[Issue 22372] Loop index incorrectly optimised out for -release -O

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22372

Teodor Dutu <teodor.dutu at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |teodor.dutu at gmail.com
           Severity|regression                  |blocker

--- Comment #1 from Teodor Dutu <teodor.dutu at gmail.com> ---
Using run.dlang.io, I tried to find a regression, but all supported DMD
versions (2.060 and newer) are printing the same incorrect output (Exception: i
= 0; n = 1). My experiment can be found here: https://run.dlang.io/is/uYfTzl.
This seems to be a backend issue, as both LDC and LDC-beta are working fine.

However, I came across this bug when working on this PR:
https://github.com/dlang/dmd/pull/13116. And when analysing the CI outputs, I
noticed that all 3 of DMD, LDC and GDC are failing the same test, which I've
also been able to reproduce myself:
- LDC: https://cirrus-ci.com/task/6291197929979904?logs=test_druntime#L1449
- DMD: https://cirrus-ci.com/task/5728247976558592?logs=test_druntime#L1390
- GDC: https://cirrus-ci.com/task/4883823046426624?logs=test_druntime#L1411

The failure of this test is caused by the issue I mentioned above and the code
with which I reproduced the bug is based on it.

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