[llvm-dev] Debugify and Verify-each mode

[Vedant Kumar via llvm-dev]

> On Mar 16, 2018, at 2:30 PM, Son Tuan VU <sontuan.vu119 at gmail.com> wrote:
> 
> Hi Vedant,
> 
> Thank you for your reply. I think I can make this debugify-each mode, but I guess this is reserved for your GSoC project ?

No, there's no reserved work. If you'd like to work on this I encourage you to do so. There's plenty of other work slated for the GSoC project. That said, let's make sure to sync up on the mailing lists to make sure work isn't being duplicated.


> However, if I understand correctly, we do not want to take the output of the first check-debugify (I mean the .ll file with potentially all the WARNINGs and ERRORs after the first pass) as input for the second debugify. What we need is to take the fresh output of clang -Xclang -emit-llvm -disable-O0-optnone -S and iteratively test each optimization. Am I right?

The intermediate textual output is all irrelevant. And clang isn't in the picture here. Opt's regular mode of operation is to run pass1, then run pass2, etc. In the debugify-each mode, this instead looks like: debugify, pass1, check-debugify, strip debug info, debugify, pass2, etc. etc.

vedant


> 
> Cheers,
> 
> 
> Son Tuan Vu
> 
> On Thu, Mar 15, 2018 at 4:05 AM, Vedant Kumar <vsk at apple.com <mailto:vsk at apple.com>> wrote:
> Hi Son Tuan,
> 
> Thanks for taking a look at this :). Responses inline --
> 
>> On Mar 14, 2018, at 8:11 AM, Son Tuan VU <sontuan.vu119 at gmail.com <mailto:sontuan.vu119 at gmail.com>> wrote:
>> 
>> Hi Vedant, hi all,
>> 
>> My goal is to measure debug info loss of each optimization pass in LLVM. I am trying to create a debugify-each mode in opt, inspired by verify-each mode which is supposed to already work.
> 
> + Anastasis, who's interested in working on this as well. There's definitely enough work to go around: once we can measure debug info loss after each pass, we'll need a testing harness.
> 
> 
>> However, if I understand correctly, the verify-each mode (triggered by -verify-each option in opt) only works when we provide a pass list or a pass pipeline.
> 
> Yes, you're correct.
> 
> 
>> Is this intended? I mean, why do not let people verify each pass in -O{1,2,3} pipeline?
> 
> That's a good question! Like you, I assumed -verify-each "does the right thing" when you pass -O1/-O2/etc. to opt.
> 
> I'm not sure if the current behavior is intended (hopefully others will chime in about this :). If no one does, please file a bug.
> 
> I imagine this is pretty simple to fix. You can just define and use custom pass managers within opt which inject debugify passes as needed:
> 
>>> // In opt.cpp:
>>> 
>>> class DebugifyEachFunctionPassManager : public legacy::FunctionPassManager {
>>> public:
>>>   explicit DebugifyEachFunctionPassManager(Module *M)
>>>       : FunctionPassManager(M) {}
>>> 
>>>   void add(Pass *P) override {
>>>     // FunctionPassManager::add(<debugify>)
>>>     FunctionPassManager::add(P);
>>>   }
>>> };
> 
> 
>> My second question is more about debugify: what should be the best way to debugify each pass? Adding a debugify-each mode would make the output unreadable!
> 
> The intermediate output is all irrelevant. I think it'd be best to simply throw it away. What really matters are the debug info loss statistics: we should capture these stats after each pass and dump them as JSON, at the end of the pipeline.
> 
> vedant
> 
> 
>> Maybe writing a script that collects all optimization options (like -mem2reg or -constmerge), then pass each one of them to opt with -enable-debugify so that we have 1 output file for each debugified pass?
>> 
>> Thank you for your help,
>> 
>> Son Tuan Vu
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180316/60d7042b/attachment.html>