instcombine can convert
> the loop into a single builtin ie.
>
> void bar() {
>   __builtin_wide_compute();
> }
>
> When the inliner runs on foo(), we want bar() to already have the
> transformation to reflect the cost of the inlining decision more
> accurately.
>
> I do see that scalar evolution is a lazy but loopwrapinfopass is not. Is
> there a way to run these two analysis passes conditionally before inlining?
>
> Thanks,
>
> Stan
>
>
>
>
>
>
> On Fri, Apr 20, 2018 at 1:55 PM, Friedman, Eli <efriedma at codeaurora.org>
> wrote:
>
>> On 4/19/2018 1:57 PM, Anom LLVM via llvm-dev wrote:
>>
>>> Hi,
>>>
>>> I have pass phase ordering question.
>>>
>>> I am interested in performing a transformation that matches several LLVM
>>> IR instructions and converts them to a single builtin. This sort of
>>> transformation must occur prior to inlining because inlining needs to
>>> analyze cost of the builtin. However, the LLVM IR -> builtin transformation
>>> requires scalar evolution which typically doesn't run until after the
>>> inliner.
>>>
>>
>> This isn't right, or at least, not the complete picture; loop
>> optimization passes run interleaved with the inliner.  (Try looking at the
>> output of "-debug-pass=Executions" to see exactly what's happening.)
>>
>> My question is, is there a way to run scalar evolution conditionally
>>> prior to inlining? I'd like to leave compile time unaffected if my code
>>> doesn't contain any of these builtins.
>>>
>>
>> ScalarEvolution is lazy, so it's essentially free if you don't query it.
>>
>> -Eli
>>
>> --
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>> Linux Foundation Collaborative Project
>>
>>
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
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