[LLVMdev] problem with replacing an instruction

[Frank Winter]

I am trying to change this

define void @main(float* noalias %arg0, float* noalias %arg1, float* 
noalias %arg2) {
entrypoint:
   %0 = bitcast float* %arg1 to <4 x float>*

intothis

define void @main(float* noalias %arg0, float* noalias %arg1, float* 
noalias %arg2) {
entrypoint:
   %0 = getelementptr float* %arg1, i64 0
   %1 = bitcast float* %0 to <4 x float>*


I must be close but the final instruction replacement results in a segfault.


   for (Instruction& I : BB) {
     if (isa<BitCastInst>(I)) {
       BitCastInst* BCI = dyn_cast<BitCastInst>(&I);
       for (Use& U : I.operands()) {
           Value* V = U.get();
           if (!dyn_cast<Instruction>(V)) {
             // must be a function's argument
             std::vector<llvm::Value*> vect_1;
             vect_1.push_back(Builder->getInt64(0));
             llvm::GetElementPtrInst* gep1 = 
llvm::GetElementPtrInst::Create(V, ArrayRef< Value * >(vect_1) );
             BB.getInstList().insert(&I, gep1);

             llvm::BitCastInst *bci = new BitCastInst (gep1, 
BCI->getDestTy() );
             llvm::ReplaceInstWithInst( &I , bci );
           }
        }
     }
  }

What am I missing?

Thanks,
Frank