[jdk11u-dev] RFR: 8284358: Unreachable loop is not removed from C2 IR, leading to a broken graph

[Martin Doerr]

On Tue, 11 Oct 2022 15:28:01 GMT, Goetz Lindenmaier <goetz at openjdk.org> wrote:

> I backport this for parity with 11.0.18-oracle.
> 
> I had to resolve this.
> The only reason for this I spotted is the difference
> in this comment:
> // Eagerly replace phis with top to avoid regionless phis.
> 
> I added include vectset.hpp.
> 
> The new code needs set_req_X with argument PhaseGVN.
> I added 
>   void set_req_X( uint i, Node *n, PhaseGVN *igvn );
>   to node.hpp and the implementation to phaseX.cpp.
> 
> I added an arena to the VectorSet constructor.
> 
> Flag StressIGVN is not available in 11.
> I removed it from the test and reduced the
> test cases accordingly.
> Test passes with and without the fix.

Your additions look feasible. LGTM. Thanks for backporting.

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Marked as reviewed by mdoerr (Reviewer).

PR: https://git.openjdk.org/jdk11u-dev/pull/1443