[LLVMdev] Operations on constant array value?

[James Williams]

2010/1/11 Garrison Venn <gvenn.cfe.dev at gmail.com>

> Sorry to keep this thread alive, but I'm learning so ...
>
> There is more. The doc for GlobalValue::LinkageTypes or the C API
> LLVMLinkage is not as clear as the
> lang ref manual. See: http://llvm.org/docs/LangRef.html#linkage. I'm
> pointing this out because something
> like LinkerPrivateLinkage (LLVMLinkerPrivateLinkage), or another one, might
> be more appropriate to
> your throw away use case (if I understand your use correctly). One should
> test this of course, and/or one
> of the experts could chime in hint hint. :-)
>

I think I'd understand the LLVM linkage document better if I had more
knowledge of ELF - I suspect there's a close correspondance between LLVM
linkage types and corresponding features in ELF but I could be confused
here.

I also found the documentation on derived types less clear in places. I
might have missed it but I don't think it's made explicit what operations
are allowed on derived types (actually none?)

Otherwise the LLVM documentation is generally very good and this together
with the clear and orthogonal nature of the IR has enabled me to make huge
progress towards replacing my compiler's back end with LLVM in a couple of
weekends and a few evenings.

-- James


Anyway thought this info. might be useful, however rehashed.
>
> Garrison
>
> On Jan 11, 2010, at 16:34, James Williams wrote:
>
> 2010/1/11 Garrison Venn <gvenn.cfe.dev at gmail.com>
>
>> I have not tried this, but a linkage type of PrivateLinkage would not add
>> to the symbol table according
>> to the doc.
>>
>> LLVMSetLinkage(g, LLVMPrivateLinkage);
>>
>
> Thanks - I hadn't thought of that.
>
>>
>> Garrison
>>
>> On Jan 11, 2010, at 14:03, James Williams wrote:
>>
>> 2010/1/11 Eli Friedman <eli.friedman at gmail.com>
>>
>>> On Mon, Jan 11, 2010 at 7:07 AM, James Williams <junk at giantblob.com>
>>> wrote:
>>> > Hi,
>>> >
>>> > I've read http://llvm.org/docs/LangRef.html#t_array and
>>> > http://llvm.org/docs/GetElementPtr.html and if I've understood right
>>> there
>>> > are no operations that act directly on arrays - instead I need to use
>>> > getelementptr on a pointer to an array to get a pointer to an array
>>> element.
>>> > I also understand that there is no 'address of' operation.
>>> >
>>> > As a result I can't figure out how to use constant derived types
>>> without
>>> > assigning them to a global. Say I want to use the C bindings function
>>> > LLVMValueRef LLVMConstString(char *, int, int) to get an int8* pointer
>>> to a
>>> > C string constant - there doesn't seem to be any way to directly use
>>> the
>>> > resulting [N x i8] value directly and there's no operator that gives me
>>> its
>>> > address.
>>> >
>>> snip
>>>
>>> >
>>> > Is it possible to get the address of an element of a constant array or
>>> > struct without first initializing a global variable to the constant?
>>>
>>> No.
>>>
>>
>> OK. I'd have preferred to have to avoid bloating the module symbol table
>> with global symbols that will never be referenced but it's no big deal.
>>
>>>
>>> -Eli
>>>
>>>
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>
>
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