[LLVMdev] Nested functions

[Devang Patel]

On Mar 4, 2009, at 1:33 PM, S. Bharadwaj Yadavalli wrote:

> Hi Duncan,
>
> Thanks for your reply.
>
> I did try the method suggested by you. I got a foo.bc with -emit- 
> llvm switch. llc on foo.bc gets me the same assertion failure, as  
> you pointed out.
>
> Then I ran bugpoint to generate bugpoint-reduced-simplified.bc and  
> bugpoint-reduced-function.bc. My previous experience is that if I  
> compile either if them, I would get the same failure as I did with  
> foo.bc. That is not the case. I get a different assertion failure  
> when I compile either of them with llc which is as follows:
>
> llc: <llvm-src>/llvm/lib/CodeGen/AsmPrinter/DwarfWriter.cpp:2808:  
> void llvm::DwarfDebug::ConstructCompileUnits(): Assertion `Root- 
> >hasLinkOnceLinkage() && Root->hasOneUse() && "Malformed compile  
> unit descriptor anchor type"' failed.

This is because bugpoint tool does not understand debug info intrinsics.
To avoid this, when you generate foo.bc with -emit-llvm switch, do not  
use -g on the llvm-gcc command line.

-
Devang

>
>
> This makes it hard for me to easily create a test case and submit a  
> bug report.
>
> Hence, I thought I should take this opportunity to delve deeper into  
> LLVM and look at this issue.
>
> Any further nudges / help is highly appreciated!
>
> Thanks,
>
> Bharadwaj
>
> On Wed, Mar 4, 2009 at 3:59 PM, Duncan Sands <baldrick at free.fr> wrote:
> Hi Bharadwaj,
>
> > I get the following error during compilation using the LLVM cross- 
> compiler
> > (x86_64->arm).
> >
> > error: nested functions are disabled, use -fnested-functions to re- 
> enable
>
> yes, nested functions are disabled by default in llvm-gcc (not sure  
> why -
> maybe a historical hang over from the days when they were not  
> supported?).
>
> > With -fnested-functions switch, I get the following error:
> >
> > <llvm-src-dir>/llvm/lib/Target/ARM/ARMISelLowering.cpp:1439: virtual
> > llvm::SDValue llvm::ARMTargetLowering::LowerOperation(llvm::SDValue,
> > llvm::SelectionDAG&): Assertion `0 && "Don't know how to custom  
> lower
> > this!"' failed.
> > frobos/tests/hello.c:453: internal compiler error: Aborted
> > Please submit a full bug report,
> > with preprocessed source if appropriate.
> > See <URL:http://developer.apple.com/bugreporter> for instructions.
> >
> > I'd like to investigate this but am wondering if anyone has any
> > thoughts/suggestions in this area.
>
> I don't know anything about cross-compiling, but the usual way
> to debug this kind of thing is to re-run by hand the line that
> caused this assertion, but adding -emit-llvm to the command line.
> The output will then contain LLVM bitcode.  If you are lucky,
> then running llc on the bitcode will give the same assertion
> failure.  If so, then "bugpoint --run-llc the_bit_code" should
> automatically reduce a minimal testcase.
>
> Ciao,
>
> Duncan.
>
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-
Devang



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