re PR c/12818 (-fwritable strings triggers bad code generation)

	PR c/12818
	* varasm.c (const_hash_1) <STRING_CST>: Use the
	address to compute the hash value if flag_writable_strings.
	(compare_constant) <STRING_CST>: Compare the addresses
	if flag_writable_strings.
	(build_constant_desc): Do not copy the expression for a
	STRING_CST if flag_writable_strings.

From-SVN: r76958

gcc/ChangeLog

+2004-01-30  Eric Botcazou  <ebotcazou@libertysurf.fr>
+
+	PR c/12818
+	* varasm.c (const_hash_1) <STRING_CST>: Use the
+	address to compute the hash value if flag_writable_strings.
+	(compare_constant) <STRING_CST>: Compare the addresses
+	if flag_writable_strings.
+	(build_constant_desc): Do not copy the expression for a
+	STRING_CST if flag_writable_strings.
+
 2004-01-30  Jan Hubicka  <jh@suse.cz>
 
 	* alloc-pool.c: Include hashtab.h

gcc/testsuite/ChangeLog

 2004-01-30  Eric Botcazou  <ebotcazou@libertysurf.fr>
 
+	* gcc.dg/fwritable-strings-1.c: New test.
+
+2004-01-30  Eric Botcazou  <ebotcazou@libertysurf.fr>
+
 	* gcc.c-torture/compile/20040130-1.c: New test.
 
 2004-01-29  Geoffrey Keating  <geoffk@geoffk.org>

gcc/testsuite/gcc.dg/fwritable-strings-1.c

+/* PR c/12818 */
+/* Origin: <fnf@ninemoons.com> */
+
+/* { dg-do run } */
+/* { dg-options "-fwritable-strings" } */
+
+extern void abort(void);
+
+char *names[] = {"alice", "bob", "john"};
+
+int main (void)
+{
+  if (names[1][0] != 'b')
+    abort();
+
+  return 0;
+}

gcc/varasm.c

@@ -2057,7 +2057,7 @@ struct rtx_const GTY(())
 
 /* Uniquize all constants that appear in memory.
    Each constant in memory thus far output is recorded
-   in `const_hash_table'.  */
+   in `const_desc_table'.  */
 
 struct constant_descriptor_tree GTY(())
 {
@@ -2104,9 +2104,18 @@ const_hash_1 (const tree exp)
       return real_hash (TREE_REAL_CST_PTR (exp));
 
     case STRING_CST:
-      p = TREE_STRING_POINTER (exp);
-      len = TREE_STRING_LENGTH (exp);
+      if (flag_writable_strings)
+	{
+	  p = (char *) &exp;
+	  len = sizeof exp;
+	}
+      else
+	{
+	  p = TREE_STRING_POINTER (exp);
+	  len = TREE_STRING_LENGTH (exp);
+	}
       break;
+
     case COMPLEX_CST:
       return (const_hash_1 (TREE_REALPART (exp)) * 5
 	      + const_hash_1 (TREE_IMAGPART (exp)));
@@ -2221,7 +2230,7 @@ compare_constant (const tree t1, const tree t2)
 
     case STRING_CST:
       if (flag_writable_strings)
-	return 0;
+	return t1 == t2;
 
       if (TYPE_MODE (TREE_TYPE (t1)) != TYPE_MODE (TREE_TYPE (t2)))
 	return 0;
@@ -2425,7 +2434,10 @@ build_constant_desc (tree exp)
   struct constant_descriptor_tree *desc;
 
   desc = ggc_alloc (sizeof (*desc));
-  desc->value = copy_constant (exp);
+  if (flag_writable_strings && TREE_CODE (exp) == STRING_CST)
+    desc->value = exp;
+  else
+    desc->value = copy_constant (exp);
 
   /* Create a string containing the label name, in LABEL.  */
   labelno = const_labelno++;
@@ -2466,7 +2478,7 @@ build_constant_desc (tree exp)
    If DEFER is nonzero, this constant can be deferred and output only
    if referenced in the function after all optimizations.
 
-   The const_hash_table records which constants already have label strings.  */
+   `const_desc_table' records which constants already have label strings.  */
 
 rtx
 output_constant_def (tree exp, int defer)