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Sean Silva via llvm-dev

2017-Jun-29 03:14 UTC

[llvm-dev] Definitive list of optimisations at each optimisation level

On Mon, Jun 26, 2017 at 5:04 AM, ORiordan, Martin <martin.oriordan at
intel.com> wrote:
> Thanks Sean and Silva.
>
>
>
> I guess what I was seeking was a URL that I could point (non-compiler)
> people at, but I guess no such reference exists.  What I can do if
> reference bot the source manager and use ‘-mllvm -debug-pass=Structure’
> for each optimisation level, and document that.  The downside is that this
> will continuously go out of data with each release.
>

Yeah, the nasty thing is that as each user of LLVM is running potentially
different pass pipelines, we don't really have a good way to write a
user-facing (or at least non-compiler-dev-facing) page describing the
optimizations that they should expect the compiler to do, as the compiler
developers using LLVM may have changed it. In theory, we could provide such
a page for the open-source clang. Such a page of course couldn't go into
massive detail about each pass and as such will likely be mostly describing
the basics.

Most of the information that users would care about is likely to not get
out of date very easily (e.g. we might switch GVN implementations, but the
way in which they differ isn't going to be relevant to such a document; we
might switch EarlyCSE to MemorySSA, but that isn't relevant to such a
document).

-- Sean Silva

>
>
> All the best,
>
>
>
>             MartinO
>
>
>
> PS: Movidius is now part of Intel, so I will be gradually switching to my
> Intel email address.
>
>
>
> *From:* Ryan Taylor [mailto:ryta1203 at gmail.com]
> *Sent:* Sunday, June 25, 2017 2:59 AM
> *To:* Sean Silva <chisophugis at gmail.com>
> *Cc:* Martin J. O'Riordan <martin.oriordan at movidius.com>;
llvm-dev <
> llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] Definitive list of optimisations at each
> optimisation level
>
>
>
> I agree, it's much clearer, it just takes runs at multiple opt levels
and
> therefore I don't find it to be a "one stop shop".
>
>
>
> On Jun 24, 2017 8:44 PM, "Sean Silva" <chisophugis at
gmail.com> wrote:
>
> Looking at PassManagerBuilder can be useful because there are sometimes
> comments giving some idea of the intent of the particular choice of passes,
> but it can be difficult to see the big picture of all the passes that are
> run because it is very parameterized and split across multiple subroutines.
>
>
>
> Running clang at O0 through O3 with -mllvm -debug-pass=Structure is
> generally more enlightening because then you see everything in one place
> for each optimization level.
>
>
>
> -- Sean Silva
>
>
>
> On Jun 24, 2017 12:54 PM, "Ryan Taylor" <ryta1203 at
gmail.com> wrote:
>
> Right but then you'll have to call each opt level. Have u looked in the
> pass manager?
>
>
>
> On Jun 24, 2017 3:52 PM, "Sean Silva via llvm-dev" <
> llvm-dev at lists.llvm.org> wrote:
>
> The most definitive list you can probably hope to get will be obtained by
> passing -mllvm -debug-pass=Structure to a clang invocation.
>
>
>
> -- Sean Silva
>
>
>
> On Jun 24, 2017 7:10 AM, "Martin J. O'Riordan via llvm-dev"
<
> llvm-dev at lists.llvm.org> wrote:
>
> I am often asked what optimisations “our” compiler performs at each
> level.  But “our” compiler is actually CLang/LLVM which we have retargeted
> to our proprietary target.
>
>
>
> Most of the work we do is in maintaining our target specific backend.
> Certainly there are optimisations that we do to take best advantage of our
> instruction set during lowering and instruction selection, and we have also
> added a couple of additional passes which manipulate the IR in advance of
> lowering to better shape it for our target.
>
>
>
> But in practice the vast majority of optimisations are contributed by the
> continuously evolving and excellent LLVM target independent passes, and
> have little or nothing to do with the work we do in our backend - though it
> is obviously directed/tuned by the various target call-backs and the target
> cost models.
>
>
>
> Is there a “one stop shop” list of the optimisation passes that LLVM
> performs, and identification of which are enabled by default for each of
> the 4 standard optimisation levels ‘-O0’ thru ‘-O3’?
>
>
>
> The reason that I ask, is that I really don’t have an honest or informed
> answer that I can provide to people when they ask, and I haven’t found a
> definitive statement of this in the LLVM documentation that I could refer
> them to.
>
>
>
> Thanks,
>
>
>
>             MartinO
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> --------------------------------------------------------------
> Intel Research and Development Ireland Limited
> Registered in Ireland
> Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
> Registered Number: 308263
>
> This e-mail and any attachments may contain confidential material for the
> sole use of the intended recipient(s). Any review or distribution by others
> is strictly prohibited. If you are not the intended recipient, please
> contact the sender and delete all copies.
>
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Martin J. O'Riordan via llvm-dev

2017-Jul-04 10:49 UTC

head link

[llvm-dev] Definitive list of optimisations at each optimisation level

Thanks Sean,

 

My apologies for previously writing “Thanks Sean and Silva”, I intended “Thanks
Sean and Ryan” - duh! - sleep deprived having just flown to the USA.

 

The dump is very enlightening for me, and very large - I hadn’t realised that
there were quite so many passes.  At ‘-O0’ there are ~70 passes, but at ‘-O1’ it
jumps to ~310 passes, and then ~340 passes at ‘-O2’ and ‘-O3’.  I will have to
carefully study these passes to see what optimisations they perform (if any),
though there are the obvious ones too.

 

One thing I observed, is that there are some passes that report:

 

Unnamed pass: implement Pass::getPassName()

 

This always appears after the final Target ‘AsmPrinter’ pass (“SHAVE Assembly
Printer” in our case) and appears to be from the ‘FPPassManager’, while the
other happens after ‘Global Variable Optimizer’ for optimisation levels of ‘-O1’
and higher and this seems to be the from the ‘MPPassManager’.  I am using the
release LLVM v4.0 sources, not the head revision.  I guess these are noise and
can be ignored.

 

All the best,

 

            MartinO

 

From: Sean Silva [mailto:chisophugis at gmail.com] 
Sent: 29 June 2017 04:15
To: ORiordan, Martin <martin.oriordan at intel.com>
Cc: Ryan Taylor <ryta1203 at gmail.com>; Martin J. O'Riordan
<martin.oriordan at movidius.com>; llvm-dev <llvm-dev at
lists.llvm.org>
Subject: Re: [llvm-dev] Definitive list of optimisations at each optimisation
level

 

 

 

On Mon, Jun 26, 2017 at 5:04 AM, ORiordan, Martin <martin.oriordan at
intel.com <mailto:martin.oriordan at intel.com> > wrote:

Thanks Sean and Silva.

 

I guess what I was seeking was a URL that I could point (non-compiler) people
at, but I guess no such reference exists.  What I can do if reference bot the
source manager and use ‘-mllvm -debug-pass=Structure’ for each optimisation
level, and document that.  The downside is that this will continuously go out of
data with each release.

 

 

Yeah, the nasty thing is that as each user of LLVM is running potentially
different pass pipelines, we don't really have a good way to write a
user-facing (or at least non-compiler-dev-facing) page describing the
optimizations that they should expect the compiler to do, as the compiler
developers using LLVM may have changed it. In theory, we could provide such a
page for the open-source clang. Such a page of course couldn't go into
massive detail about each pass and as such will likely be mostly describing the
basics.

 

Most of the information that users would care about is likely to not get out of
date very easily (e.g. we might switch GVN implementations, but the way in which
they differ isn't going to be relevant to such a document; we might switch
EarlyCSE to MemorySSA, but that isn't relevant to such a document).

 

-- Sean Silva

 

 

All the best,

 

            MartinO

 

PS: Movidius is now part of Intel, so I will be gradually switching to my Intel
email address.

 

From: Ryan Taylor [mailto:ryta1203 at gmail.com <mailto:ryta1203 at
gmail.com> ]
Sent: Sunday, June 25, 2017 2:59 AM
To: Sean Silva <chisophugis at gmail.com <mailto:chisophugis at
gmail.com> >
Cc: Martin J. O'Riordan <martin.oriordan at movidius.com
<mailto:martin.oriordan at movidius.com> >; llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org> >
Subject: Re: [llvm-dev] Definitive list of optimisations at each optimisation
level

 

I agree, it's much clearer, it just takes runs at multiple opt levels and
therefore I don't find it to be a "one stop shop".

 

On Jun 24, 2017 8:44 PM, "Sean Silva" <chisophugis at gmail.com
<mailto:chisophugis at gmail.com> > wrote:

Looking at PassManagerBuilder can be useful because there are sometimes comments
giving some idea of the intent of the particular choice of passes, but it can be
difficult to see the big picture of all the passes that are run because it is
very parameterized and split across multiple subroutines.

 

Running clang at O0 through O3 with -mllvm -debug-pass=Structure is generally
more enlightening because then you see everything in one place for each
optimization level.

 

-- Sean Silva

 

On Jun 24, 2017 12:54 PM, "Ryan Taylor" <ryta1203 at gmail.com
<mailto:ryta1203 at gmail.com> > wrote:

Right but then you'll have to call each opt level. Have u looked in the pass
manager?

 

On Jun 24, 2017 3:52 PM, "Sean Silva via llvm-dev" <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > wrote:

The most definitive list you can probably hope to get will be obtained by
passing -mllvm -debug-pass=Structure to a clang invocation.

 

-- Sean Silva

 

On Jun 24, 2017 7:10 AM, "Martin J. O'Riordan via llvm-dev"
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> >
wrote:

I am often asked what optimisations “our” compiler performs at each level.  But
“our” compiler is actually CLang/LLVM which we have retargeted to our
proprietary target.

 

Most of the work we do is in maintaining our target specific backend.  Certainly
there are optimisations that we do to take best advantage of our instruction set
during lowering and instruction selection, and we have also added a couple of
additional passes which manipulate the IR in advance of lowering to better shape
it for our target.

 

But in practice the vast majority of optimisations are contributed by the
continuously evolving and excellent LLVM target independent passes, and have
little or nothing to do with the work we do in our backend - though it is
obviously directed/tuned by the various target call-backs and the target cost
models.

 

Is there a “one stop shop” list of the optimisation passes that LLVM performs,
and identification of which are enabled by default for each of the 4 standard
optimisation levels ‘-O0’ thru ‘-O3’?

 

The reason that I ask, is that I really don’t have an honest or informed answer
that I can provide to people when they ask, and I haven’t found a definitive
statement of this in the LLVM documentation that I could refer them to.

 

Thanks,

 

            MartinO

 


_______________________________________________
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

 


_______________________________________________
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

 

--------------------------------------------------------------
Intel Research and Development Ireland Limited
Registered in Ireland
Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
Registered Number: 308263

This e-mail and any attachments may contain confidential material for the sole
use of the intended recipient(s). Any review or distribution by others is
strictly prohibited. If you are not the intended recipient, please contact the
sender and delete all copies.

 

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Sean Silva via llvm-dev

2017-Jul-04 19:47 UTC

head link

[llvm-dev] Definitive list of optimisations at each optimisation level

On Tue, Jul 4, 2017 at 3:49 AM, Martin J. O'Riordan <
martin.oriordan at movidius.com> wrote:
> Thanks Sean,
>
>
>
> My apologies for previously writing “Thanks Sean and Silva”, I intended
> “Thanks Sean and Ryan” - duh! - sleep deprived having just flown to the
USA.
>
>
>
> The dump is very enlightening for me, and very large - I hadn’t realised
> that there were quite so many passes.  At ‘-O0’ there are ~70 passes, but
> at ‘-O1’ it jumps to ~310 passes, and then ~340 passes at ‘-O2’ and ‘-O3’.
> I will have to carefully study these passes to see what optimisations they
> perform (if any), though there are the obvious ones too.
>
>
>
> One thing I observed, is that there are some passes that report:
>
>
>
> Unnamed pass: implement Pass::getPassName()
>
>
>
> This always appears after the final Target ‘AsmPrinter’ pass (“SHAVE
> Assembly Printer” in our case) and appears to be from the ‘FPPassManager’,
> while the other happens after ‘Global Variable Optimizer’ for optimisation
> levels of ‘-O1’ and higher and this seems to be the from the ‘
> MPPassManager’.  I am using the release LLVM v4.0 sources, not the head
> revision.  I guess these are noise and can be ignored.
>
I remember running into these before. I forget exactly what we ended up
discovering they were but I remember that it wasn't remarkable. Vaguely
remembering, I think the GlobalOpt one was something related to it
accessing function AA results or something like that. The reason it didn't
have a name is that it goes through some sort of adapter thing which
doesn't implement getPassName.

-- Sean Silva

>
>
> All the best,
>
>
>
>             MartinO
>
>
>
> *From:* Sean Silva [mailto:chisophugis at gmail.com]
> *Sent:* 29 June 2017 04:15
> *To:* ORiordan, Martin <martin.oriordan at intel.com>
> *Cc:* Ryan Taylor <ryta1203 at gmail.com>; Martin J. O'Riordan
<
> martin.oriordan at movidius.com>; llvm-dev <llvm-dev at
lists.llvm.org>
>
> *Subject:* Re: [llvm-dev] Definitive list of optimisations at each
> optimisation level
>
>
>
>
>
>
>
> On Mon, Jun 26, 2017 at 5:04 AM, ORiordan, Martin <
> martin.oriordan at intel.com> wrote:
>
> Thanks Sean and Silva.
>
>
>
> I guess what I was seeking was a URL that I could point (non-compiler)
> people at, but I guess no such reference exists.  What I can do if
> reference bot the source manager and use ‘-mllvm -debug-pass=Structure’
> for each optimisation level, and document that.  The downside is that this
> will continuously go out of data with each release.
>
>
>
>
>
> Yeah, the nasty thing is that as each user of LLVM is running potentially
> different pass pipelines, we don't really have a good way to write a
> user-facing (or at least non-compiler-dev-facing) page describing the
> optimizations that they should expect the compiler to do, as the compiler
> developers using LLVM may have changed it. In theory, we could provide such
> a page for the open-source clang. Such a page of course couldn't go
into
> massive detail about each pass and as such will likely be mostly describing
> the basics.
>
>
>
> Most of the information that users would care about is likely to not get
> out of date very easily (e.g. we might switch GVN implementations, but the
> way in which they differ isn't going to be relevant to such a document;
we
> might switch EarlyCSE to MemorySSA, but that isn't relevant to such a
> document).
>
>
>
> -- Sean Silva
>
>
>
>
>
> All the best,
>
>
>
>             MartinO
>
>
>
> PS: Movidius is now part of Intel, so I will be gradually switching to my
> Intel email address.
>
>
>
> *From:* Ryan Taylor [mailto:ryta1203 at gmail.com]
> *Sent:* Sunday, June 25, 2017 2:59 AM
> *To:* Sean Silva <chisophugis at gmail.com>
> *Cc:* Martin J. O'Riordan <martin.oriordan at movidius.com>;
llvm-dev <
> llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] Definitive list of optimisations at each
> optimisation level
>
>
>
> I agree, it's much clearer, it just takes runs at multiple opt levels
and
> therefore I don't find it to be a "one stop shop".
>
>
>
> On Jun 24, 2017 8:44 PM, "Sean Silva" <chisophugis at
gmail.com> wrote:
>
> Looking at PassManagerBuilder can be useful because there are sometimes
> comments giving some idea of the intent of the particular choice of passes,
> but it can be difficult to see the big picture of all the passes that are
> run because it is very parameterized and split across multiple subroutines.
>
>
>
> Running clang at O0 through O3 with -mllvm -debug-pass=Structure is
> generally more enlightening because then you see everything in one place
> for each optimization level.
>
>
>
> -- Sean Silva
>
>
>
> On Jun 24, 2017 12:54 PM, "Ryan Taylor" <ryta1203 at
gmail.com> wrote:
>
> Right but then you'll have to call each opt level. Have u looked in the
> pass manager?
>
>
>
> On Jun 24, 2017 3:52 PM, "Sean Silva via llvm-dev" <
> llvm-dev at lists.llvm.org> wrote:
>
> The most definitive list you can probably hope to get will be obtained by
> passing -mllvm -debug-pass=Structure to a clang invocation.
>
>
>
> -- Sean Silva
>
>
>
> On Jun 24, 2017 7:10 AM, "Martin J. O'Riordan via llvm-dev"
<
> llvm-dev at lists.llvm.org> wrote:
>
> I am often asked what optimisations “our” compiler performs at each
> level.  But “our” compiler is actually CLang/LLVM which we have retargeted
> to our proprietary target.
>
>
>
> Most of the work we do is in maintaining our target specific backend.
> Certainly there are optimisations that we do to take best advantage of our
> instruction set during lowering and instruction selection, and we have also
> added a couple of additional passes which manipulate the IR in advance of
> lowering to better shape it for our target.
>
>
>
> But in practice the vast majority of optimisations are contributed by the
> continuously evolving and excellent LLVM target independent passes, and
> have little or nothing to do with the work we do in our backend - though it
> is obviously directed/tuned by the various target call-backs and the target
> cost models.
>
>
>
> Is there a “one stop shop” list of the optimisation passes that LLVM
> performs, and identification of which are enabled by default for each of
> the 4 standard optimisation levels ‘-O0’ thru ‘-O3’?
>
>
>
> The reason that I ask, is that I really don’t have an honest or informed
> answer that I can provide to people when they ask, and I haven’t found a
> definitive statement of this in the LLVM documentation that I could refer
> them to.
>
>
>
> Thanks,
>
>
>
>             MartinO
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> --------------------------------------------------------------
> Intel Research and Development Ireland Limited
> Registered in Ireland
> Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
> Registered Number: 308263
>
> This e-mail and any attachments may contain confidential material for the
> sole use of the intended recipient(s). Any review or distribution by others
> is strictly prohibited. If you are not the intended recipient, please
> contact the sender and delete all copies.
>
>
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Sam Elliott via llvm-dev

2017-Jul-07 22:21 UTC

head link

[llvm-dev] Definitive list of optimisations at each optimisation level

I've just had to do the same as I'm also looking at the optimisations
that Clang/LLVM is performing on C code.

Given some of the names of latter passes seemed to include my target name (x86),
even at -O0, I wondered if some of these optimisations were target specific.

Thus, I ran `clang -mllvm -debug-pass=Structure -S -emit-llvm -xc /dev/null
--target='le64-unknown-unknown-unknown' -O$OPT_LEVEL` which seemed to
give me a shorter list with fewer to no target/machine-specific optimisations.

This gives ~21 passes at -O0, ~202 at -O1, ~225 for -Os and -Oz, and ~230 for
-O2, -O3, -Ofast (counting lines of output)

Assuming a "Pass Arguments" line specifies a new pass hierarchy inside
LLVM, I'm still unsure as to why there are 4 hierarchies in for example the
output of dumping the optimisations at -O1 (gist here:
https://gist.github.com/anonymous/e71193ad5200bcc87b226374b7924365
<https://gist.github.com/anonymous/e71193ad5200bcc87b226374b7924365> )

Sam
> On 4 Jul 2017, at 3:49 am, Martin J. O'Riordan via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 
> Thanks Sean,
>  
> My apologies for previously writing “Thanks Sean and Silva”, I intended
“Thanks Sean and Ryan” - duh! - sleep deprived having just flown to the USA.
>  
> The dump is very enlightening for me, and very large - I hadn’t realised
that there were quite so many passes.  At ‘-O0’ there are ~70 passes, but at
‘-O1’ it jumps to ~310 passes, and then ~340 passes at ‘-O2’ and ‘-O3’.  I will
have to carefully study these passes to see what optimisations they perform (if
any), though there are the obvious ones too.
>  
> One thing I observed, is that there are some passes that report:
>  
> Unnamed pass: implement Pass::getPassName()
>  
> This always appears after the final Target ‘AsmPrinter’ pass (“SHAVE
Assembly Printer” in our case) and appears to be from the ‘FPPassManager’, while
the other happens after ‘Global Variable Optimizer’ for optimisation levels of
‘-O1’ and higher and this seems to be the from the ‘MPPassManager’.  I am using
the release LLVM v4.0 sources, not the head revision.  I guess these are noise
and can be ignored.
>  
> All the best,
>  
>             MartinO
>  
> From: Sean Silva [mailto:chisophugis at gmail.com] 
> Sent: 29 June 2017 04:15
> To: ORiordan, Martin <martin.oriordan at intel.com>
> Cc: Ryan Taylor <ryta1203 at gmail.com>; Martin J. O'Riordan
<martin.oriordan at movidius.com>; llvm-dev <llvm-dev at
lists.llvm.org>
> Subject: Re: [llvm-dev] Definitive list of optimisations at each
optimisation level
>  
>  
>  
> On Mon, Jun 26, 2017 at 5:04 AM, ORiordan, Martin <martin.oriordan at
intel.com <mailto:martin.oriordan at intel.com>> wrote:
>> Thanks Sean and Silva.
>>  
>> I guess what I was seeking was a URL that I could point (non-compiler)
people at, but I guess no such reference exists.  What I can do if reference bot
the source manager and use ‘-mllvm -debug-pass=Structure’ for each optimisation
level, and document that.  The downside is that this will continuously go out of
data with each release.
>  
>  
> Yeah, the nasty thing is that as each user of LLVM is running potentially
different pass pipelines, we don't really have a good way to write a
user-facing (or at least non-compiler-dev-facing) page describing the
optimizations that they should expect the compiler to do, as the compiler
developers using LLVM may have changed it. In theory, we could provide such a
page for the open-source clang. Such a page of course couldn't go into
massive detail about each pass and as such will likely be mostly describing the
basics.
>  
> Most of the information that users would care about is likely to not get
out of date very easily (e.g. we might switch GVN implementations, but the way
in which they differ isn't going to be relevant to such a document; we might
switch EarlyCSE to MemorySSA, but that isn't relevant to such a document).
>  
> -- Sean Silva
>  
>>  
>> All the best,
>>  
>>             MartinO
>>  
>> PS: Movidius is now part of Intel, so I will be gradually switching to
my Intel email address.
>>  
>> From: Ryan Taylor [mailto:ryta1203 at gmail.com <mailto:ryta1203 at
gmail.com>]
>> Sent: Sunday, June 25, 2017 2:59 AM
>> To: Sean Silva <chisophugis at gmail.com <mailto:chisophugis at
gmail.com>>
>> Cc: Martin J. O'Riordan <martin.oriordan at movidius.com
<mailto:martin.oriordan at movidius.com>>; llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
>> Subject: Re: [llvm-dev] Definitive list of optimisations at each
optimisation level
>>  
>> I agree, it's much clearer, it just takes runs at multiple opt
levels and therefore I don't find it to be a "one stop shop".
>>  
>> On Jun 24, 2017 8:44 PM, "Sean Silva" <chisophugis at
gmail.com <mailto:chisophugis at gmail.com>> wrote:
>>> Looking at PassManagerBuilder can be useful because there are
sometimes comments giving some idea of the intent of the particular choice of
passes, but it can be difficult to see the big picture of all the passes that
are run because it is very parameterized and split across multiple subroutines.
>>>  
>>> Running clang at O0 through O3 with -mllvm -debug-pass=Structure is
generally more enlightening because then you see everything in one place for
each optimization level.
>>>  
>>> -- Sean Silva
>>>  
>>> On Jun 24, 2017 12:54 PM, "Ryan Taylor" <ryta1203 at
gmail.com <mailto:ryta1203 at gmail.com>> wrote:
>>>> Right but then you'll have to call each opt level. Have u
looked in the pass manager?
>>>>  
>>>> On Jun 24, 2017 3:52 PM, "Sean Silva via llvm-dev"
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
>>>>> The most definitive list you can probably hope to get will
be obtained by passing -mllvm -debug-pass=Structure to a clang invocation.
>>>>>  
>>>>> -- Sean Silva
>>>>>  
>>>>> On Jun 24, 2017 7:10 AM, "Martin J. O'Riordan via
llvm-dev" <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>>>>> I am often asked what optimisations “our” compiler
performs at each level.  But “our” compiler is actually CLang/LLVM which we have
retargeted to our proprietary target.
>>>>>>  
>>>>>> Most of the work we do is in maintaining our target
specific backend.  Certainly there are optimisations that we do to take best
advantage of our instruction set during lowering and instruction selection, and
we have also added a couple of additional passes which manipulate the IR in
advance of lowering to better shape it for our target.
>>>>>>  
>>>>>> But in practice the vast majority of optimisations are
contributed by the continuously evolving and excellent LLVM target independent
passes, and have little or nothing to do with the work we do in our backend -
though it is obviously directed/tuned by the various target call-backs and the
target cost models.
>>>>>>  
>>>>>> Is there a “one stop shop” list of the optimisation
passes that LLVM performs, and identification of which are enabled by default
for each of the 4 standard optimisation levels ‘-O0’ thru ‘-O3’?
>>>>>>  
>>>>>> The reason that I ask, is that I really don’t have an
honest or informed answer that I can provide to people when they ask, and I
haven’t found a definitive statement of this in the LLVM documentation that I
could refer them to.
>>>>>>  
>>>>>> Thanks,
>>>>>>  
>>>>>>             MartinO
>>>>>>  
>>>>>> 
>>>>>> _______________________________________________
>>>>>> 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
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>>>>  
>>>>> 
>>>>> _______________________________________________
>>>>> 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
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>>  
>> 
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Archibald Sam Elliott
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PhD Student, PLSE Group

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llvm dev - Jul 2017 - Definitive list of optimisations at each optimisation level

[llvm-dev] Definitive list of optimisations at each optimisation level

[llvm-dev] Definitive list of optimisations at each optimisation level

[llvm-dev] Definitive list of optimisations at each optimisation level

[llvm-dev] Definitive list of optimisations at each optimisation level