[LLVMdev] How to create global string array? (user question)

[o.j.sivart at gmail.com]

I have found an invaluable way to find an answer (not necessarily the best answer, but an initial answer at least) is to write a simple c source file, compile it to bitcode (clang -S -emit-llvm sourcefile.c), then get llc to produce a cpp file containing the calls required to produce that bitcode (llc -march=cpp sourcefile.s). I find that the resulting source file (sourcefile.s.cpp) is usually enough to make an initial start on figuring out how to do what I want if I can't otherwise find it in the docs.

In your case sourcefile.c would simply be:
const char* ss[] = {"s1","s2"};

On 02/06/2010, at 5:04 AM, Yuri wrote:

> I am trying to create such module with API (it's equivalent to c++: 
> const char* ss[] = {"s1","s2"};):
> 
> @ss = global [2 x i8*] [i8* getelementptr inbounds ([3 x i8]* @.str1, 
> i32 0, i32 0), i8* getelementptr inbounds ([3 x i8]* @.str2, i32 0, i32 
> 0)] ; <[2 x i8*]*> [#uses=0]
> @.str1 = private constant [3 x i8] c"s1\00", align 1 ; <[3 x i8]*> [#uses=1]
> @.str2 = private constant [3 x i8] c"s2\00", align 1 ; <[3 x i8]*> [#uses=1]
> 
> Code below doesn't compile because to initialize GlobalVariable I need 
> ConstantArray*, ConstantArray::get requires vector<Constant*>, but 
> getelementptr is an instruction and it's not Constant*, but Value*.
> 
> What is the correct way to create such module? It's really tye
> 
> Yuri
> 
> --- c++ code ---
> #include "llvm/LLVMContext.h"
> #include "llvm/Module.h"
> #include "llvm/DerivedTypes.h"
> #include "llvm/Constants.h"
> #include "llvm/Instructions.h"
> #include "llvm/Analysis/Verifier.h"
> #include <stdio.h>
> #include <vector>
> using namespace llvm;
> using namespace std;
> 
> Constant* mk_string(Module *M, LLVMContext &Context, const string &svalue) {
>   ArrayType *Ty = ArrayType::get(Type::getInt8Ty(Context),svalue.size()+1);
>   GlobalVariable *GV = new llvm::GlobalVariable(
>     *M,
>     Ty,
>     true,
>     GlobalValue::InternalLinkage,
>     ConstantArray::get(Context,svalue),
>     "str",
>     0,
>     false,
>     0);
> 
>   vector<Constant*> idxs;
>   idxs.push_back(ConstantInt::get(Type::getInt32Ty(Context), 0, false));
>   idxs.push_back(ConstantInt::get(Type::getInt32Ty(Context), 0, false));
>   return (GetElementPtrInst::Create(
>     GV,
>     idxs.begin(),
>     idxs.end(),
>     "gepi",
>     (BasicBlock*)0
>   ));
> }
> 
> main() {
>   LLVMContext Context;
>   Module *M = new Module("test", Context);
>   //
>   vector<Constant*> strs;
>   strs.push_back(mk_string(M, Context, "s1"));
>   strs.push_back(mk_string(M, Context, "s2"));
>   ArrayType *Ty = 
> ArrayType::get(Type::getInt8Ty(Context)->getPointerTo(),2);
>   new llvm::GlobalVariable(
>     *M,
>     Ty,
>     true,
>     GlobalValue::InternalLinkage,
>     ConstantArray::get(Ty,strs),
>     "ss",
>     0,
>     false,
>     0);
>   verifyModule(*M);
>   delete M;
> }
> 
> 
> 
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