[jdk17] RFR: 8268884: C2: Change to meet_speculative in phase CCP assert

[Nils Eliasson]

Hi,

The test fails on "assert(t->meet(t0) == t) failed: Not monotonic" in PhaseCCP for a CheckCastPPNode. The test is really simple. The CheckCastPP is hanging of the ParmNode for the 'this' pointer. The user of this is a call, with an infinite empty loop, that gets inlined. The loop will have a safepoint that keeps the JVM State - the CheckCastPP is kept alive by that SafePointNode.

The assert triggers because the type for the CheckCastPP has a speculative part. In the assert "assert(t->meet(t0) == t) failed: Not monotonic" - t is the type evaluated for the CheckCastPP, t0 is the previous type (from _types map), which has not been updated yet and is still Type::Top. 

t->meet(t0) will drop the speculative part and fail the comparison.

Suggested fix - change meet to meet_specualtive that will keep the speculative part.

Please review,
Best regards,
Nils Eliasson

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Commit messages:
 - Fix meet in assert

Changes: https://git.openjdk.java.net/jdk17/pull/170/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=170&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268884
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/170.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/170/head:pull/170

PR: https://git.openjdk.java.net/jdk17/pull/170