llvm dev - May 2012 - [LLVMdev] CloneFunctionInto() overwrites alignment attribute

Hi everybody,

I am trying to clone a function body into an existing declaration.
That declaration has the same number of parameters but they differ in 
type and alignment.
Fortunately, it does not care about the type.
Unfortunately, CloneFunctionInto() copies the attributes from the old 
function to the new one unconditionally, overwriting the alignment 
attribute.
Also, the Attribute interface does not allow me to change the alignment 
of a parameter afterwards ("Attempt to change alignment!" assertion). 
Removing the attribute and setting it again is also not allowed.

Note that I don't want to exclude the arguments from cloning (not adding 
them to the ValueMap) since the main point of using CloneFunctionInto() 
is that I don't have to manually rewire them.

I think it is generally not a good idea to just blindly copy and 
overwrite all attributes (including function attributes) since it might 
more often be the case that CloneFunctionInto() is used exactly to copy 
some code into a different signature.

Any ideas?
I am willing to submit a trivial patch that allows to control this 
behavior via a parameter to CloneFunctionInto() with a default value 
that does not change the current behavior.

Cheers,
Ralf

Short update:

It is possible to get around the problem by the following workaround:

1) create a temporary function declaration tmpF
2) tmpF->setAttributes(targetF->getAttributes)
3) CloneFunctionInto(targetF, sourceF, ...)
4) targetF->copyAttributesFrom(tmpF)
5) delete tmpF

Storing the attributes of the target and calling setAttributes() after 
cloning does not work, apparently setAttributes() silently ignores 
alignments.

Cheers,
Ralf

On 5/15/12 6:18 PM, Ralf Karrenberg wrote:
> Hi everybody,
>
> I am trying to clone a function body into an existing declaration.
> That declaration has the same number of parameters but they differ in
> type and alignment.
> Fortunately, it does not care about the type.
> Unfortunately, CloneFunctionInto() copies the attributes from the old
> function to the new one unconditionally, overwriting the alignment
> attribute.
> Also, the Attribute interface does not allow me to change the alignment
> of a parameter afterwards ("Attempt to change alignment!"
assertion).
> Removing the attribute and setting it again is also not allowed.
>
> Note that I don't want to exclude the arguments from cloning (not
adding
> them to the ValueMap) since the main point of using CloneFunctionInto()
> is that I don't have to manually rewire them.
>
> I think it is generally not a good idea to just blindly copy and
> overwrite all attributes (including function attributes) since it might
> more often be the case that CloneFunctionInto() is used exactly to copy
> some code into a different signature.
>
> Any ideas?
> I am willing to submit a trivial patch that allows to control this
> behavior via a parameter to CloneFunctionInto() with a default value
> that does not change the current behavior.
>
> Cheers,
> Ralf
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