llvm dev - Dec 2015 - Is there a way to pass Optimization passes to clang?

0 down vote favorite
<http://stackoverflow.com/questions/34049511/how-to-pass-optimization-passes-to-clang#>

I'm trying to debug an issue for a new target where a testcase fails with
-O1 optimization and passes with -O0 optimization.

I got a list of optimization passes being performed when 'clang -O1' is
called like this:

llvm-as < /dev/null | opt -O1 -disable-output -debug-pass=Arguments

Which results in:

Pass Arguments:  -no-aa -tbaa -targetlibinfo -basicaa -notti -preverify
-domtree -verify -simplifycfg -domtree -sroa -early-cse -lower-expect
Pass Arguments:  -targetlibinfo -no-aa -tbaa -basicaa -notti -globalopt
-ipsccp -deadargelim -instcombine -simplifycfg -basiccg -prune-eh
-inline-cost -always-inline -functionattrs -sroa -domtree -early-cse
-simplify-libcalls -lazy-value-info -jump-threading -correlated-propagation
-simplifycfg -instcombine -tailcallelim -simplifycfg -reassociate -domtree
-loops -loop-simplify -lcssa -loop-rotate -licm -lcssa -loop-unswitch
-instcombine -scalar-evolution -loop-simplify -lcssa -indvars -loop-idiom
-loop-deletion -loop-unroll -memdep -memcpyopt -sccp -instcombine
-lazy-value-info -jump-threading -correlated-propagation -domtree -memdep
-dse -adce -simplifycfg -instcombine -strip-dead-prototypes -preverify
-domtree -verify

(BTW: why are there two Pass Arguments lists returned there?)

Now my intent is to figure out which optimization pass is causing the
problem by trying each one until I hit the same problem as with -O1, but
clang itself doesn't seem to allow these commandline options, for example:

clang -loops -lcssa ....

Results in:

clang: warning: -loops: 'linker' input unused
clang: warning: -lcssa: 'linker' input unused


(Makes sense as it conflicts with the -l command line opt)
So is there a way to pass these in on the command line? (or bonus if
there's a way to specify a file which contains a list of optimization
passes to perform)


Note: I realize there must be a way to break everything up into stages and
use *opt* at some point and pass the optimization command line options to
it, but I've got a pretty large set of Makefiles which would need to change
to do that.
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Adding CC: cfe-dev 
> On Dec 2, 2015, at 9:56 AM, Phil Tomson via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> 0 down vote <> favorite
<http://stackoverflow.com/questions/34049511/how-to-pass-optimization-passes-to-clang#>
> I'm trying to debug an issue for a new target where a testcase fails
with -O1 optimization and passes with -O0 optimization.
> 
> I got a list of optimization passes being performed when 'clang
-O1' is called like this:
> 
> llvm-as < /dev/null | opt -O1 -disable-output -debug-pass=Arguments
> Which results in:
> 
> Pass Arguments:  -no-aa -tbaa -targetlibinfo -basicaa -notti -preverify
-domtree -verify -simplifycfg -domtree -sroa -early-cse -lower-expect
> Pass Arguments:  -targetlibinfo -no-aa -tbaa -basicaa -notti -globalopt
-ipsccp -deadargelim -instcombine -simplifycfg -basiccg -prune-eh -inline-cost
-always-inline -functionattrs -sroa -domtree -early-cse -simplify-libcalls
-lazy-value-info -jump-threading -correlated-propagation -simplifycfg
-instcombine -tailcallelim -simplifycfg -reassociate -domtree -loops
-loop-simplify -lcssa -loop-rotate -licm -lcssa -loop-unswitch -instcombine
-scalar-evolution -loop-simplify -lcssa -indvars -loop-idiom -loop-deletion
-loop-unroll -memdep -memcpyopt -sccp -instcombine -lazy-value-info
-jump-threading -correlated-propagation -domtree -memdep -dse -adce -simplifycfg
-instcombine -strip-dead-prototypes -preverify -domtree -verify
> 
> (BTW: why are there two Pass Arguments lists returned there?)
> 
This is because the middle-end and the backend are using a different PassManager
(I don’t think there is any reason for doing this but that’s how it’s
implemented in clang).
> Now my intent is to figure out which optimization pass is causing the
problem by trying each one until I hit the same problem as with -O1, but clang
itself doesn't seem to allow these commandline options, for example:
> 
> clang -loops -lcssa ....
> Results in:
> 
> clang: warning: -loops: 'linker' input unused
> clang: warning: -lcssa: 'linker' input unused
> 
> 
> (Makes sense as it conflicts with the -l command line opt) 
> So is there a way to pass these in on the command line? (or bonus if 
> there's a way to specify a file which contains a list of optimization 
> passes to perform)
> 
> Note: I realize there must be a way to break everything up into stages and
use opt at some point and pass the optimization command line options to it, but
I've got a pretty large set of Makefiles which would need to change to do
that.
> 
> 
There is no way that I know of (but modifying the PassManagerBuilder and
rebuilding clang). But you may start by bisecting the input files compiling half
of them with O1 and the other half with O0 and recurse till you find the file
that is miscompiled with O1. Then you can use opt to test variant of the
pipeline on this file and relink manually.

— 
Mehdi
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On 2 Dec 2015, at 17:56, Phil Tomson via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Now my intent is to figure out which optimization pass is causing the
problem by trying each one until I hit the same problem as with -O1, but clang
itself doesn't seem to allow these commandline options, for example:
> 
> clang -loops -lcssa ....
> 
> 
If you want to pass LLVM arguments to clang, then you must prefix them with
-llvm (e.g. -mllvm -loops -mllvm lcssa).

David

On Wed, Dec 2, 2015 at 10:17 AM, David Chisnall <David.Chisnall at
cl.cam.ac.uk
> wrote:
> On 2 Dec 2015, at 17:56, Phil Tomson via llvm-dev <llvm-dev at
lists.llvm.org>
> wrote:
> >
> > Now my intent is to figure out which optimization pass is causing the
> problem by trying each one until I hit the same problem as with -O1, but
> clang itself doesn't seem to allow these commandline options, for
example:
> >
> > clang -loops -lcssa ....
> >
> >
>
> If you want to pass LLVM arguments to clang, then you must prefix them
> with -llvm (e.g. -mllvm -loops -mllvm lcssa).
>
>
I just tried this:
CFLAGS += -mllvm adce -mllvm loops -mllvm loop-simplify -mllvm lcssa -mllvm
simplify-libcalls

And get:

clang (LLVM option parsing): Unknown command line argument 'adce'.  Try:
'clang (LLVM option parsing) -help'
clang (LLVM option parsing): Unknown command line argument 'loops'. 
Try:
'clang (LLVM option parsing) -help'
clang (LLVM option parsing): Unknown command line argument
'loop-simplify'.  Try: 'clang (LLVM option parsing) -help'
clang (LLVM option parsing): Unknown command line argument 'lcssa'. 
Try:
'clang (LLVM option parsing) -help'
clang (LLVM option parsing): Unknown command line argument
'simplify-libcalls'.  Try: 'clang (LLVM option parsing) -help'


> David
>
>
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On 12/02/15 11:56, Phil Tomson via llvm-dev wrote:
> Note: I realize there must be a way to break everything up into stages
> and use /opt/ at some point and pass the optimization command line
> options to it, but I've got a pretty large set of Makefiles which would
> need to change to do that.
Using opt is the way to go.

For your Makefile issue write your own "clang" script that is ahead of
the real clang.  Have it run clang/opt/llc for you and then you can 
easily change the optimization phases for opt.
-- 

-Bill Seurer

On Wed, Dec 02, 2015 at 12:42:44PM -0600, Bill Seurer via llvm-dev
wrote:
> On 12/02/15 11:56, Phil Tomson via llvm-dev wrote:
> >Note: I realize there must be a way to break everything up into stages
> >and use /opt/ at some point and pass the optimization command line
> >options to it, but I've got a pretty large set of Makefiles which
would
> >need to change to do that.
> 
> Using opt is the way to go.
> 
> For your Makefile issue write your own "clang" script that is
ahead of the
> real clang.  Have it run clang/opt/llc for you and then you can easily
> change the optimization phases for opt.
If you're planning to call your own passes, you can also register them
for clang use, as described in the tutorial we gave at LLVM DEV 2015.
See for instance:

   
https://github.com/quarkslab/llvm-dev-meeting-tutorial-2015/blob/master/MBA/MBA.cpp#L157