We were miscompiling methods which contained getfield, getstatic,
putfield, or putstatic instructions for volatile 64-bit primitives on
32-bit PowerPC due to not noticing that values in registers are clobbered
across function calls.
The solution is to create a separate Compiler::Operand instance for each
object monitor reference before and after the function call to avoid
confusing the compiler. To avoid duplicate entries in the constant pool,
we add code look for and, if found, reuse any existing entry for the same
constant.