Michael and I were chasing an obscure bug the last two days that produced incorrect results in certain side exit conditions when the guard elimination pass was enabled. We ended up changing the side exit code to always re-execute any conditional branch that causes a side exit. This was already the case for implicit conditional checks that are the result of i.e. an array load instruction. If the null check or range check guards fail the instruction is re-executed by the interpreter. For conditional branches we previously simply side exited to the target of the conditonal branch. Instead we now always re-executed the conditional branch in question just as we do for loads and other instructions that have an implied check (i.e. null check).

Continue reading →