[llvm-dev] Benchmark GlobalsModRef in non-LTO pass pipeline
Chandler Carruth via llvm-dev
llvm-dev at lists.llvm.org
Mon Aug 10 11:22:35 PDT 2015
Cool, I was going to suggest exactly that variation of the change. =] Now
that there is no update API, it should be straight forward for *every* pass
to preserve AA. I'll see if I can simulate this in the current pass manager
in some way.
On Mon, Aug 10, 2015 at 8:06 AM James Molloy via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> To amend what I said earlier, after a lot more investigation it turns out
> the problem is that a bunch of optimization passes don't preserve
> AliasAnalysis. If I add AU.setPreserved<AliasAnalysis> to a bunch of them,
> passes such as LICM end up seeing GMR in its alias analysis chain. That's
> when I start to see improvements.
> On Mon, 10 Aug 2015 at 10:06 James Molloy <james at jamesmolloy.co.uk> wrote:
>> Hi Chandler,
>> Sorry it took so long for me to get to this. I'm very keen to get GMR
>> enabled in the non-LTO pipeline. I see nontrivial perf improvements in a
>> bunch of workloads I care about with it enabled, but with a patch applied
>> to run GMR again after the LoopPasses but before the FunctionPasses.
>> I've found this is critical - LICM needs GMR available, and the
>> passmanager kills it by the time the early LICM is run.
>> I'd be really keen to get this enabled by default, with that extra run
>> added. I assume the need for this extra run will evaporate with the new
>> pass manager?
>> On Thu, 6 Aug 2015 at 03:45 Chandler Carruth <chandlerc at gmail.com> wrote:
>>> Greetings folks!
>>> I would like to enable globalsmodref-aa in the non-LTO pass pipeline so
>>> that it gets tested more and there are fewer differences between the two.
>>> For all of my benchmarks, this is performance neutral, but I'd appreciate
>>> others benchmarking this combination to see if they see any benefits or
>>> You can demo this mode easily: -mllvm -enable-non-lto-gmr
>>> Please let me know!
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org http://llvm.cs.uiuc.edu
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