8346836: C2: Introduce a way to verify the correctness of ConstraintCastNodes at runtime

[merykitty]

Hi,

This patch adds a develop flag VerifyConstraintCasts, which will verify the correctness of CastIINodes and CastLLNodes at runtime and crash the VM if the dynamic value lies outside the type value range.

Please take a look, thanks a lot.

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• JDK-8346836: C2: Introduce a way to verify the correctness of ConstraintCastNodes at runtime (Enhancement - P4)

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• 00: Full (de9aea41)

[merykitty]

Running tier 1 tests with this flag and -XX:+StressGCM reveals several failures. One example is compiler.arraycopy.TestArrayCopyConjoint. In the method testByte(int, int, int), we have the final graph before matching:

228 CastII is a cast on P0 has its type being int[0, 32], it depends on 2 dominating ifs:

• 100 If, which corresponds to (P0 < 0) == false
• 200 If, which corresponds to (ConvI2L(P0) u<= 32L) == true

As a result, 228 CastII should have its control flow being the IfTrueNode projection of 200 If. However, it is incorrectly wired to the IfTrueNode projection of 223 If (P0 != 0 == true), which leads to the verification failure.