Recursive functions cause arg/lookup to return edges that point to nodes that don't exist

[FeldrinH]

In some cases recursive functions cause arg/lookup to return nodes that have edges to ARG nodes that don't exist.

Reproduction:

// recursion.c
int fib(int n) {
    if (n < 2) {
        return 1;
    }
    return fib(n - 1) + fib(n - 2);
}

int main() {
    int a;
    fib(a);
}

// goblint.json
{
  "files": ["recursion.c"]
}

{"jsonrpc":"2.0","id":"20","method":"arg/lookup","params":{"node":"fun1620fib(18)[15]"}}

returns

{"id":"20","jsonrpc":"2.0","result":[{"node":"fun1620fib(18)[15]","cfg_node":"fun1620","context":"18","path":"15","location":{"file":"recursion.c","line":1,"column":1,"byte":136,"endLine":6,"endColumn":1,"endByte":230},"function":"fib","next":[{"edge":{"cfg":{"string":"(body)","type":"entry","function":"fib"}},"node":"s77(18)[20]","cfg_node":"77","context":"18","path":"20","location":{"file":"recursion.c","line":2,"column":9,"byte":161,"endLine":2,"endColumn":14,"endByte":166},"function":"fib"}],"prev":[{"edge":{"entry":{"lval":null,"function":"fib","args":["a"]}},"node":"s84(9)[11]","cfg_node":"84","context":"9","path":"11","location":{"file":"recursion.c","line":10,"column":5,"byte":261,"endLine":10,"endColumn":11,"endByte":267},"function":"main"},{"edge":{"entry":{"lval":"tmp___0","function":"fib","args":["n - 2"]}},"node":"s81(18)[61]","cfg_node":"81","context":"18","path":"61","location":{"file":"recursion.c","line":5,"column":5,"byte":198,"endLine":5,"endColumn":35,"endByte":228},"function":"fib"},{"edge":{"entry":{"lval":"tmp___0","function":"fib","args":["n - 2"]}},"node":"s81(18)[38]","cfg_node":"81","context":"18","path":"38","location":{"file":"recursion.c","line":5,"column":5,"byte":198,"endLine":5,"endColumn":35,"endByte":228},"function":"fib"},{"edge":{"entry":{"lval":"tmp___0","function":"fib","args":["n - 2"]}},"node":"s81(18)[27]","cfg_node":"81","context":"18","path":"27","location":{"file":"recursion.c","line":5,"column":5,"byte":198,"endLine":5,"endColumn":35,"endByte":228},"function":"fib"},{"edge":{"entry":{"lval":"tmp","function":"fib","args":["n - 1"]}},"node":"s80(18)[27]","cfg_node":"80","context":"18","path":"27","location":{"file":"recursion.c","line":5,"column":5,"byte":198,"endLine":5,"endColumn":35,"endByte":228},"function":"fib"}]}]}

Where the node s81(18)[61] does not exist according to both arg/lookup and arg/dot.

The issue seems to occur when analyzing with reset=true as well as reset=false.

Tested on Goblint version heads/master-0-g9daa89f52.