Fix glitch in gimplification of asm

[Eric Botcazou]

This fixes an old glitch in the gimplification of asm, present initially for 
clobbers and duplicated later for labels as well.  The line:

  asm ("nop" : : : "eax", "ebx");

is gimplified into:

 __asm__ __volatile__("nop" :  :  : "ebx", "eax", "eax");

in the .gimple file because the TREE_CHAIN of clobbers isn't reset to 
NULL_TREE, unlike for the outputs and the inputs.

Tested on x86_64-suse-linux, applied on the mainline as obvious.


2013-09-22  Eric Botcazou  <ebotca...@adacore.com>

        * gimplify.c (gimplify_asm_expr): Reset the TREE_CHAIN of clobbers to
        NULL_TREE before pushing them onto the vector.  Likewise for labels.


-- 
Eric Botcazou
Index: gimplify.c
===================================================================
--- gimplify.c	(revision 202812)
+++ gimplify.c	(working copy)
@@ -5419,11 +5419,21 @@ gimplify_asm_expr (tree *expr_p, gimple_
       vec_safe_push (inputs, link);
     }
 
-  for (link = ASM_CLOBBERS (expr); link; ++i, link = TREE_CHAIN (link))
-    vec_safe_push (clobbers, link);
+  link_next = NULL_TREE;
+  for (link = ASM_CLOBBERS (expr); link; ++i, link = link_next)
+    {
+      link_next = TREE_CHAIN (link);
+      TREE_CHAIN (link) = NULL_TREE;
+      vec_safe_push (clobbers, link);
+    }
 
-  for (link = ASM_LABELS (expr); link; ++i, link = TREE_CHAIN (link))
-    vec_safe_push (labels, link);
+  link_next = NULL_TREE;
+  for (link = ASM_LABELS (expr); link; ++i, link = link_next)
+    {
+      link_next = TREE_CHAIN (link);
+      TREE_CHAIN (link) = NULL_TREE;
+      vec_safe_push (labels, link);
+    }
 
   /* Do not add ASMs with errors to the gimple IL stream.  */
   if (ret != GS_ERROR)