RFR: 8281429: PhiNode::Value() is too conservative for tripcount of CountedLoop [v3]

[Tobias Hartmann]

On Tue, 22 Mar 2022 13:08:33 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> The type for the iv phi of a counted loop is computed from the types
>> of the phi on loop entry and the type of the limit from the exit
>> test. Because the exit test is applied to the iv after increment, the
>> type of the iv phi is at least one less than the limit (for a positive
>> stride, one more for a negative stride).
>> 
>> Also, for a stride whose absolute value is not 1 and constant init and
>> limit values, it's possible to compute accurately the iv phi type.
>> 
>> This change caused a few failures and I had to make a few adjustments
>> to loop opts code as well.
>
> Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - review
>  - Merge branch 'master' into JDK-8281429
>  - Update src/hotspot/share/opto/cfgnode.cpp
>    
>    Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>  - Update src/hotspot/share/opto/cfgnode.cpp
>    
>    Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>  - Update src/hotspot/share/opto/loopnode.cpp
>    
>    Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>  - Update src/hotspot/share/opto/loopnode.cpp
>    
>    Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>  - fix & test

The following test triggers `assert(hi->hi_as_long() > lo->lo_as_long()) failed: no iterations?` when executed with `-XX:-TieredCompilation -Xbatch`:

``` 
public class Test {
    public static void main(String[] args) {
        for (long l = (Long.MAX_VALUE - 1); l != (Long.MIN_VALUE + 100_000); l++) {
            if (l == 0) {
                throw new RuntimeException("Test failed");
            }
        }
    }
}


Please add it as regression test.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7823