GitLab

I have a small example where GHC refuses to specialize a call to (+), compiling with -O2. The two files are Foo.hs (http://lpaste.net/98464) and Main.hs (http://lpaste.net/98342).

There seem to be two problems:

1. The active SPECIALIZE pragma should be applied, but isn't. This can be seen by comparing the core and runtimes of fcTest (slow) vs vtTest (fast). I need this version of the pragma in my real code as the phantom type m is reified, so I need to specialize the vector code without specifying the phantom type.
2. I can get fcTest to run fast if I use the commented-out SPECIALIZE pragma instead. However, that pragma seems very straightforward to me (all types are concrete). The docs indicate that GHC should automatically specialize in most cases, why does it not specialize to the commented-out signature automatically?

This problem is also posted here: http://stackoverflow.com/questions/21071706/specialization-with-constraints

Trac metadata

Trac field	Value
Version	7.6.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture