Find values in a basicblock,which are computed in previous basicblocks - llvm

Question

In a basicblock I wants to find all the values used in instructions, That are not computed in the same basicblock.
Example,
for.body5:
%i.015 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.body ]
%add1 = add nsw i32 %2, %i.015
%arrayidx = getelementptr inbounds [100 x i32]* %b, i32 0, i32 %i.015
store i32 %add1, i32* %arrayidx, align 4, !tbaa !0
%arrayidx2 = getelementptr inbounds [100 x i32]* %a, i32 0, i32 %i.015
store i32 %add1, i32* %arrayidx2, align 4, !tbaa !0
%inc = add nsw i32 %i.015, 1
%cmp = icmp slt i32 %inc, %3
br i1 %cmp, label %for.body, label %for.cond3.preheader
In above example i should get,
%2
%b
%a
%3
Which are declared and/or assigned in other basicblocks.
Please Suggest me a method.
Thanks in advance.

Answer 1

Hi I havent tested this out, but I would do something like this:
vector<Value*> values;
BasicBlock::iterator it;
User::op_iterator it;
// Iterate over all of the instructions in the Block
for (it=block->begin(); it++; it != block->end()){
// Iterate over the operands used by an instruction. 'op_begin' Defined in llvm::User class.
for (operand_it=it->op_begin(); operand_it++; operand_it != it->op_end() ){
// Could this if else statement be reduced?
// If this operand is an argument it was not defined in the block.
if (isa<Argument>(operand_it)){
values.push_back(operand_it);
}
// Otherwize, it could be a constant value or ...
else if (!isa<Instruction>(operand_it)){
continue;
}
// Check if the parent of the instruction is not the block in question.
else if (((Instruction*)operand_it)->getParent() != block){
values.push_back(operand_it);
}
}
}