From d9741b61c8e446de084cc4dc609aaa8e5702118d Mon Sep 17 00:00:00 2001
From: Paul Eggert
Date: Tue, 20 Sep 2016 08:30:17 -0700
Subject: Use flexmembers on IBM XL C for AIX

This removes a workaround where Emacs did not use flexible
array members when compiled with IBM XL C.  Instead, avoid
the problem by making the aliasing issues more obvious to
this compiler.
* admin/merge-gnulib: Don’t remove m4/flexmember.m4.
* m4/flexmember.m4: Copy from gnulib.
* configure.ac (AC_C_FLEXIBLE_ARRAY_MEMBER): Remove workaround.
* src/alloc.c (allocate_string_data): Rephrase to avoid aliasing
problem that would otherwise mess up code generated for flexible
array members by IBM XL C for AIX, V12.1.
* src/conf_post.h (FLEXIBLE_ARRAY_MEMBER): Remove; now done
by gnulib code.
---
 src/alloc.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

(limited to 'src/alloc.c')

diff --git a/src/alloc.c b/src/alloc.c
index 1092a34801a..41b2f9e77d2 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2002,9 +2002,9 @@ allocate_string_data (struct Lisp_String *s,
         mallopt (M_MMAP_MAX, MMAP_MAX_AREAS);
 #endif
 
-      b->next_free = b->data;
-      b->data[0].string = NULL;
+      data = b->data;
       b->next = large_sblocks;
+      b->next_free = data;
       large_sblocks = b;
     }
   else if (current_sblock == NULL
@@ -2014,9 +2014,9 @@ allocate_string_data (struct Lisp_String *s,
     {
       /* Not enough room in the current sblock.  */
       b = lisp_malloc (SBLOCK_SIZE, MEM_TYPE_NON_LISP);
-      b->next_free = b->data;
-      b->data[0].string = NULL;
+      data = b->data;
       b->next = NULL;
+      b->next_free = data;
 
       if (current_sblock)
 	current_sblock->next = b;
@@ -2025,14 +2025,16 @@ allocate_string_data (struct Lisp_String *s,
       current_sblock = b;
     }
   else
-    b = current_sblock;
+    {
+      b = current_sblock;
+      data = b->next_free;
+    }
 
-  data = b->next_free;
+  data->string = s;
   b->next_free = (sdata *) ((char *) data + needed + GC_STRING_EXTRA);
 
   MALLOC_UNBLOCK_INPUT;
 
-  data->string = s;
   s->data = SDATA_DATA (data);
 #ifdef GC_CHECK_STRING_BYTES
   SDATA_NBYTES (data) = nbytes;
-- 
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