RFR: 8284937: riscv: should not allocate special register for temp

[Fei Yang]

On Mon, 18 Apr 2022 08:18:27 GMT, Yanhong Zhu <yzhu at openjdk.org> wrote:

> Following testcases fail with -XX:+UseRVV after [JDK-8284863](https://bugs.openjdk.java.net/browse/JDK-8284863)：
> 
> test/hotspot/jtreg/compiler/vectorapi/VectorCastShape128Test.java
> test/hotspot/jtreg/compiler/vectorapi/VectorCastShape64Test.java
> test/hotspot/jtreg/compiler/vectorapi/VectorMaskCastTest.java
> test/hotspot/jtreg/compiler/vectorapi/VectorMaskLoadStoreTest.java
> 
> The root cause of this problem is that special registers were allocated as temporary registers in C2. Similar issue also exists in several other C2 instructs for riscv.
> 
> With this patch, testcases above are all passed.
> 
> Additional testing:
> - QEMU full with RVV enabled
> - QEMU full with RVV disabled
> - Native hotspot/jdk tier1 with RVV disabled

Looks reasonable. Thanks for fixing this.

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Marked as reviewed by fyang (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8283