CPR optimisation for sum types if only one constructor is used
Inspired by #3138, it might be useful for StrAnal to detect functions such as the following where only one of the data constructors for a sum type are CPRed:
loop x = case x < 10 of True -> Left x; False -> loop (x*2)We can usefully transform to:
$wloop x = case (case x < 10 of True -> Left x; False -> loop (x*2)) of Left y -> (# y #)
loop x = case loop x of (# y #) -> Left yAttached patch implements this behaviour. Most of the complication in the new code occurs because adding a DataCon field to the Demand data type means that we have to define a separate IfaceDemand type for storage in interface files.
The patch validates but I haven't done any tests on nofib. I have confirmed that the new optimisation hits on some examples, though.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.0.3 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |