[Issue 21121] Optimizer slowdowns

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21121
Issue 21121 depends on issue 6401, which changed state.

Issue 6401 Summary: infinite loop with -inline in gflow.c:accumaecpx
https://issues.dlang.org/show_bug.cgi?id=6401

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

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