Runtime regression to RTS change

The commit to fix #12799 (closed), namely changeset:1732d7ac, seems to have introduced a runtime regression. The hidden and integer nofib benchmarks regress by 5.5% resp. 2.5%:

https://perf.haskell.org/ghc/#revision/1732d7ac43ca578deca39ea5a63cbf34f3cd9dd5

I re-measured this commit and its parent once, and the numbers aid not change much.

The hidden regression seems to be offset almost completely by the later changeset:6f7ed1e5 while the integer regression got “fixed” by the later changeset:1732d7ac.

The perf builder is still new, so this might be bogus. But we should still check.

Also, maybe random changes to the RTS cause random changes to the code layout which surface here. Or there is a real cause.

Simon Marlow suggested to open a high priority ticket for this.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	simonmar
Operating system
Architecture