Assertion failure when executing RISC-V vfncvt.rtz.x.f.w instruction

Host environment

• Operating system: RHEL 8.6
• OS/kernel version: 4.18.0-372.19.1.el8_6.x86_64
• Architecture: x86
• QEMU flavor: qemu-riscv64
• QEMU version: 7.2.50

Emulated/Virtualized environment

• Architecture: RISC-V

Description of problem

When emulating the vfncvt.rtz.x.f.w instruction, QEMU crashes with an assertion failure at target/riscv/translate.c:211, complaining that decode_save_opc: Assertion `ctx->insn_start != NULL' failed.

It appears this problem first emerged with a9814e3e

Steps to reproduce

The following C program triggers the assertion failure when built a sufficiently recent version of the Clang cross compiler (in my case 15.0.6):

/* test.c */
#include <riscv_vector.h>

#define LEN 4

int main(int argc, char *argv[]) {
  double in[LEN];
  int out[LEN];

  vfloat64m1_t vf = vle64_v_f64m1(in, LEN);
  vint32mf2_t vi = vfncvt_rtz_x_f_w_i32mf2(vf, LEN);
  vse32_v_i32mf2(out, vi, LEN);

  return 0;
}

The above test.c can be compiled and run as follows:

clang -O3 -march=rv64gcv -static test.c
qemu-riscv64 -cpu "rv64,zba=true,zbb=true,zbc=true,zbs=true,v=true,vlen=512,elen=64,vext_spec=v1.0" a.out
qemu-riscv64: ../target/riscv/translate.c:211: decode_save_opc: Assertion `ctx->insn_start != NULL' failed.
Segmentation fault (core dumped)

Additional information