llvm dev - Dec 2014 - [LLVMdev] Function calls only being JIT'd once by Kaleidoscope with MCJIT?

Hi all,

Starting from Chapter 4 of the Kaleidoscope tutorial (where the JIT
support is added), there's some strange behaviour,

ready> def foo(x y) x+y;
ready> Read function definition:
define double @foo(double %x, double %y) {
entry:
  %addtmp = fadd double %x, %y
  ret double %addtmp
}

ready> foo(1, 2);
ready> Evaluated to 3.000000
ready> foo(3, 4);
ready> Evaluated to 3.000000

You can see that foo(3, 4) is not being computed correctly. Well
actually, it appears to not be getting compiled. It seems like the
Kaleidoscope tutorial has slipped a bit with the recent JIT changes in
LLVM.

I have attached a patch which gets the above working. I found a blog
post about getting Kaleidoscope working with MCJIT
(http://blog.llvm.org/2013/07/using-mcjit-with-kaleidoscope-tutorial.html)
which most of the code comes from. Unfortunately that didn't
completely work, it was using a deprecated API
"RTDyldMemoryManager::getPointerToNamedFunction" which was failing to
find function symbols for reasons I didn't have time to track down. I
changed it to use the recommended getSymbolAddress, and now it works.

If the attached seems reasonable, there's more to do,

  * Updating the Kaleidoscope tutorial to explain all this. Andy
Kaylor's blog post [1] is good place to start. There are other methods
of using MCJIT in Kaleidoscope explained on that blog, but the
attached method is perhaps the most straightforward one.
  * Update all future chapter code to fix this bug.
  * Updating the Kaleidoscope/MCJIT example code. This code doesn't
get built when you request examples to be built, so it has suffered
bit rot (doesn't compile at the moment, I have local patches for this
but can submit those in the future). Should we be building this code
more regularly?
  * .... Bonus: Add unit tests to Kaleidoscope so it doesn't slip like
this in the future?

Am I on the right track with these fixes? If so I'll try and get to
the points above, or at least raise a PR for it. Maybe in the meantime
a note should be added to the tutorial that this is a known bug?

Thanks for your time!
Charlie.
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Hi Charlie,

Thanks for working on this. Sorry it took me so long to get around to
looking at it.

I've just tested the patch out on Top-of-tree and I see:

ready> def foo(x y) x+y;
ready> Read function definition:
define double @foo(double %x, double %y) {
entry:
  %addtmp = fadd double %x, %y
  ret double %addtmp
}

ready> foo(1,2);
ready> Evaluated to 3.000000
ready> foo(3,4);
ready> LLVM ERROR: Program used extern function '_foo' which could
not be
resolved!

Have you seen the same thing? If not, can you describe your system config
and I'll dig in and try to see what's causing this to behave differently
for me.

- Lang.

On Fri, Dec 26, 2014 at 9:09 AM, Charlie Turner <charlesturner7c5 at
gmail.com>
wrote:
> Hi all,
>
> Starting from Chapter 4 of the Kaleidoscope tutorial (where the JIT
> support is added), there's some strange behaviour,
>
> ready> def foo(x y) x+y;
> ready> Read function definition:
> define double @foo(double %x, double %y) {
> entry:
>   %addtmp = fadd double %x, %y
>   ret double %addtmp
> }
>
> ready> foo(1, 2);
> ready> Evaluated to 3.000000
> ready> foo(3, 4);
> ready> Evaluated to 3.000000
>
> You can see that foo(3, 4) is not being computed correctly. Well
> actually, it appears to not be getting compiled. It seems like the
> Kaleidoscope tutorial has slipped a bit with the recent JIT changes in
> LLVM.
>
> I have attached a patch which gets the above working. I found a blog
> post about getting Kaleidoscope working with MCJIT
> (http://blog.llvm.org/2013/07/using-mcjit-with-kaleidoscope-tutorial.html)
> which most of the code comes from. Unfortunately that didn't
> completely work, it was using a deprecated API
> "RTDyldMemoryManager::getPointerToNamedFunction" which was
failing to
> find function symbols for reasons I didn't have time to track down. I
> changed it to use the recommended getSymbolAddress, and now it works.
>
> If the attached seems reasonable, there's more to do,
>
>   * Updating the Kaleidoscope tutorial to explain all this. Andy
> Kaylor's blog post [1] is good place to start. There are other methods
> of using MCJIT in Kaleidoscope explained on that blog, but the
> attached method is perhaps the most straightforward one.
>   * Update all future chapter code to fix this bug.
>   * Updating the Kaleidoscope/MCJIT example code. This code doesn't
> get built when you request examples to be built, so it has suffered
> bit rot (doesn't compile at the moment, I have local patches for this
> but can submit those in the future). Should we be building this code
> more regularly?
>   * .... Bonus: Add unit tests to Kaleidoscope so it doesn't slip like
> this in the future?
>
> Am I on the right track with these fixes? If so I'll try and get to
> the points above, or at least raise a PR for it. Maybe in the meantime
> a note should be added to the tutorial that this is a known bug?
>
> Thanks for your time!
> Charlie.
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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Oh - I know what this is. You were running this on Linux, right?

On MacOS I think the symbol is getting double mangled while going through
MCJIT::getSymbolAddress, hence the failure: The IR level foo function gets
compiled to "_foo" in the object file, and then "_foo" gets
mangled to
"__foo" when we look it up. Linux doesn't do assembly level
name-mangling,
so this bug doesn't show up there.

Since applying this fixes Linux, and leaves MacOS no more broken than
before, I'll put it in. Hopefully I can figure out a fix for MacOS soon.

Thanks again Charlie.

- Lang.


On Thu, Jan 15, 2015 at 4:34 PM, Lang Hames <lhames at gmail.com> wrote:
> Hi Charlie,
>
> Thanks for working on this. Sorry it took me so long to get around to
> looking at it.
>
> I've just tested the patch out on Top-of-tree and I see:
>
> ready> def foo(x y) x+y;
> ready> Read function definition:
> define double @foo(double %x, double %y) {
> entry:
>   %addtmp = fadd double %x, %y
>   ret double %addtmp
> }
>
> ready> foo(1,2);
> ready> Evaluated to 3.000000
> ready> foo(3,4);
> ready> LLVM ERROR: Program used extern function '_foo' which
could not be
> resolved!
>
> Have you seen the same thing? If not, can you describe your system config
> and I'll dig in and try to see what's causing this to behave
differently
> for me.
>
> - Lang.
>
> On Fri, Dec 26, 2014 at 9:09 AM, Charlie Turner <
> charlesturner7c5 at gmail.com> wrote:
>
>> Hi all,
>>
>> Starting from Chapter 4 of the Kaleidoscope tutorial (where the JIT
>> support is added), there's some strange behaviour,
>>
>> ready> def foo(x y) x+y;
>> ready> Read function definition:
>> define double @foo(double %x, double %y) {
>> entry:
>>   %addtmp = fadd double %x, %y
>>   ret double %addtmp
>> }
>>
>> ready> foo(1, 2);
>> ready> Evaluated to 3.000000
>> ready> foo(3, 4);
>> ready> Evaluated to 3.000000
>>
>> You can see that foo(3, 4) is not being computed correctly. Well
>> actually, it appears to not be getting compiled. It seems like the
>> Kaleidoscope tutorial has slipped a bit with the recent JIT changes in
>> LLVM.
>>
>> I have attached a patch which gets the above working. I found a blog
>> post about getting Kaleidoscope working with MCJIT
>>
(http://blog.llvm.org/2013/07/using-mcjit-with-kaleidoscope-tutorial.html
>> )
>> which most of the code comes from. Unfortunately that didn't
>> completely work, it was using a deprecated API
>> "RTDyldMemoryManager::getPointerToNamedFunction" which was
failing to
>> find function symbols for reasons I didn't have time to track down.
I
>> changed it to use the recommended getSymbolAddress, and now it works.
>>
>> If the attached seems reasonable, there's more to do,
>>
>>   * Updating the Kaleidoscope tutorial to explain all this. Andy
>> Kaylor's blog post [1] is good place to start. There are other
methods
>> of using MCJIT in Kaleidoscope explained on that blog, but the
>> attached method is perhaps the most straightforward one.
>>   * Update all future chapter code to fix this bug.
>>   * Updating the Kaleidoscope/MCJIT example code. This code doesn't
>> get built when you request examples to be built, so it has suffered
>> bit rot (doesn't compile at the moment, I have local patches for
this
>> but can submit those in the future). Should we be building this code
>> more regularly?
>>   * .... Bonus: Add unit tests to Kaleidoscope so it doesn't slip
like
>> this in the future?
>>
>> Am I on the right track with these fixes? If so I'll try and get to
>> the points above, or at least raise a PR for it. Maybe in the meantime
>> a note should be added to the tutorial that this is a known bug?
>>
>> Thanks for your time!
>> Charlie.
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
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