[release/5.0] Fix regression with tail.callvirt transformation to helper call #45880
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…ed to compute the target function pointer in morph.cpp
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Backport of #45527 to release/5.0
Customer Impact
The original issue was reported by @KevinRansom - F# 5.0.100 was broken for Linux Arm32 (dotnet/fsharp#10454). He also constructed a short F# repro exposing the bug in #45250.
Later, I discovered that the issue can be reproduced on all platforms if fast tail calls are either disabled or disallowed (e.g. when
locallocis used in the caller method).The issue impacts F# applications with the following code pattern
and results in side effects being computed twice when such code is transformed to tail call with helpers.
Testing
Constructed a regression test in IL that exposes the failing code pattern (see Runtime_45250.il). Confirmed that the test would fail on all platforms due to incorrect JIT transformation (bad silent codegen). Verified that the change fixes the issue. Ran Pri1 tests in various jit-stress modes. Manually collected the code differences introduced by the change and analyzed some of the differences.
Risk
Low.
Regression
Yes from 3.1, introduced when runtime switched to using tail call with portable helpers.