RFR: 8265956: JVM crashes when matching LShiftVB Node [v3]

[Xiaohong Gong]

On Fri, 7 May 2021 09:03:14 GMT, Wang Huang <whuang at openjdk.org> wrote:

>> It is fount that the rule `match(Set dst (LShiftVB src shift))` is missing on many cpus, such like `aarch64` and `x86`. It is this reason that JVM will crash under `JDK-8265956`'s test case. In this commit, I :
>> * show the crash case `TestVectorShuffleIotaShort`
>> * solve the issue on `aarch64` and `x86` by adding the rule. 
>> * test after fixing on tire1~3
>> 
>> Thank you for your review. Any suggestion is welcome. 
>>                          Wang Huang
>
> Wang Huang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix bugs

src/hotspot/share/opto/vectorIntrinsics.cpp line 372:

> 370:   } else if (step_val->get_con() > 1) {
> 371:     Node* cnt = gvn().makecon(TypeInt::make(log2i_exact(step_val->get_con())));
> 372:     Node* shift_cnt = gvn().transform(new LShiftCntVNode(cnt, vt));

Use "vector_shift_count"?  It will mask the shift count before generating the `LShiftCntVNode`.

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PR: https://git.openjdk.java.net/jdk/pull/3747