RFR: 8314580: PhaseIdealLoop::transform_long_range_checks fails with assert "was tested before"

[Vladimir Kozlov]

On Thu, 24 Aug 2023 07:57:34 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> For long counted loops, `PhaseIdealLoop::create_loop_nest()` first
> goes over the loop body to collect range checks, then transforms the
> long counted loop into a loop nest and then goes over the list of
> range checks it collected to transfrom them. For that last step,
> `PhaseIdealLoop::transform_long_range_checks()` needs to extract the
> parameters of the range check from the range check expression. It
> should still recognize the range check expression even though the loop
> was transformed in the meantime. That's what fails here. The reason is
> that the range check expression uses the long loop increment as input
> which, in the creation of the loop nest, is transformed to `outer
> phi + inner incr`. That breaks pattern matching of the range check
> expression. I propose removing the transformation:
> 
> 
> incr=>(outer_phi+inner_incr)
> 
> 
> entireley. After looking at this code again, I don't think it's
> needed. The transformation:
> 
> 
> phi=>(outer_phi+inner_phi)
> 
> 
> should be all that's needed to correctly transform the loop.

Looks good to me too. Thank you for explaining the issue in details.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15411#pullrequestreview-1603519597