Reason for revert:
Failures on greedy RegAlloc, Fuzzer
Original issue's description:
> Remove register index/code indirection
>
> Previous to this patch, both the lithium and TurboFan register
> allocators tracked allocated registers by "indices", rather than
> the register codes used elsewhere in the runtime. This patch
> ensures that codes are used everywhere, and in the process cleans
> up a bunch of redundant code and adds more structure to how the
> set of allocatable registers is defined.
>
> Some highlights of changes:
>
> * TurboFan's RegisterConfiguration class moved to V8's top level
> so that it can be shared with Crankshaft.
> * Various "ToAllocationIndex" and related methods removed.
> * Code that can be easily shared between Register classes on
> different platforms is now shared.
> * The list of allocatable registers on each platform is declared
> as a list rather than implicitly via the register index <->
> code mapping.
>
> Committed: https://crrev.com/80bc6f6e11f79524e3f1ad05579583adfd5f18b2
> Cr-Commit-Position: refs/heads/master@{#30913}
TBR=akos.palfi@imgtec.com,bmeurer@chromium.org,jarin@chromium.org,paul.lind@imgtec.com,titzer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Review URL: https://codereview.chromium.org/1365073002
Cr-Commit-Position: refs/heads/master@{#30914}
Previous to this patch, both the lithium and TurboFan register
allocators tracked allocated registers by "indices", rather than
the register codes used elsewhere in the runtime. This patch
ensures that codes are used everywhere, and in the process cleans
up a bunch of redundant code and adds more structure to how the
set of allocatable registers is defined.
Some highlights of changes:
* TurboFan's RegisterConfiguration class moved to V8's top level
so that it can be shared with Crankshaft.
* Various "ToAllocationIndex" and related methods removed.
* Code that can be easily shared between Register classes on
different platforms is now shared.
* The list of allocatable registers on each platform is declared
as a list rather than implicitly via the register index <->
code mapping.
Review URL: https://codereview.chromium.org/1287383003
Cr-Commit-Position: refs/heads/master@{#30913}
