Hi, we are experiencing test failures in test/hotspot/jtreg/compiler/vectorapi/VectorCastShape128Test.java using latest qemu:

```
zifeihan@plct-c8:~/qemu-master-riscv64/bin$ ./qemu-riscv64 -version
qemu-riscv64 version 8.1.50
Copyright (c) 2003-2023 Fabrice Bellard and the QEMU Project developers
```
By the way, using a lower version of qemu (qemu-riscv64 version 7.0.91) no such problems were encountered. we infer that version 8.1.50 of qemu adds better checks.

```
/home/zifeihan/jtreg/bin/jtreg -J-Djavatest.maxOutputSize=500000 -Djdk.lang.Process.launchMechanism=vfork -v:default -concurrency:48 -timeout:50 -javaoption:-XX:+UnlockExperimentalVMOptions -javaoption:-XX:+UseRVV -jdk:/home/zifeihan/jdk/build/linux-riscv64-server-fastdebug/jdk -compilejdk:/home/zifeihan/jdk-rvv/build/linux-x86_64-server-release/jdk /home/zifeihan/jdk/test/hotspot/jtreg/compiler/vectorapi/VectorCastShape128Test.java
```

```
----------System.out:(21/1314)----------
For random generator using seed: 262884223316435826
To re-run test with same seed value please add "-Djdk.test.lib.random.seed=262884223316435826" to command line.
#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGILL (0x4) at pc=0x00002aaab582605a, pid=1865891, tid=1868167
#
# JRE version: OpenJDK Runtime Environment (22.0) (fastdebug build 22-internal-adhoc.zifeihan.jdk)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 22-internal-adhoc.zifeihan.jdk, mixed mode, compressed oops, compressed class ptrs, g1 gc, linux-riscv64)
# Problematic frame:
# J 2181% c2 compiler.vectorapi.VectorCastShape128Test.testFloatToByte()V (111 bytes) @ 0x00002aaab582605a [0x00002aaab5825f40+0x000000000000011a]
#
# Core dump will be written. Default location: Core dumps may be processed with "/usr/share/apport/apport -p%p -s%s -c%c -d%d -P%P -u%u -g%g -- %E" (or dumping to /home/zifeihan/jdk/build/linux-riscv64-server-fastdebug/jdk/bin/JTwork/scratch/0/core.1865891)
#
# An error report file with more information is saved as:
# /home/zifeihan/jdk/build/linux-riscv64-server-fastdebug/jdk/bin/JTwork/scratch/0/hs_err_pid1865891.log
[49.618s][warning][os] Loading hsdis library failed
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#
----------System.err:(1/22)----------
```
1. SEW setting is not accurate

https://github.com/openjdk/jdk/blob/e2e8e8e210ea9a7a9d901a1da729551714015d04/src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp#L2195-L2207

The reason for the error reported for the vcvtFtoX_narrow node is because the vmfeq_vv directive is used here, but when the macro is called, the vsetvli type is set to T_SHORT, not T_FLOAT, so an exception occurs here.

For vcvtFtoL, vcvtDtoX_narrow nodes, there was also the problem of inaccurate setting of both SEW, which is also changed here.

2. Register usage constraints
For the vcvtStoX_fp_extend node, the operands of the vfwcvt_f_f_v instruction inside, the same register cannot be used here[1], so that has also been modified.

[1] https://github.com/riscv/riscv-v-spec/blob/v1.0/v-spec.adoc#sec-vec-operands