Unsound optimization for disjunctions?

[odersky]

#4616 failed in test-optimized, until commit 91ca4ba

My conjecture is that the optimizer rewrites E || true to true even if E is side-effecting. This caused several tests under test-optimized to fail. once I changed the code to { E; true } everything compiles fine.

[allanrenucci]

We said we would remove these optimisations since they have no measurable effects on performance and consume a lot of CI time.

cc/ @OlivierBlanvillain