[LLVMdev] Operations on constant array value?

[James Williams]

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.
>> >
>> > The only way I can see to get a pointer to the string constant array is
>> to
>> > go through a global variable, for example:
>> >
>> > g = LLVMAddGlobal(module, LLVMTypeOf(v), "__string_" +
>> > string_literal_number);
>> > string_literal_number = string_literal_number + 1;
>> > v = LLVMConstString(string_literal, string_literal.Length, 0);
>> > LLVMSetInitializer(g, v);
>> > elements = { LLVMConstInt(LLVMInt32Type(), 0L, 0),
>> > LLVMConstInt(LLVMInt32Type(), 0L, 0) };
>> > return LLVMConstInBoundsGEP(g, elements, 2);
>> >
>> > 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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