Implement -XStaticValues

Summary:
As proposed in [1], this extension introduces a new syntactic form
`static e`, where `e :: a` can be any closed expression. The static form
produces a value of type `StaticPtr a`, which works as a reference that
programs can "dereference" to get the value of `e` back. References are
like `Ptr`s, except that they are stable across invocations of a
program.

The relevant wiki pages are [2, 3], which describe the motivation/ideas
and implementation plan respectively.

[1] Jeff Epstein, Andrew P. Black, and Simon Peyton-Jones. Towards
Haskell in the cloud. SIGPLAN Not., 46(12):118–129, September 2011. ISSN
0362-1340.
[2] https://ghc.haskell.org/trac/ghc/wiki/StaticPointers
[3] https://ghc.haskell.org/trac/ghc/wiki/StaticPointers/ImplementationPlan

Authored-by: Facundo Domínguez <facundo.dominguez@tweag.io>
Authored-by: Mathieu Boespflug <m@tweag.io>
Authored-by: Alexander Vershilov <alexander.vershilov@tweag.io>

Test Plan: `./validate`

Reviewers: hvr, simonmar, simonpj, austin

Reviewed By: simonpj, austin

Subscribers: qnikst, bgamari, mboes, carter, thomie, goldfire

Differential Revision: https://phabricator.haskell.org/D550

GHC Trac Issues: #7015

3 files changed, 37 insertions, 0 deletions

diff --git a/includes/HsFFI.h b/includes/HsFFI.h
index d51ee04b67..20be3606ed 100644
--- a/includes/HsFFI.h
+++ b/includes/HsFFI.h
@@ -161,6 +161,10 @@ extern void hs_free_stable_ptr_unsafe (HsStablePtr sp);
 extern void hs_free_stable_ptr (HsStablePtr sp);
 extern void hs_free_fun_ptr    (HsFunPtr fp);
 
+extern StgPtr hs_spt_lookup(StgWord64 key[2]);
+extern int hs_spt_keys(StgPtr keys[], int szKeys);
+extern int hs_spt_key_count (void);
+
 /* -------------------------------------------------------------------------- */
 
 #ifdef __cplusplus
diff --git a/includes/Rts.h b/includes/Rts.h
index 6bf7650f69..77eeb31f3a 100644
--- a/includes/Rts.h
+++ b/includes/Rts.h
@@ -238,6 +238,7 @@ INLINE_HEADER Time fsecondsToTime (double t)
 #include "rts/Utils.h"
 #include "rts/PrimFloat.h"
 #include "rts/Main.h"
+#include "rts/StaticPtrTable.h"
 
 /* Misc stuff without a home */
 DLL_IMPORT_RTS extern char **prog_argv; /* so we can get at these from Haskell */
diff --git a/includes/rts/StaticPtrTable.h b/includes/rts/StaticPtrTable.h
new file mode 100644
index 0000000000..8b56510223
--- /dev/null
+++ b/includes/rts/StaticPtrTable.h
@@ -0,0 +1,32 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2008-2009
+ *
+ * Initialization of the Static Pointer Table
+ *
+ * Do not #include this file directly: #include "Rts.h" instead.
+ *
+ * To understand the structure of the RTS headers, see the wiki:
+ *   http://ghc.haskell.org/trac/ghc/wiki/Commentary/SourceTree/Includes
+ *
+ * -------------------------------------------------------------------------- */
+
+#ifndef RTS_STATICPTRTABLE_H
+#define RTS_STATICPTRTABLE_H
+
+/** Inserts an entry in the Static Pointer Table.
+ *
+ * The key is a fingerprint computed from the StaticName of a static pointer
+ * and the spe_closure is a pointer to the closure defining the table entry
+ * (GHC.SptEntry).
+ *
+ * A stable pointer to the closure is made to prevent it from being garbage
+ * collected while the entry exists on the table.
+ *
+ * This function is called from the code generated by
+ * compiler/deSugar/StaticPtrTable.sptInitCode
+ *
+ * */
+void hs_spt_insert (StgWord64 key[2],void* spe_closure);
+
+#endif /* RTS_STATICPTRTABLE_H */