According to spec, fmv.h checks if the input operands are correctly
 NaN-boxed. If not, the input value is treated as an n-bit canonical NaN.
 This patch fixs the issue that operands returned by soft-fp16 libgcc
 (i.e., __truncdfhf2) was not correctly NaN-boxed.

*gcc/ChangeLog:*

* config/riscv/riscv.cc (riscv_legitimize_move): Expand movfh

with Nan-boxing value.

* config/riscv/riscv.md (*movhf_softfloat_unspec): New pattern.


*gcc/testsuite/ChangeLog:*


gcc.target/riscv/_Float16-nanboxing.c: New test.