not able to evaluate SSA R code

[clarkfitzg]

How can the following code be converted to SSA?

library(rstatic)

node0 = quote_ast({
    x = data.frame(a = 1:10, b = letters[1:10])
    x$c = rnorm(10)
    sum(x$a)
    head(x)
})

# We can evaluate this.
eval(to_r(node0))

# Seems to go from a brace to a function
node = to_cfg(node0)
nr = to_r(node)
f = eval(nr)

# But we can't evaluate it here.
f()

Some relevant output:

> f()
Error in x_2$c = rnorm(10) : object 'x_2' not found
> f
function () 
{
    x_1 = data.frame(a = 1:10, b = letters[1:10])
    x_2$c = rnorm(10)
    sum(x_2$a)
    return(head(x_2))
}

It seems we need to add the line x_2 = x_1.