compiler/cmm/CLabel.hs¶
Note [ticky for LNE]¶
Until 14 Feb 2013, every ticky counter was associated with a closure. Thus, ticky labels used IdLabel. It is odd that CmmBuildInfoTables.cafTransfers would consider such a ticky label reason to add the name to the CAFEnv (and thus eventually the SRT), but it was harmless because the ticky was only used if the closure was also.
Since we now have ticky counters for LNEs, it is no longer the case that every ticky counter has an actual closure. So I changed the generation of ticky counters’ CLabels to not result in their associated id ending up in the SRT.
NB IdLabel is still appropriate for ticky ids (as opposed to CmmLabel) because the LNE’s counter is still related to an .hs Id, that Id just isn’t for a proper closure.
See wiki:commentary/compiler/backends/ppr-c#prototypes
Note [Closure and info labels]¶
- For a function ‘foo, we have:
- foo_info : Points to the info table describing foo’s closure
- (and entry code for foo with tables next to code)
- foo_closure : Static (no-free-var) closure only:
- points to the statically-allocated closure
- For a data constructor (such as Just or Nothing), we have:
- Just_con_info: Info table for the data constructor itself
- the first word of a heap-allocated Just
- Just_info: Info table for the worker function, an
ordinary Haskell function of arity 1 that allocates a (Just x) box:
Just = x -> Just x
Just_closure: The closure for this worker
Nothing_closure: a statically allocated closure for Nothing Nothing_static_info: info table for Nothing_closure
All these must be exported symbol, EXCEPT Just_info. We don’t need to export this because in other modules we either have
- A reference to ‘Just’; use Just_closure
- A saturated call ‘Just x’; allocate using Just_con_info
Not exporting these Just_info labels reduces the number of symbols somewhat.
Note [Bytes label]¶
For a top-level string literal ‘foo’, we have just one symbol ‘foo_bytes’, which points to a static data block containing the content of the literal.
Note [Proc-point local block entry-points]¶
A label for a proc-point local block entry-point has no “_entry” suffix. With infoTblLbl we derive an info table label from a proc-point block ID. If we convert such an info table label into an entry label we must produce the label without an “_entry” suffix. So an info table label records the fact that it was derived from a block ID in IdLabelInfo as BlockInfoTable.
The info table label and the local block label are both local labels and are not externally visible.
