[LLVMdev] Function calls only being JIT'd once by Kaleidoscope with MCJIT?

[Lang Hames]

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.
>
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