How to resolve AllocaInst from the value that was the result of LoadInst in LLVM?

Question

Conceptually, what I would like to do is quite simple. I use the Alloca method described in the Kaleidoscope example paired with mem2reg to reduce the need to manually create Phi nodes.

I implemented several aspects of my custom language, but I had a problem with implementing post increment / decment in a general way.

My AST node PostIncrDecrNodecontains a token denoting ++or --, and an AST node expression that is encoded to return llvm::Value*, like the Kaleidoscope example. I already noticed that I probably would need to return something else, and then llvm::Value*, since my language is very type safe, and I need to know things like signature of integral types, but now I feel that I can also need to track llvm::AllocaInst.

A simple example of a situation is this code:

int myfunction(int i)
{
    return i++;
}

My AST print debugging is as follows:

- CompilationUnit:test.str
    - FunctionDeclarationNode
        - IdentifierNode:int
        - IdentifierNode:myfunction
        - FunctionParameterNode
            - IdentifierNode:int
            - IdentifierNode:i
        - BlockNode
            - ReturnNode
                - PostIncrDecrNode
                    - IdentifierNode:i

The last two lines are an important part here, since I have PostIncrDecrNodeone that contains IdentifierNode, which will be encoded as follows:

Value* IdentifierNode::codeGenInternal(CodeGenContext& context)
{
    Value* rtn = NULL;
    SharedSymbolEntry entry = context.getSymbolInScopeByName(*value);
    Value* val = entry ? entry->llvmVal : NULL;
    if(val)
    {
        IRBuilder<>* builder = context.getIRBuilder();
        rtn = builder->CreateLoad(val, value->c_str());
    }
    else
    {
        context.handleCodeGenError(*this, "Unknown variable name: " + Twine(value->c_str()));

    }
    return rtn;
}

SharedSymbolEntry entry = context.getSymbolInScopeByName(*value); shared_ptr to std::String ' IdentifierNode ( ) SharedSymbolEntry ( , llvm::Value*, llvm::AllocaInst*) , AST.

, PostIncrDecrNode alloca, llvm::Value* rtn = builder->CreateLoad(val, value->c_str());.

LLVM llvm::AllocaInst* llvm::Value*, ( , )?

, , . , , , .

• llvm-dependencies-alloca-load
• llvm-pass-how-to-insert-a-variable-using-existing-variable-value
• get-pointer-to-llvmvalue-previously-allocated-for-createload-function

Answer 1

llvm::Value* ( LoadInst*), LoadInst* llvm:Value* llvm::LoadInst* llvm::LoadInst* LLVM :

Value* val = someFunction(...); 
if (llvm::LoadInst* I = dyn_cast<llvm::LoadInst>(val)
{
     // do something with the load instruction I
}
else // not a load instruction

llvm::LoadInst* , , getPointerOperand(). AllocaInst* . , AllocaInst, AllocaInst, - (, GetElementPtrInst).