Add notes describing SRT concepts

Test Plan: Read it

Reviewers: austin, erikd, simonmar

Reviewed By: simonmar

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2663

1 files changed, 12 insertions, 1 deletions

diff --git a/includes/rts/storage/InfoTables.h b/includes/rts/storage/InfoTables.h
index fb14ac5821..bb1bac0c65 100644
--- a/includes/rts/storage/InfoTables.h
+++ b/includes/rts/storage/InfoTables.h
@@ -223,10 +223,21 @@ typedef struct StgInfoTable_ {
       them doesn't affect the layout).
 
    -  If srt_bitmap (in the std info table part) is zero, then the srt
-      field may be omitted.  This only applies if the slow_apply and
+      field needn't be set.  This only applies if the slow_apply and
       bitmap fields have also been omitted.
    -------------------------------------------------------------------------- */
 
+/*
+   Note [Encoding static reference tables]
+   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+   As static reference tables appear frequently in code, we use a special
+   compact encoding for the common case of a module defining only a few CAFs: We
+   produce one table containing a list of CAFs in the module and then include a
+   bitmap in each info table describing which entries of this table the closure
+   references.
+ */
+
 typedef struct StgFunInfoExtraRev_ {
     OFFSET_FIELD(slow_apply_offset); /* apply to args on the stack */
     union {