compiler/cmm/PprC.hs: constify labels in .rodata

Consider one-line module
    module B (v) where v = "hello"
in -fvia-C mode it generates code like
    static char gibberish_str[] = "hello";

It resides in data section (precious resource on ia64!).
The patch switches genrator to emit:
    static const char gibberish_str[] = "hello";

Other types if symbols that gained 'const' qualifier are:

- info tables (from haskell and CMM)
- static reference tables (from haskell and CMM)

Cleanups along the way:

- fixed info tables defined in .cmm to reside in .rodata
- split out closure declaration into 'IC_' / 'EC_'
- added label declaration (based on label type) right before
  each label definition (based on section type) so that C
  compiler could check if declaration and definition matches
  at definition site.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: ran testsuite on unregisterised x86_64 compiler

Reviewers: simonmar, ezyang, austin, bgamari, erikd

Reviewed By: bgamari, erikd

Subscribers: rwbarton, thomie

GHC Trac Issues: #8996

Differential Revision: https://phabricator.haskell.org/D3481

3 files changed, 24 insertions, 14 deletions

diff --git a/includes/Stg.h b/includes/Stg.h
index ff5e3174c0..063959d880 100644
--- a/includes/Stg.h
+++ b/includes/Stg.h
@@ -222,13 +222,23 @@ typedef StgInt    I_;
 typedef StgWord StgWordArray[];
 typedef StgFunPtr       F_;
 
-#define EB_(X)    extern char X[]
-#define IB_(X)    static char X[]
-#define EI_(X)          extern StgWordArray (X) GNU_ATTRIBUTE(aligned (8))
-#define II_(X)          static StgWordArray (X) GNU_ATTRIBUTE(aligned (8))
+/* byte arrays (and strings): */
+#define EB_(X)    extern const char X[]
+#define IB_(X)    static const char X[]
+/* static (non-heap) closures (requires alignment for pointer tagging): */
+#define EC_(X)    extern       StgWordArray (X) GNU_ATTRIBUTE(aligned (8))
+#define IC_(X)    static       StgWordArray (X) GNU_ATTRIBUTE(aligned (8))
+/* writable data (does not require alignment): */
+#define ERW_(X)   extern       StgWordArray (X)
+#define IRW_(X)   static       StgWordArray (X)
+/* read-only data (does not require alignment): */
+#define ERO_(X)   extern const StgWordArray (X)
+#define IRO_(X)   static const StgWordArray (X)
+/* stg-native functions: */
 #define IF_(f)    static StgFunPtr GNUC3_ATTRIBUTE(used) f(void)
-#define FN_(f)    StgFunPtr f(void)
-#define EF_(f)    StgFunPtr f(void) /* External Cmm functions */
+#define FN_(f)           StgFunPtr f(void)
+#define EF_(f)           StgFunPtr f(void) /* External Cmm functions */
+/* foreign functions: */
 #define EFF_(f)   void f() /* See Note [External function prototypes] */
 
 /* Note [External function prototypes]  See Trac #8965, #11395
diff --git a/includes/rts/storage/InfoTables.h b/includes/rts/storage/InfoTables.h
index e732a30daf..3201c105e1 100644
--- a/includes/rts/storage/InfoTables.h
+++ b/includes/rts/storage/InfoTables.h
@@ -265,7 +265,7 @@ typedef struct {
 } StgFunInfoTable;
 
 // canned bitmap for each arg type, indexed by constants in FunTypes.h
-extern StgWord stg_arg_bitmaps[];
+extern const StgWord stg_arg_bitmaps[];
 
 /* -----------------------------------------------------------------------------
    Return info tables
diff --git a/includes/stg/MiscClosures.h b/includes/stg/MiscClosures.h
index 1181abcca4..725323b395 100644
--- a/includes/stg/MiscClosures.h
+++ b/includes/stg/MiscClosures.h
@@ -20,10 +20,10 @@
 #pragma once
 
 #if IN_STG_CODE
-#  define RTS_RET_INFO(i)   extern W_(i)[]
-#  define RTS_FUN_INFO(i)   extern W_(i)[]
-#  define RTS_THUNK_INFO(i) extern W_(i)[]
-#  define RTS_INFO(i)       extern W_(i)[]
+#  define RTS_RET_INFO(i)   extern const W_(i)[]
+#  define RTS_FUN_INFO(i)   extern const W_(i)[]
+#  define RTS_THUNK_INFO(i) extern const W_(i)[]
+#  define RTS_INFO(i)       extern const W_(i)[]
 #  define RTS_CLOSURE(i)    extern W_(i)[]
 #  define RTS_FUN_DECL(f)   extern DLL_IMPORT_RTS StgFunPtr f(void)
 #else
@@ -488,9 +488,9 @@ extern StgWord RTS_VAR(sched_mutex);
 
 // Apply.cmm
 // canned bitmap for each arg type
-extern StgWord stg_arg_bitmaps[];
-extern StgWord stg_ap_stack_entries[];
-extern StgWord stg_stack_save_entries[];
+extern const StgWord stg_arg_bitmaps[];
+extern const StgWord stg_ap_stack_entries[];
+extern const StgWord stg_stack_save_entries[];
 
 // Storage.c
 extern unsigned int RTS_VAR(g0);