llvm dev - Nov 2018 - Completeness of -print-after-all

Hi,

I recently worked on an issue where I realized that -print-after-all does not
cover all passes run by the pass manager. E.g. it seems that loop passes are
not fully covered and I could find that loop transformations showed up in the
dump of the next non-loop pass (which happened to be 'Combine redundant
instructions' and that was rather confusing).

Specifying both -print-before-all and -print-after-all and doing some grepping
gives me the following where we see two back-to-back 'Before' dumps
which
should not be possible.

*** IR Dump Before LCSSA Verifier ***
*** IR Dump After LCSSA Verifier ***
*** IR Dump Before Loop-Closed SSA Form Pass ***
*** IR Dump After Loop-Closed SSA Form Pass ***
*** IR Dump Before Unroll loops ***
*** IR Dump Before Combine redundant instructions ***
*** IR Dump After Combine redundant instructions ***

Maybe there are good reasons for making this hard to fix but to me it seems
like a rather severe deficiency so I wonder if this is widely known and if there
are any plans to improve it?

-Markus

Markus,

Loop passes are kinda unique compared to func/module passes in that they
could destroy the loop they worked on. And there might be no loop to print
after that (btw, there is a known bug in new pass manager where it tries to
print deleted loop in this situation - nothing good happens!).

In your case loop unroll can fully uroll the loop, essentially removing the
Loop.

If you have suggestions on how to improve behavior in such cases I would be
happy to discuss this further.

regards,
Fedor

8 нояб. 2018 г. 12:38 пользователь "Markus Lavin via llvm-dev" <
llvm-dev at lists.llvm.org> написал:

Hi,

I recently worked on an issue where I realized that -print-after-all does
not
cover all passes run by the pass manager. E.g. it seems that loop passes are
not fully covered and I could find that loop transformations showed up in
the
dump of the next non-loop pass (which happened to be 'Combine redundant
instructions' and that was rather confusing).

Specifying both -print-before-all and -print-after-all and doing some
grepping
gives me the following where we see two back-to-back 'Before' dumps
which
should not be possible.

*** IR Dump Before LCSSA Verifier ***
*** IR Dump After LCSSA Verifier ***
*** IR Dump Before Loop-Closed SSA Form Pass ***
*** IR Dump After Loop-Closed SSA Form Pass ***
*** IR Dump Before Unroll loops ***
*** IR Dump Before Combine redundant instructions ***
*** IR Dump After Combine redundant instructions ***

Maybe there are good reasons for making this hard to fix but to me it seems
like a rather severe deficiency so I wonder if this is widely known and if
there
are any plans to improve it?

-Markus

_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Fedor,

Yes that is what happens in my case that the loop is fully unrolled and hence
‘removed’.

My objection though is that there is still IR that could be dumped (i.e. the
function containing the loop that was removed or the entire module) and that is
what I want to have dumped after each pass when I specify -print-after-all. Of
course there may be certain implementation details that could make this hard to
achieve but ideally I would like to have a reliable option that dumps the entire
IR (complete enough to import into opt and run additional passes on) after each
individual pass (module, function, loop or whatever).

Doesn’t that make sense?

Regards,
Markus


From: Fedor Sergeev <fedor.v.sergeev at gmail.com>
Sent: Thursday, November 8, 2018 11:06 AM
To: Markus Lavin <markus.lavin at ericsson.com>
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Completeness of -print-after-all

Markus,

Loop passes are kinda unique compared to func/module passes in that they could
destroy the loop they worked on. And there might be no loop to print after that
(btw, there is a known bug in new pass manager where it tries to print deleted
loop in this situation - nothing good happens!).

In your case loop unroll can fully uroll the loop, essentially removing the
Loop.

If you have suggestions on how to improve behavior in such cases I would be
happy to discuss this further.

regards,
Fedor

8 нояб. 2018 г. 12:38 пользователь "Markus Lavin via llvm-dev"
<llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
написал:
Hi,

I recently worked on an issue where I realized that -print-after-all does not
cover all passes run by the pass manager. E.g. it seems that loop passes are
not fully covered and I could find that loop transformations showed up in the
dump of the next non-loop pass (which happened to be 'Combine redundant
instructions' and that was rather confusing).

Specifying both -print-before-all and -print-after-all and doing some grepping
gives me the following where we see two back-to-back 'Before' dumps
which
should not be possible.

*** IR Dump Before LCSSA Verifier ***
*** IR Dump After LCSSA Verifier ***
*** IR Dump Before Loop-Closed SSA Form Pass ***
*** IR Dump After Loop-Closed SSA Form Pass ***
*** IR Dump Before Unroll loops ***
*** IR Dump Before Combine redundant instructions ***
*** IR Dump After Combine redundant instructions ***

Maybe there are good reasons for making this hard to fix but to me it seems
like a rather severe deficiency so I wonder if this is widely known and if there
are any plans to improve it?

-Markus

_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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