hoist loop-invariant code out of the loop

I'm of two minds about this... it adds register pressure and really only
tends to hoist few instructions that are fairly cheap anway.  On the
other hand, it's neat, it's easy to turn off (just set the initial
hoist value to false in Builder::push()) and it does deliver a
noticeable though slight performance improvement in the interpreter.

I think the final decision will probably come down to what we think
about maintainability?

Change-Id: Idd6346f70f03188917918406731154246a7c6fcb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/218584
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed