llvm dev - Nov 2018 - Are there any tools to reduce the IR file that caused a problem?

Hi everyone,
I want to test the passes in llvm, and I got some passes sequences that caused
the crash of opt.
Although I can use bugpoint to narrow down the source of problems, I can only
get some reduced and
simplified IR and passes to reproduce the problem. My question is how to get the
reduced IR of the original IR
file to reproduce the problem. For example,
"opt a.bc -a -b -c -d (where a, b, c and d are passes)" has a crash
problem caused by "-a -b -c -d", so we can use
bugpoint to narrow down the source of problems, thus bugpoint will tell us
"You can reproduce the problem with:
opt bugpoint-reduced-simplified.bc -c". However, for the
"bugpoint-reduced-simplified.bc", I do not know the actual wrong
points
of the original "a.bc", and the pass "-c" is good for
"a.bc", the actual wrong passes sequence is "-b -c" for
"a.bc", i.e., we need to run pass "-b" before
pass "-c" to reproduce the problem on the original IR file. 
So how to reduce the original IR and get the actual wrong passes sequence? Are
there any tools? Or there are some special tips of bugpoint
for this purpose? 
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In many cases the problem is indeed in a single pass, so finding exact 
pass is rather beneficial.

If you *really* want to stick to a particular sequence of passes you can 
feed bugpoint with a custom script
that takes IR and does what you need.
The tricky part is how to control bugpoint, since sometimes it behaves 
somewhat unobvious.
I usually use exit code 134, which for bugpoint means crash:

] cat bugpoint-custom-simple.sh
opt -do-what-you-want-here "$@"  ; run something else if needed
[[ problem reproduced ]] && echo "Problem reproduces!"
&& exit 134
exit 0
] bugpoint -compile-custom -compile-command=./bugpoint-custom-check.sh 
bad.ll

regards,
   Fedor.

On 11/11/18 9:56 AM, cszide via llvm-dev wrote:
> Hi everyone,
> I want to test the passes in llvm, and I got some passes sequences 
> that caused the crash of opt.
> Although I can use bugpoint to narrow down the source of problems, I 
> can only get some reduced and
> simplified IR and passes to reproduce the problem. My question is how 
> to get the reduced IR of the original IR
> file to reproduce the problem. For example,
> "opt a.bc -a -b -c -d (where a, b, c and d are passes)" has a
crash
> problem caused by "-a -b -c -d", so we can use
> bugpoint to narrow down the source of problems, thus bugpoint will 
> tell us "You can reproduce the problem with:
> opt bugpoint-reduced-simplified.bc -c". However, for the 
> "bugpoint-reduced-simplified.bc", I do not know the actual wrong
points
> of the original "a.bc", and the pass "-c" is good for
"a.bc", the
> actual wrong passes sequence is "-b -c" for "a.bc",
i.e., we need to
> run pass "-b" before
> pass "-c" to reproduce the problem on the original IR file.
> So how to reduce the original IR and get the actual wrong passes 
> sequence? Are there any tools? Or there are some special tips of bugpoint
> for this purpose?
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Hi Fedor,
Thanks for your suggestions! I will try it.
I agree with you that "in many cases the problem is indeed in a single
pass, so finding exact
pass is rather beneficial." Actually, in my case, bugpoint also shows that
only one pass will
cause the problem, but I can only know the wrong instructions in the
"bugpoint-reduced-simplified.bc"
file rather than the original "a.bc" file. 
For example, in my test case,  the "loop-deletion" pass will cause a
problem for "bugpoint-reduced-simplified.bc".
The output of opt (in debug mode) is:
"
While deleting: i32* %
Use still stuck around after Def is destroyed:  %161 = load i32, i32*
<badref>, align 4, !tbaa !1
....
Stack dump:
0.Program arguments: /Documents/llvm/llvm6.0/llvm-6.0.0.src/build/bin/opt 
bugpoint-reduced-simplified.bc -loop-deletion -disable-output 
1.Running pass 'Function Pass Manager' on module
'bugpoint-reduced-simplified.bc'.
2.Running pass 'Loop Pass Manager' on function '@put2bitbwtile'
3.Running pass 'Delete dead loops' on basic block
'<badref>'
Aborted (core dumped)
"
Next, I use llvm-dis to disassemble "bugpoint-reduced-simplified.bc",
and I found that the
resulted "bugpoint-reduced-simplified.ll" file only contains two load
instructions, i.e.,
"
....
%241 = load i32*, i32** undef, align 8, !tbaa !1
....
%248 = load i32, i32* %241, align 4, !tbaa !5
....
"
but from "bugpoint-reduced-simplified.ll", it is difficult to know why
there is a "i32** undef" .
"bugpoint-reduced-simplified.bc" is reduced from the IR that has been
optimized by some passes,
thus it is hard to know the actual reasons.
For my test case, only a few passes sequences that contain
"loop-deletion" pass have this problem.
In most cases, the passes sequences is good. So I think the problem is caused by
interaction among passes
that why I want to know the wrong passes sequences and to reduce the original IR
file.


Best regards,
Zhide







At 2018-11-11 21:24:16, "Fedor Sergeev via llvm-dev" <llvm-dev at
lists.llvm.org> wrote:
>In many cases the problem is indeed in a single pass, so finding exact 
>pass is rather beneficial.
>
>If you *really* want to stick to a particular sequence of passes you can 
>feed bugpoint with a custom script
>that takes IR and does what you need.
>The tricky part is how to control bugpoint, since sometimes it behaves 
>somewhat unobvious.
>I usually use exit code 134, which for bugpoint means crash:
>
>] cat bugpoint-custom-simple.sh
>opt -do-what-you-want-here "$@"  ; run something else if needed
>[[ problem reproduced ]] && echo "Problem reproduces!"
&& exit 134
>exit 0
>] bugpoint -compile-custom -compile-command=./bugpoint-custom-check.sh 
>bad.ll
>
>regards,
>   Fedor.
>
>On 11/11/18 9:56 AM, cszide via llvm-dev wrote:
>> Hi everyone,
>> I want to test the passes in llvm, and I got some passes sequences 
>> that caused the crash of opt.
>> Although I can use bugpoint to narrow down the source of problems, I 
>> can only get some reduced and
>> simplified IR and passes to reproduce the problem. My question is how 
>> to get the reduced IR of the original IR
>> file to reproduce the problem. For example,
>> "opt a.bc -a -b -c -d (where a, b, c and d are passes)" has a
crash
>> problem caused by "-a -b -c -d", so we can use
>> bugpoint to narrow down the source of problems, thus bugpoint will 
>> tell us "You can reproduce the problem with:
>> opt bugpoint-reduced-simplified.bc -c". However, for the 
>> "bugpoint-reduced-simplified.bc", I do not know the actual
wrong points
>> of the original "a.bc", and the pass "-c" is good
for "a.bc", the
>> actual wrong passes sequence is "-b -c" for "a.bc",
i.e., we need to
>> run pass "-b" before
>> pass "-c" to reproduce the problem on the original IR file.
>> So how to reduce the original IR and get the actual wrong passes 
>> sequence? Are there any tools? Or there are some special tips of
bugpoint
>> for this purpose?
>>
>>
>>
>> _______________________________________________
>> 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
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