The requirement to keep micro-ops dense while optimizing is harmful.

[markshannon]

The tier 2 executor creation requires optimization passes to compact the micro-ops, which is onerous and error-prone.

We should make it part of the job of creating the executor to compact the micro-ops.
We will want to modify the tier 2 instruction format, so we will need to do this anyway at some point.

Linked PRs

• GH-111646: Simplify optimizer, by compacting uops when making executor. #111647

[mdboom]

Can you elaborate on what you mean by "compact the microops"? Is this removing unnecessary microops and (perhaps) realloc'ing a smaller buffer and copying there?

[markshannon]

Packing them together instead of leaving gaps.
So

Some uop
NOP
NOP
Another uop
JUMP to exit
# Junk here 
exit:
# More uops here

must be compacted to:

Some uop
Another uop
JUMP to exit
exit:
# More uops here

during optimization, rather than doing it once when creating the executor.

[mdboom]

Thanks, that makes sense.