guarantee RTMSpinLoopCount > 0

[Gustavo Romero]

Hi!

Jtreg test hotspot/test/compiler/rtm/locking/TestRTMSpinLoopCount.java is
failing on POWER8 due to the guarantee in

http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/88847a1b3718#l21.110

hotspot/test/compiler/rtm/locking/TestRTMSpinLoopCount.java uses
-XX:RTMSpinLoopCount=0 and so the JVM exit in one occasion through
VMError::report_and_die().

x64 seems to not have that restriction since it checks for RTMSpinLoopCount less
or equal to zero:

http://hg.openjdk.java.net/jdk9/hs/hotspot/file/3b4e4dbb855d/src/cpu/x86/vm/macroAssembler_x86.cpp#l1457

Could we do the same check on PPC64, i.e. in
http://hg.openjdk.java.net/jdk9/hs/hotspot/file/3b4e4dbb855d/src/cpu/ppc/vm/macroAssembler_ppc.cpp#l2585

check for a less or equal on decrement and guarantee(RTMSpinLoopCount >= 0)
instead?

Thanks.

Gustavo