RFR: 8323582: C2 SuperWord AlignVector: misaligned vector memory access with unaligned native memory

[Emanuel Peter]

On Tue, 18 Feb 2025 09:53:14 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> @rwestrel I only see `if (!C->too_many_traps(reason)) {` in `PhaseIdealLoop::add_parse_predicate`. And as the comment I put here that only checks the `reason` per `method`, and not per `bci`. Do you see anything else?
>
> Seems like it's a bug that `PhaseIdealLoop::add_parse_predicate` doesn't check the `bci` too. Could you fix it?

@rwestrel So we would check both, right? But is that what we want for all predicates?

`C->too_many_traps(reason)` checks against `PerMethodTrapLimit`:

if (trap_count(reason) >= Deoptimization::per_method_trap_limit(reason)) {


But the `bci` check works with `PerBytecodeTrapLimit`, and it actually has a comment like this:

if (md->has_trap_at(bci, m, reason) != 0) {
  // Assume PerBytecodeTrapLimit==0, for a more conservative heuristic.
  // Also, if there are multiple reasons, or if there is no per-BCI record,
  // assume the worst.

So the `bci` check fails if there has been even a single trapping recorded.

So it seems that such a change would affect the behavior in ways I cannot yet predict.

What do you think?

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PR Review Comment: https://git.openjdk.org/jdk/pull/22016#discussion_r1959431345