Verify that Qnil is zero before relying on that in redisplay.

 src/dispnew.c (adjust_glyph_matrix, realloc_glyph_pool): Verify that
 Qnil is represented as zero, before using that to initialize parts
 of the glyph structure.
 src/xdisp.c (init_iterator): Verify that Qnil is represented as
 zero, before using that to initialize parts of the iterator
 structure.

3 files changed, 25 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 04b952cae60..f6a5f3837a3 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,13 @@
+2015-01-19  Eli Zaretskii  <eliz@gnu.org>
+
+        * dispnew.c (adjust_glyph_matrix, realloc_glyph_pool): Verify that
+        Qnil is represented as zero, before using that to initialize parts
+        of the glyph structure.
+
+        * xdisp.c (init_iterator): Verify that Qnil is represented as
+        zero, before using that to initialize parts of the iterator
+        structure.
+
 2015-01-19  Paul Eggert  <eggert@cs.ucla.edu>
 
         Prefer memset to repeatedly assigning Qnil
diff --git a/src/dispnew.c b/src/dispnew.c
index a643d58e492..4aaf6db3a86 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -413,6 +413,12 @@ adjust_glyph_matrix (struct window *w, struct glyph_matrix *matrix, int x, int y
       new_rows = dim.height - matrix->rows_allocated;
       matrix->rows = xpalloc (matrix->rows, &matrix->rows_allocated,
                               new_rows, INT_MAX, sizeof *matrix->rows);
+      /* As a side effect, this sets the object of each glyph in the
+         row to nil, so verify we will indeed get that.  Redisplay
+         relies on the object of special glyphs (truncation and
+         continuation glyps and also blanks used to extend each line
+         on a TTY) to be nil.  */
+      verify (NIL_IS_ZERO);
       memset (matrix->rows + old_alloc, 0,
               (matrix->rows_allocated - old_alloc) * sizeof *matrix->rows);
     }
@@ -1339,6 +1345,12 @@ realloc_glyph_pool (struct glyph_pool *pool, struct dim matrix_dim)
       ptrdiff_t old_nglyphs = pool->nglyphs;
       pool->glyphs = xpalloc (pool->glyphs, &pool->nglyphs,
                               needed - old_nglyphs, -1, sizeof *pool->glyphs);
+      /* As a side effect, this sets the object of each glyph to nil,
+         so verify we will indeed get that.  Redisplay relies on the
+         object of special glyphs (truncation and continuation glyps
+         and also blanks used to extend each line on a TTY) to be
+         nil.  */
+      verify (NIL_IS_ZERO);
       memset (pool->glyphs + old_nglyphs, 0,
               (pool->nglyphs - old_nglyphs) * sizeof *pool->glyphs);
     }
diff --git a/src/xdisp.c b/src/xdisp.c
index f006f8e0b94..2442367d3b5 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -2747,6 +2747,9 @@ init_iterator (struct it *it, struct window *w,
     }
 
   /* Clear IT.  */
+  /* As a side effect, this sets it->object to nil, so verify we will
+     indeed get that.  */
+  verify (NIL_IS_ZERO);
   memset (it, 0, sizeof *it);
   it->current.overlay_string_index = -1;
   it->current.dpvec_index = -1;