rts: More const correct-ness fixes

In addition to more const-correctness fixes this patch fixes an
infelicity of the previous const-correctness patch (995cf0f356) which
left `UNTAG_CLOSURE` taking a `const StgClosure` pointer parameter
but returning a non-const pointer. Here we restore the original type
signature of `UNTAG_CLOSURE` and add a new function
`UNTAG_CONST_CLOSURE` which takes and returns a const `StgClosure`
pointer and uses that wherever possible.

Test Plan: Validate on Linux, OS X and Windows

Reviewers: Phyx, hsyl20, bgamari, austin, simonmar, trofi

Reviewed By: simonmar, trofi

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2231

1 files changed, 5 insertions, 4 deletions

diff --git a/rts/sm/Compact.c b/rts/sm/Compact.c
index 4ded5bf92b..ec178e91ef 100644
--- a/rts/sm/Compact.c
+++ b/rts/sm/Compact.c
@@ -169,7 +169,8 @@ loop:
     case 1:
     {
         StgWord r = *(StgPtr)(q-1);
-        ASSERT(LOOKS_LIKE_INFO_PTR((StgWord)UNTAG_CLOSURE((StgClosure *)r)));
+        ASSERT(LOOKS_LIKE_INFO_PTR((StgWord)
+               UNTAG_CONST_CLOSURE((StgClosure *)r)));
         return r;
     }
     case 2:
@@ -539,7 +540,7 @@ update_fwd_large( bdescr *bd )
 
 // ToDo: too big to inline
 static /* STATIC_INLINE */ StgPtr
-thread_obj (StgInfoTable *info, StgPtr p)
+thread_obj (const StgInfoTable *info, StgPtr p)
 {
     switch (info->type) {
     case THUNK_0_1:
@@ -738,7 +739,7 @@ update_fwd( bdescr *blocks )
 {
     StgPtr p;
     bdescr *bd;
-    StgInfoTable *info;
+    const StgInfoTable *info;
 
     bd = blocks;
 
@@ -848,7 +849,7 @@ update_bkwd_compact( generation *gen )
     StgWord m;
 #endif
     bdescr *bd, *free_bd;
-    StgInfoTable *info;
+    const StgInfoTable *info;
     StgWord size;
     W_ free_blocks;
     StgWord iptr;