[jdk17] RFR: 8269775: compiler/codegen/ClearArrayTest.java failed with "assert(false) failed: bad AD file"

[Sandhya Viswanathan]

On Fri, 2 Jul 2021 00:38:30 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

> The following test failed in JDK17 
> compiler/codegen/ClearArrayTest.java
> with assert(false) failed: bad AD file
> 
> The problem is that no match is found for platforms not supporting avx512vlbw for constant input.
> 
> Per analysis from Dean Long and Vladimir Kozlov:
> This is due to rep_stos rules for small clear array which use !n->in(2)->bottom_type()->is_long()->is_con(). 
> This prevents the rule from matching with a constant --> register conversion. 
> Removing !is_con() from rep_stos for small clear array fixes the issue.
> We also add appropriate "ins_cost" to all ClearArray rules, so that in the case of multiple matches, we break the tie based on ins_cost.
> 
> Best Regards,
> Sandhya

RFE for test filed: https://bugs.openjdk.java.net/browse/JDK-8269789

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PR: https://git.openjdk.java.net/jdk17/pull/199