BCT optimization

[David Edelsohn]

>>>>> Joern Rennecke writes:

>> 1) Pass an empty RTX into the initialization pattern.  Have the
>> preparation statements in the pattern call gen_rtx_REG, filling in the
>> RTX.  The loop instrumentation code would then have the filled-in RTX to
>> pass as one of the parameters to the decrement_and_branch insn.

Joern> Could you elaborate what you mean with an 'empty RTX' ?

	I mean an uninitialized RTX.  The pattern would have to initialize
it.  The BCT optimization would call gen_decrement_and_branch_init() with
an RTX that was uninitialized.  The pattern would know this and initialize
that operand[] with gen_rtx_REG() or GEN_INT() whatever cookie it wanted
to hand back.

David