[jdk16] RFR: 8253353: Crash in C2: guarantee(n != NULL) failed: No Node

[Nils Eliasson]

On Wed, 27 Jan 2021 21:03:43 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Nesting loops for this case reaches 400+. But the type of IdeaLoopTree::_nest field is uint8 (the maximum value allowed is 255). The test passed with the following fix proposed by @RealFYang:
> 
> - uint8_t _nest; // Nesting depth 
> + uint16_t _nest; // Nesting depth
> 
> I think increase size to `unsigned short` (16 bits) is enough for this value. We will bailout C2 compilation due to big IR graph (MaxNodeLimit = 80000) before we can construct MAX_USHORT (65535)  nested loops. And I added asserts to catch such case if it happens.
> 
> New regression test is added.
> Passed hs-tier1 - 3 testing.

Looks good.

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Marked as reviewed by neliasso (Reviewer).

PR: https://git.openjdk.java.net/jdk16/pull/135