A fragment of generated code (.../bin/sparcv9/java -server ...):

...
0xffffffff3854f560: smul %l7, %l4, %g0
0xffffffff3854f564: rd %y, %l2
0xffffffff3854f568: sra %l7, 0x1f, %g5
0xffffffff3854f56c: sra %l2, 0x2, %l2
0xffffffff3854f570: sra %l7, 0x1f, %g3
0xffffffff3854f574: mov %g3, %y
...

The SPARC architecture manual (version 9) says:

"The Y register is depricated; it is provided only for compatibility with
previous versions of the architecture. It should not be used in new SPARC-V9
software. It is recommended that all instructions that reference the Y register
(i.e., SMUL, SMULLcc, UMUL, UMULcc, MULScc, SDIV, SDIVcc, UDIV, UDIVcc, RDY and
WRY) be avoided."