On Mon, 27 Aug 2012, Steve Reinhardt wrote:
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Hi Nilay,
I'm a little confused by how this works. Looking at the templates in
src/arch/x86/isa/microops/regop.isa, it looks like flag_code gets
executed in the execute() method, which seems to me like it would be too
late to determine what the instruction's register dependencies are.
Can you enlighten me a bit on how this works?
The patch introduces predicates for condition code registers. These
predicates are evaluated twice -- during construction of the microop and
during its execution.
It is true that flag_code executes only during the execution of the
microop. But the isa parser gleans all the registers being used and adds
them to the constructor of the microop. Since the predicates are being
evaluated during construction as well, only those registers that are
actually required would be added to the source and destination lists of
the microop.
--
Nilay
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