[Issue 19550] [REG 2.078] Massive compiler backend slowdown

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19550

--- Comment #6 from safety0ff.bugz <safety0ff.bugz at gmail.com> ---
Ok I believe to have found the culprit:
There is a special case for OPcomma here, which traverses the entire list of
elems:
https://github.com/dlang/dmd/blob/793635ea7ad3cf30c02bf1b5d51eefdc166c8b82/src/dmd/backend/gflow.d#L624

But `accumaecpx`already recurses over the list of elems:
https://github.com/dlang/dmd/blob/793635ea7ad3cf30c02bf1b5d51eefdc166c8b82/src/dmd/backend/gflow.d#L1102
at `accumaecpx(n.EV.E2);`

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