need to have a 'preserved registers' option for stoke search about stoke HOT 3 CLOSED

This should be easy to implement, there's already more or less
functionality for it.

Look in src/search/transforms.cc. There's a method called
set_operand_pool() which determines the set of operands that get proposed
by a transformation. Right now, the only flag that affects this is the
--callee-save flag. I'd suggest replacing this flag with
--preserved-registers { ... }, since it'll let you do what you want and
generalizes the behavior of that flag nicely.

On Fri, Oct 3, 2014 at 8:38 AM, Berkeley Churchill <[email protected]

wrote:

When optimizing a basic block, often the basic block will need to preserve
the value of a register without ever touching it. Right now, there are two
ways to have stoke do this:

(1) Make these 'preserved registers' both part of def-ins and live-outs.
If we do so, STOKE will propose moves that use data from these preserved
registers, even if they shouldn't be used. This makes the search space
larger, with most of this added size being deadweight.
(2) Make these 'preserved registers' neighther live-in nor live-out.
However, then these registers could be used and we lose soundness.

So, I propose having an option to specify registers which cannot ever be
read from or written to. This, like the dataflow analysis, can be used to
eliminate bad proposals before trying them. When I get a chance I'll create
a branch and implement this.

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#39.

from stoke.

It looks like you haven't started this yet, so I'll take it over. Should be a quick enhancement.

from stoke.

Done with this; merge with develop for changes.

I've generalized the behavior of --callee_save which would override the default behavior of not proposing callee-save registers. The new implementation expects an argument --preserve_args which takes a set of registers that stoke will not attempt to modify.

To preserve backwards compatibility, the default value of preserve_args is the set of callee save registers, and specifying the --callee_save flag overrides the value of preserve_args to the empty set.

from stoke.