🚀 go-pugleaf

    Here's a question for the hardware types: is there any reason either of
    design complexity or performance to not have *all* branches (conditional
    and unconditional) save their origin somewhere (probably in a fast
    dedicated register)?  I know various cpu's (the rs6000?) have done this
    in the past, but only as an option.  If there is no negative impact to
    doing this, it would be a real win for debugging crashes where a program
    (application or kernel) branch off to nowhere and die - and the poor S/W
    type is left guessing...

Make it an option, specific to a model.

Some microarchitectures can do it easily.

Other, quite reasonable, microarchitectures can't do it at all without
slowing down (or requiring a PC to be attached to every instruction as
it flows through the pipe).

When you can do it, great! But don't slow down other implementations
for a debug feature that is not in use most of the time.

--

Andy Glew, glew@ichips.intel.com
Intel Corp., M/S JF1-19, 5200 NE Elam Young Pkwy, 
Hillsboro, Oregon 97124-6497

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