re PR middle-end/84831 (Invalid memory read in parse_output_constraint)

	PR middle-end/84831
	* stmt.c (parse_output_constraint): If the CONSTRAINT_LEN (*p, p)
	characters starting at p contain '\0' character, don't look beyond
	that.

From-SVN: r258478

gcc/ChangeLog

 2018-03-13  Jakub Jelinek  <jakub@redhat.com>
 
+	PR middle-end/84831
+	* stmt.c (parse_output_constraint): If the CONSTRAINT_LEN (*p, p)
+	characters starting at p contain '\0' character, don't look beyond
+	that.
+
 	PR target/84827
 	* config/i386/i386.md (round<mode>2): For 387 fancy math, disable
 	pattern if -ftrapping-math -fno-fp-int-builtin-inexact.

gcc/stmt.c

@@ -247,7 +247,8 @@ parse_output_constraint (const char **constraint_p, int operand_num,
     }
 
   /* Loop through the constraint string.  */
-  for (p = constraint + 1; *p; p += CONSTRAINT_LEN (*p, p))
+  for (p = constraint + 1; *p; )
+    {
       switch (*p)
 	{
 	case '+':
@@ -304,6 +305,11 @@ parse_output_constraint (const char **constraint_p, int operand_num,
 	  break;
 	}
 
+      for (size_t len = CONSTRAINT_LEN (*p, p); len; len--, p++)
+	if (*p == '\0')
+	  break;
+    }
+
   return true;
 }