[LLVMdev] Operations on constant array value?

James Williams junk at giantblob.com
Mon Jan 11 07:07:32 PST 2010


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

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 + 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?

Thanks in advance,
-- James Williams
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