Merge from origin/emacs-27

44c0e074f7 * doc/emacs/buffers.texi (Icomplete): Mention icomplete-mi...
68b6dad1d8 Be more aggressive in marking objects during GC
36f508f589 ; * src/xdisp.c (find_last_unchanged_at_beg_row): Fix a typo.
cc340da1fe Fix bug #41618 "(byte-compile 'foo) errors when foo is a m...
41232e6797 Avoid crashes due to bidi cache being reset during redisplay
f72bb4ce36 * lisp/tab-bar.el (switch-to-buffer-other-tab): Normalize ...
d3e0023aaa ; * etc/TODO: Fix formatting.  (Bug#41497)
a8ad94cd2f Fix mingw.org's MinGW GCC 9 warning about 'execve'

# Conflicts:
#	lisp/tab-bar.el
#	nt/inc/ms-w32.h
#	src/alloc.c

1 files changed, 10 insertions, 33 deletions

diff --git a/src/alloc.c b/src/alloc.c
index e241b9933a4..124b50d0d3f 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -4687,35 +4687,6 @@ mark_maybe_objects (Lisp_Object const *array, ptrdiff_t nelts)
     mark_maybe_object (*array);
 }
 
-/* A lower bound on the alignment of Lisp objects that need marking.
-   Although 1 is safe, higher values speed up mark_maybe_pointer.
-   If USE_LSB_TAG, this value is typically GCALIGNMENT; otherwise,
-   it's determined by the natural alignment of Lisp structs.
-   All vectorlike objects have alignment at least that of union
-   vectorlike_header and it's unlikely they all have alignment greater,
-   so use the union as a safe and likely-accurate standin for
-   vectorlike objects.  */
-
-enum { GC_OBJECT_ALIGNMENT_MINIMUM
-         = max (GCALIGNMENT,
-		min (alignof (union vectorlike_header),
-		     min (min (alignof (struct Lisp_Cons),
-			       alignof (struct Lisp_Float)),
-			  min (alignof (struct Lisp_String),
-			       alignof (struct Lisp_Symbol))))) };
-
-/* Return true if P might point to Lisp data that can be garbage
-   collected, and false otherwise (i.e., false if it is easy to see
-   that P cannot point to Lisp data that can be garbage collected).
-   Symbols are implemented via offsets not pointers, but the offsets
-   are also multiples of GC_OBJECT_ALIGNMENT_MINIMUM.  */
-
-static bool
-maybe_lisp_pointer (void *p)
-{
-  return (uintptr_t) p % GC_OBJECT_ALIGNMENT_MINIMUM == 0;
-}
-
 /* If P points to Lisp data, mark that as live if it isn't already
    marked.  */
 
@@ -4728,9 +4699,6 @@ mark_maybe_pointer (void *p)
   VALGRIND_MAKE_MEM_DEFINED (&p, sizeof (p));
 #endif
 
-  if (!maybe_lisp_pointer (p))
-    return;
-
   if (pdumper_object_p (p))
     {
       int type = pdumper_find_object_type (p);
@@ -4830,7 +4798,16 @@ mark_memory (void const *start, void const *end)
 
   for (pp = start; (void const *) pp < end; pp += GC_POINTER_ALIGNMENT)
     {
-      mark_maybe_pointer (*(void *const *) pp);
+      char *p = *(char *const *) pp;
+      mark_maybe_pointer (p);
+
+      /* Unmask any struct Lisp_Symbol pointer that make_lisp_symbol
+	 previously disguised by adding the address of 'lispsym'.
+	 On a host with 32-bit pointers and 64-bit Lisp_Objects,
+	 a Lisp_Object might be split into registers saved into
+	 non-adjacent words and P might be the low-order word's value.  */
+      p += (intptr_t) lispsym;
+      mark_maybe_pointer (p);
 
       verify (alignof (Lisp_Object) % GC_POINTER_ALIGNMENT == 0);
       if (alignof (Lisp_Object) == GC_POINTER_ALIGNMENT