This sideband is now unused, registers are encoded directly in the IR. So we can
garbage collect all this code for quite some savings.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
I recommend viewing the new source file as the diff is quite messy.
---
The old RA commits every "how not to write an RA" sin in the book.
Chaitin spill-one loop? Check.
Potential spilling caused by alignment issues since there's no live range
splitting? Check.
Panic spilling? Check.
Generating an interference graph with linear live ranges, so you get the code
quality of linear scan with the cost of graph colouring? Check.
...
It is wholly unsuitable to any application, and specifically unsuitable for FEX.
---
The new RA exploits a key IR invariant unique to FEX: no values are live across
block boundaries. This is validated.
Because of this invariant, all RA is block local. This lets us use a dead simple
2 pass RA that generates ~optimal code in linear time.
The first pass walks the IR backwards, analyzing the IR. This is a souped up
analogue to liveness analysis.
The second pass walks the IR forward, blasting out registers. If necessary, it
will insert spill and/or shuffle code on the fly. Spilling uses the well-known
furthest-first heuristic, which has excellent results for straight line code.
That's it :-)
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
It is not an external component, and it makes paths needlessly long.
Ryan seemed amenable to this when we discussed on IRC earlier.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
LC