Declaring variables for intermediate calculations and performance

I have a program that runs billions of calculations and I'm trying to get it to run faster. In my program, I declare a lot of variables for intermediate calculations. For example, in pseudo code:

public bool FunctionThatGetsCalledInMain(manyparameters)
{
    for (int i = 0; i < 10000000; i++)
    {
        int x = bigFunctionThatReturnsAnInt(manyparameters)
        double y = bigFunctionThatReturnsADouble(manyparameters)
        string z = bigFunctionThatReturnsAString(manyparameters)

        bool b = someFunctionOfXYZ(x,y,z)
    }
}

I'm wondering if I can improve performance by doing something like:

public bool FunctionThatGetsCalledInMain(manyparameters)
{
    for (int i = 0; i < 10000000; i++)
    {
        bool b = someFunctionOfXYZ(bigFunctionThatReturnsAnInt(manyparameters),bigFunctionThatReturnsADouble(manyparameters),bigFunctionThatReturnsAString(manyparameters))
    }
}

I know it looks horrendous, but I really need to cut the time. Not sure if this theoretically makes a difference at all.