llvm dev - Jul 2014 - [LLVMdev] Preventing IR instruction duplication

Hi,

For a certain type of analysis I generate inline assembly which I insert
into the LLVM IR code. This
inline assembly code contains labels that should not be duplicated. Problem
is that the tail
duplication pass duplicates code. It checks isNotDuplicatable on a machine
instruction however
there is no such a flag on an IR instruction that I could set. Is there a
way to tell in an IR pass
that code should not be duplicated?

Jan
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On Jul 17, 2014, at 8:41 AM, Jan Hoogerbrugge <jan.hoogerbrugge at
gmail.com> wrote:
> Hi,
> 
> For a certain type of analysis I generate inline assembly which I insert
into the LLVM IR code. This
> inline assembly code contains labels that should not be duplicated. Problem
is that the tail
> duplication pass duplicates code. It checks isNotDuplicatable on a machine
instruction however
> there is no such a flag on an IR instruction that I could set. Is there a
way to tell in an IR pass
> that code should not be duplicated?
> 
> Jan
There is the noduplicate attribute you can place on the function definition /
the asm call site which should work

-Matt

Hi Matt,

Thanks for the answer. Unfortunately it does not seem to work.

Putting the NoDuplicate on the CallInst of an inline assembly gives the
message:

   Attribute 'noduplicate' only applies to functions!

Putting the NoDuplicate on the function in which the inline assembly
resides has not effect. Also adding
the MinSize or OptimizeForSize attribute does not stop tail duplication.
Another suggestion?

Regards,
Jan.


On Thu, Jul 17, 2014 at 6:33 PM, Matt Arsenault <arsenm2 at gmail.com>
wrote:
>
> On Jul 17, 2014, at 8:41 AM, Jan Hoogerbrugge <jan.hoogerbrugge at
gmail.com>
> wrote:
>
> > Hi,
> >
> > For a certain type of analysis I generate inline assembly which I
insert
> into the LLVM IR code. This
> > inline assembly code contains labels that should not be duplicated.
> Problem is that the tail
> > duplication pass duplicates code. It checks isNotDuplicatable on a
> machine instruction however
> > there is no such a flag on an IR instruction that I could set. Is
there
> a way to tell in an IR pass
> > that code should not be duplicated?
> >
> > Jan
>
> There is the noduplicate attribute you can place on the function
> definition / the asm call site which should work
>
> -Matt
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Is this volatile inline asm?  If so, I don't think we should duplicate it.
 If we do, that might be a bug.


On Thu, Jul 17, 2014 at 8:41 AM, Jan Hoogerbrugge <
jan.hoogerbrugge at gmail.com> wrote:
> Hi,
>
> For a certain type of analysis I generate inline assembly which I insert
> into the LLVM IR code. This
> inline assembly code contains labels that should not be duplicated.
> Problem is that the tail
> duplication pass duplicates code. It checks isNotDuplicatable on a machine
> instruction however
> there is no such a flag on an IR instruction that I could set. Is there a
> way to tell in an IR pass
> that code should not be duplicated?
>
> Jan
>
> _______________________________________________
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> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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