llvm dev - Jun 2020 - optnone/skipping passes in the new pass manager

On Mon, Jun 8, 2020 at 7:11 AM Robinson, Paul <paul.robinson at sony.com>
wrote:
> When the optnone design was being discussed, Chandler specifically
> rejected having the pass manager involved in the decision (which was the
> original proposed design).  Assuming he still feels the same way now, if
> the existing `skipFunction` calls aren’t being executed under the new pass
> manager, then each pass that has that call will need to be modified
> accordingly (added to the NPM path or moved to some common point).  It
> would be best if the `skipFunction` calls were handled consistently in all
> passes so that it would become part of the normal pass boilerplate.
>
Makes sense, thanks for the background. I'll see if there's a clean way
to
make this functionality easy to use in the NPM.
>
>
> I suspect any `skipFunction` or opt-bisection tests have been written to
> force the old pass manager, which is why defaulting to the new pass manager
> doesn’t fail anywhere.
>
I took a closer look at some optnone tests and they use opt instead of
clang. opt still defaults to the legacy pass manager regardless of clang's
default.
> --paulr
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of
*Arthur
> Eubanks via llvm-dev
> *Sent:* Sunday, June 7, 2020 7:59 PM
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [llvm-dev] optnone/skipping passes in the new pass manager
>
>
>
> Looking through some of the remaining test failures under the new pass
> manager, I've narrowed down one of the failures in GWPAsan(!) to the
fact
> that the new pass manager doesn't properly skip passes like the old
pass
> manager. For example, when a function is marked optnone, or when using
> https://llvm.org/docs/OptBisect.html.
>
>
>
> Lots of passes (e.g. SROA) will do the following under the legacy pass
> manager:
>
>
>
>   bool runOnFunction(Function &F) override {
>     if (skipFunction(F))
>       return false;
>
>     // do pass
>
>   }
>
>
>
> What's the right way to proceed with this? There are 50-100 calls to
> skipFunction() in legacy passes. This doesn't even account for other
types
> of IR units, like skipModule(Module&).
>
>
>
> I suppose it's possible to manually go in and add in the same check in
the
> new passes, but that seems tedious (and how do you test that at scale?
> clearly there aren't many tests for it right now since check-llvm
passes
> under the new pass manager). An alternative of skipping passes at the pass
> manager level would require marking each pass as necessary/optional (I
> think...).
>
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Maybe you could change the default PM in opt and see what fails?
--paulr

From: Arthur Eubanks <aeubanks at google.com>
Sent: Monday, June 8, 2020 5:52 PM
To: Robinson, Paul <paul.robinson at sony.com>
Cc: Chandler Carruth <chandlerc at gmail.com>; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] optnone/skipping passes in the new pass manager



On Mon, Jun 8, 2020 at 7:11 AM Robinson, Paul <paul.robinson at
sony.com<mailto:paul.robinson at sony.com>> wrote:
When the optnone design was being discussed, Chandler specifically rejected
having the pass manager involved in the decision (which was the original
proposed design).  Assuming he still feels the same way now, if the existing
`skipFunction` calls aren’t being executed under the new pass manager, then each
pass that has that call will need to be modified accordingly (added to the NPM
path or moved to some common point).  It would be best if the `skipFunction`
calls were handled consistently in all passes so that it would become part of
the normal pass boilerplate.
Makes sense, thanks for the background. I'll see if there's a clean way
to make this functionality easy to use in the NPM.

I suspect any `skipFunction` or opt-bisection tests have been written to force
the old pass manager, which is why defaulting to the new pass manager doesn’t
fail anywhere.
I took a closer look at some optnone tests and they use opt instead of clang.
opt still defaults to the legacy pass manager regardless of clang's default.
--paulr

From: llvm-dev <llvm-dev-bounces at lists.llvm.org<mailto:llvm-dev-bounces
at lists.llvm.org>> On Behalf Of Arthur Eubanks via llvm-dev
Sent: Sunday, June 7, 2020 7:59 PM
To: llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at
lists.llvm.org>>
Subject: [llvm-dev] optnone/skipping passes in the new pass manager

Looking through some of the remaining test failures under the new pass manager,
I've narrowed down one of the failures in GWPAsan(!) to the fact that the
new pass manager doesn't properly skip passes like the old pass manager. For
example, when a function is marked optnone, or when using
https://llvm.org/docs/OptBisect.html<https://urldefense.com/v3/__https:/llvm.org/docs/OptBisect.html__;!!JmoZiZGBv3RvKRSx!t3zrtZFFWm0ifdWgL9SiWSNETodW3pMSJ8m8YWqK139cicFp_U1juO0D90-VinpUWg$>.

Lots of passes (e.g. SROA) will do the following under the legacy pass manager:

  bool runOnFunction(Function &F) override {
    if (skipFunction(F))
      return false;
    // do pass
  }

What's the right way to proceed with this? There are 50-100 calls to
skipFunction() in legacy passes. This doesn't even account for other types
of IR units, like skipModule(Module&).

I suppose it's possible to manually go in and add in the same check in the
new passes, but that seems tedious (and how do you test that at scale? clearly
there aren't many tests for it right now since check-llvm passes under the
new pass manager). An alternative of skipping passes at the pass manager level
would require marking each pass as necessary/optional (I think...).
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Hmm it looks like getting NPM to work with opt is non-trivial. Only a small
portion of the opt functionality works with NPM :(

On Mon, Jun 8, 2020 at 3:36 PM Robinson, Paul <paul.robinson at sony.com>
wrote:
> Maybe you could change the default PM in opt and see what fails?
>
> --paulr
>
>
>
> *From:* Arthur Eubanks <aeubanks at google.com>
> *Sent:* Monday, June 8, 2020 5:52 PM
> *To:* Robinson, Paul <paul.robinson at sony.com>
> *Cc:* Chandler Carruth <chandlerc at gmail.com>; llvm-dev at
lists.llvm.org
> *Subject:* Re: [llvm-dev] optnone/skipping passes in the new pass manager
>
>
>
>
>
>
>
> On Mon, Jun 8, 2020 at 7:11 AM Robinson, Paul <paul.robinson at
sony.com>
> wrote:
>
> When the optnone design was being discussed, Chandler specifically
> rejected having the pass manager involved in the decision (which was the
> original proposed design).  Assuming he still feels the same way now, if
> the existing `skipFunction` calls aren’t being executed under the new pass
> manager, then each pass that has that call will need to be modified
> accordingly (added to the NPM path or moved to some common point).  It
> would be best if the `skipFunction` calls were handled consistently in all
> passes so that it would become part of the normal pass boilerplate.
>
> Makes sense, thanks for the background. I'll see if there's a clean
way to
> make this functionality easy to use in the NPM.
>
>
>
> I suspect any `skipFunction` or opt-bisection tests have been written to
> force the old pass manager, which is why defaulting to the new pass manager
> doesn’t fail anywhere.
>
> I took a closer look at some optnone tests and they use opt instead of
> clang. opt still defaults to the legacy pass manager regardless of
clang's
> default.
>
> --paulr
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of
*Arthur
> Eubanks via llvm-dev
> *Sent:* Sunday, June 7, 2020 7:59 PM
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [llvm-dev] optnone/skipping passes in the new pass manager
>
>
>
> Looking through some of the remaining test failures under the new pass
> manager, I've narrowed down one of the failures in GWPAsan(!) to the
fact
> that the new pass manager doesn't properly skip passes like the old
pass
> manager. For example, when a function is marked optnone, or when using
> https://llvm.org/docs/OptBisect.html
>
<https://urldefense.com/v3/__https:/llvm.org/docs/OptBisect.html__;!!JmoZiZGBv3RvKRSx!t3zrtZFFWm0ifdWgL9SiWSNETodW3pMSJ8m8YWqK139cicFp_U1juO0D90-VinpUWg$>
> .
>
>
>
> Lots of passes (e.g. SROA) will do the following under the legacy pass
> manager:
>
>
>
>   bool runOnFunction(Function &F) override {
>     if (skipFunction(F))
>       return false;
>
>     // do pass
>
>   }
>
>
>
> What's the right way to proceed with this? There are 50-100 calls to
> skipFunction() in legacy passes. This doesn't even account for other
types
> of IR units, like skipModule(Module&).
>
>
>
> I suppose it's possible to manually go in and add in the same check in
the
> new passes, but that seems tedious (and how do you test that at scale?
> clearly there aren't many tests for it right now since check-llvm
passes
> under the new pass manager). An alternative of skipping passes at the pass
> manager level would require marking each pass as necessary/optional (I
> think...).
>
>
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