See the attached Test.java

Manifestation:
- assert in debug
- miscompilation / wrong result in product.

Code of the assert / vectorization of Float.float16ToFloat was added in JDK-8294588

Discovered by Template Framework (work in progress): JDK-8344942

----------------------------------- Debug:

java -Xbatch -XX:+TraceSuperWord -XX:CompileCommand=compileonly,Test::test Test.java

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/oracle-work/jdk-fork6/open/src/hotspot/share/opto/vectornode.cpp:1500), pid=2137199, tid=2137213
# Error: assert(bt == T_SHORT) failed
#
# JRE version: Java(TM) SE Runtime Environment (25.0) (fastdebug build 25-internal-LTS-2025-02-24-0956096.emanuel...)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 25-internal-LTS-2025-02-24-0956096.emanuel..., mixed mode, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x192c4a0] VectorCastNode::opcode(int, BasicType, bool)+0x170
#
# 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 /oracle-work/jdk-fork0/build/linux-x64-debug/jdk/bin/core.2137199)
#
# An error report file with more information is saved as:
# /oracle-work/jdk-fork0/build/linux-x64-debug/jdk/bin/hs_err_pid2137199.log
#
# Compiler replay data is saved as:
# /oracle-work/jdk-fork0/build/linux-x64-debug/jdk/bin/replay_pid2137199.log
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#
Aborted (core dumped)


---------------------------------------- Product:

java -Xbatch -XX:CompileCommand=compileonly,Test::test -XX:CompileCommand=printassembly,Test::test Test.java

We see that we vectorize, but with the wrong instructions:

  0x00007c0ae8bafc36: vmovdqu 0x10(%r10,%r8,1),%xmm0
  0x00007c0ae8bafc3d: vmovdqu 0x80(%r10,%r8,1),%xmm7
  0x00007c0ae8bafc47: vmovdqu 0x20(%r10,%r8,1),%xmm1
  0x00007c0ae8bafc4e: vmovdqu 0x30(%r10,%r8,1),%xmm2
  0x00007c0ae8bafc55: vmovdqu 0x40(%r10,%r8,1),%xmm3
  0x00007c0ae8bafc5c: vmovdqu 0x50(%r10,%r8,1),%xmm4
  0x00007c0ae8bafc63: vmovdqu 0x60(%r10,%r8,1),%xmm5
  0x00007c0ae8bafc6a: vmovdqu 0x70(%r10,%r8,1),%xmm6
  0x00007c0ae8bafc71: vcvtph2ps %ymm0,%zmm0
  0x00007c0ae8bafc77: vmovdqu32 %zmm0,0x10(%r9,%r8,4)
  0x00007c0ae8bafc82: vcvtph2ps %ymm6,%zmm0
  0x00007c0ae8bafc88: vcvtph2ps %ymm5,%zmm5
  0x00007c0ae8bafc8e: vcvtph2ps %ymm4,%zmm4
  0x00007c0ae8bafc94: vcvtph2ps %ymm3,%zmm3
  0x00007c0ae8bafc9a: vcvtph2ps %ymm2,%zmm2
  0x00007c0ae8bafca0: vcvtph2ps %ymm1,%zmm1
  0x00007c0ae8bafca6: vmovdqu32 %zmm1,0x50(%r9,%r8,4)
  0x00007c0ae8bafcb1: vmovdqu32 %zmm2,0x90(%r9,%r8,4)
  0x00007c0ae8bafcbc: vmovdqu32 %zmm3,0xd0(%r9,%r8,4)
  0x00007c0ae8bafcc7: vmovdqu32 %zmm4,0x110(%r9,%r8,4) ; {no_reloc}
  0x00007c0ae8bafcd2: vmovdqu32 %zmm5,0x150(%r9,%r8,4)
  0x00007c0ae8bafcdd: vmovdqu32 %zmm0,0x190(%r9,%r8,4)
  0x00007c0ae8bafce8: vcvtph2ps %ymm7,%zmm0
  0x00007c0ae8bafcee: vmovdqu32 %zmm0,0x1d0(%r9,%r8,4)


Exception in thread "main" java.lang.RuntimeException: wrong value: -0.02746582 4.7683716E-7
at Test.main(Test.java:31)