RFR: 8306933: C2: "assert(false) failed: infinite loop" failure

[Tobias Hartmann]

On Wed, 26 Apr 2023 15:36:13 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> The assert fires because an infinite loop appears in the graph after
> loop opts are over.
> 
> After loop opts, the `for(;;)` loop contains a null check and a range
> check for `array[i]`. So it's not considered an infinite loop (it has
> exits to uncommon traps). The null check and range check are redundant
> with the one right before the loop: `int v = array2[k];` IGVN can
> optimize it but it doesn't happen until after loop opts when a
> `ConvI2L` for the `array[i]` access is processed as part of post loop
> opts IGVN. The `for(;;)` loop is then emptied and only contains a
> `Loop` and a `Safepoint` nodes.
> 
> I propose removing the assert (at least for now) as I don't see a way
> to guarantee no infinite loop can appear after loop opts.

Looks good to me too (besides the missing `-XX:+UnlockDiagnosticVMOptions`).

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Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13672#pullrequestreview-1410308515