[Bug c++/108162] New: Missed optimization opportunity. Complex function that starts with if (param == 0) return 0;

[levo.delellis at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108162

            Bug ID: 108162
           Summary: Missed optimization opportunity. Complex function that
                    starts with if (param == 0) return 0;
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: levo.delellis at gmail dot com
  Target Milestone: ---

I had a lot of fun writing https://bolinlang.com/does-it-inline

I was intentionally trying to break the optimizer. I found a few cases in clang
and two cases I don't think should apply but I think both can gain from the
last one. Skipping a function call when the function starts with `if (param ==
0) return 0;`. I tested with a recursive fibonacci. If you scroll to the very
bottom you'll see it.

Cases that clang optimizes but gcc did not A) Round 3 a and b. I don't think
locale will affect it and clang optimizes it. All of round 4 clang optimizes. I
suspect there's something getting in the way of peeking through push and size.
I vaguely remember thinking std::forward may get in the way in the past but it
was long enough ago that I don't remember what I was doing to think that