RFR: 8256655: rework long counted loop handling [v3]

[Roland Westrelin]

On Fri, 20 Nov 2020 12:02:35 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> Did some quick sanity testing and `compiler/regalloc/TestC1OverlappingRegisterHint` fails with `assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int()) failed: should be one iteration`.

Thanks. That assert is broken AFAICT. It doesn't seem to account for a downward loop (which would seem to indicate that IdealLoopTree::do_one_iteration_loop() never triggered). I pushed a fix.

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PR: https://git.openjdk.java.net/jdk/pull/1316