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> <span style="color: rgb(50, 49, 48); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; background-color: rgb(255, 255, 255); display: inline !important">I would love
to see Opt and CodeGen using the same pass manager (as my downstream project has already switched to NewPM in Opt).</span></div>
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FWIW I too would love to see CodeGen use the new PM. </div>
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Some months ago I worked on a patch, albeit mostly useful downstream, having BasicAA depend on LazyValueInfo but had to ultimately give up on it. With the old PM used in CodeGen I had lots of problems getting the dependencies right, debugging was difficult
and nobody could really provide answers on exactly how it was supposed to work.<br>
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So that said even if there are no performance gains there would definitely be other benefits.</div>
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-Markus</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of Fedor Sergeev via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Sent:</b> Wednesday, June 19, 2019 12:38 PM<br>
<b>To:</b> Charles.Zhang@sony.com; llvm-dev@lists.llvm.org<br>
<b>Cc:</b> joshua.magee@sony.com<br>
<b>Subject:</b> Re: [llvm-dev] Using the new pass manager for CodeGen</font>
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<div style="background-color:#FFFFFF">Hi, Charles,<br>
<br>
<div class="x_moz-cite-prefix">On 6/13/19 11:48 PM, via llvm-dev wrote:<br>
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<div>Hi,</div>
<div><br>
</div>
<div>I am looking into potentially porting CodeGen and some of the passes to using the new pass manager. Two questions:</div>
<div><br>
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<div>1. Has anybody made an attempt in this direction already? Maybe I am missing a branch out there that has started on this already. From what I can tell, there is no work in-tree in CodeGen that is aware of the new pass manager besides some assembly utilities
in BackendUtils.cpp. </div>
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</blockquote>
You are right, there is no activity in-tree in that direction to the best of my knowledge.<br>
And every time I was asking on LLVM devmtg if anybody working on that the answer was - "nay".<br>
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<div>My initial thoughts in this direction were that there would need to be some new pass manager machinery, for example, things like FunctionToMachineFunctionPassAdaptor that handles what MachineFunctionPass::runOnFunction used to do, along with the associated
AnalysisManager plumbing to understand units of MIR.<br>
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</blockquote>
Generally, what you describe is indeed a proper first step towards getting CodeGen on New-PM rails:<br>
- introduce IRUnits for Machine IR<br>
- provide generic handling for those new units everywhere in New-PM framework<br>
<br>
The next step would be to start moving at least one backend towards it, and thats where the initiative kinda stalls.<br>
I believe people working on CodeGen just do not find enough incentive to start that work.<br>
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<div>2. Are there any compile time improvements expected from porting CodeGen passes in the first place? As far as I can tell, the llc pass pipeline seems to be fairly well fixed in terms of phase ordering, and all the analyses are thrown out from opt anyway.</div>
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I would expect real savings just by reusing non-Machine-IR analyses.<br>
As soon as you use the same llvm state/module/etc for both Opt and CodeGen purposes
<br>
(thats what I believe many do, at least our JIT compiler does that). That will allow you<br>
to reuse analysis manager and thus keep every cached analysis there.<br>
<br>
I would love to see Opt and CodeGen using the same pass manager (as my downstream project has already switched to NewPM in Opt).<br>
<br>
Said that, perhaps analyses are not a current performance bottleneck in CodeGen (I bet instruction selection will always trump anything else).<br>
So this is more about overall consistency of operations rather than crazy performance gains.<br>
<br>
regards,<br>
Fedor.<br>
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<div>Thanks,<br>
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<div>Charles<br>
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