Add -finfo-table-map which maps info tables to source positions

This new flag embeds a lookup table from the address of an info table
to information about that info table.

The main interface for consulting the map is the `lookupIPE` C function

> InfoProvEnt * lookupIPE(StgInfoTable *info)

The `InfoProvEnt` has the following structure:

> typedef struct InfoProv_{
>     char * table_name;
>     char * closure_desc;
>     char * ty_desc;
>     char * label;
>     char * module;
>     char * srcloc;
> } InfoProv;
>
> typedef struct InfoProvEnt_ {
>     StgInfoTable * info;
>     InfoProv prov;
>     struct InfoProvEnt_ *link;
> } InfoProvEnt;

The source positions are approximated in a similar way to the source
positions for DWARF debugging information. They are only approximate but
in our experience provide a good enough hint about where the problem
might be. It is therefore recommended to use this flag in conjunction
with `-g<n>` for more accurate locations.

The lookup table is also emitted into the eventlog when it is available
as it is intended to be used with the `-hi` profiling mode.

Using this flag will significantly increase the size of the resulting
object file but only by a factor of 2-3x in our experience.

1 files changed, 5 insertions, 1 deletions

diff --git a/compiler/GHC/HsToCore/Coverage.hs b/compiler/GHC/HsToCore/Coverage.hs
index df7d00071b..8180696700 100644
--- a/compiler/GHC/HsToCore/Coverage.hs
+++ b/compiler/GHC/HsToCore/Coverage.hs
@@ -1036,13 +1036,17 @@ data TickTransEnv = TTE { fileName     :: FastString
 data TickishType = ProfNotes | HpcTicks | Breakpoints | SourceNotes
                  deriving (Eq)
 
+sourceNotesEnabled :: DynFlags -> Bool
+sourceNotesEnabled dflags =
+  (debugLevel dflags > 0) || (gopt Opt_InfoTableMap dflags)
+
 coveragePasses :: DynFlags -> [TickishType]
 coveragePasses dflags =
     ifa (breakpointsEnabled dflags)          Breakpoints $
     ifa (gopt Opt_Hpc dflags)                HpcTicks $
     ifa (sccProfilingEnabled dflags &&
          profAuto dflags /= NoProfAuto)      ProfNotes $
-    ifa (debugLevel dflags > 0)              SourceNotes []
+    ifa (sourceNotesEnabled dflags)          SourceNotes []
   where ifa f x xs | f         = x:xs
                    | otherwise = xs