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qemu-sparc64 / sparc32plus apparent wrong results from VIS fmul8x16 instruction
Description of problem:
Experimenting with SPARC emulation, I noticed that the results of the UltraSparc fmul8x16 instruction don't appear to match the behaviour of real silicon (aka it doesn't appear to work at all -- in the test program, the result seems to be always 0). Other VIS instructions I tried seem to be OK (I have not tried all of them).
The same problem is observed both in 64-bit (qemu-sparc64) and 32-bit (qemu-sparc32plus) applications.
Steps to reproduce:
1. Compile the attached test program (which exhaustively tests all possible combinations of 16-bit and 8-bit inputs) with gcc:
```
sparc64-unknown-linux-gnu-gcc -static -Os -mcpu=ultrasparc -mvis -o test_fmul8x16 test_fmul8x16.c
```
2. Run it in qemu-sparc64:
```
qemu-sparc64 -cpu 'TI UltraSparc II' ./test_fmul8x16
```
3. Observe almost all tests fail.
Running the exact same compiled binary on a real UltraSparc II CPU gives all pass results.
Additional information:
[test_fmul8x16.c](/uploads/2bf68e53652fba2ed69ac3ebb3f4b5e9/test_fmul8x16.c)
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