[Bug tree-optimization/86071] New: -O0 -foptimize-sibling-calls doesn't optimize

[Hi-Angel at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86071

            Bug ID: 86071
           Summary: -O0 -foptimize-sibling-calls doesn't optimize
           Product: gcc
           Version: 8.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Hi-Angel at yandex dot ru
  Target Milestone: ---

# Steps to reproduce:

        $ cat test.cpp                                           
        struct Node {
                Node* children;
        };

        const Node& descend(const Node& node) {
                if (!node.children) {
                        return node;
                } else // not a leaf
                        return descend(*node.children);
        }

        int main() {
                Node end;
                Node ring = Node{new Node{&end}};
                end.children = ˚
                descend(ring);
        }
        $ g++ test.cpp -o a -O0 -g3 -foptimize-sibling-calls
        $ ./a
        [1]    21291 segmentation fault (core dumped)  ./a

Running under gdb shows that crash is because of exhausted stack, i.e.
tail-recursion optimization didn't work.


# Additional information

This one testcase actually does work upon replacing -O0 with -O3.

However, I also have a bit bigger testcase, where tail-recursion optimization
doesn't work even with -O3. I wonder, if it's worth a separate bug.