Index: i386.md
===================================================================
--- i386.md	(revision 119532)
+++ i386.md	(working copy)
@@ -18141,10 +18141,20 @@
 
 ;; Block operation instructions
 
+;; There is no need to emit cld in front of string operations, as x86 ABI
+;; mandates that the direction flag is cleared on function entry and exit.
+;; It is assumed that sane inline assembler code that sets direction flag
+;; clears it at the end of assembler block as well.
+;; Although empty, this insn pattern is kept in the machine description,
+;; so if gcc ever emits "std" instruction, then "cld" has to be emitted
+;; (probably via optimize mode switching) to clear direction flag in front
+;; of string operation and to satisfy ABI requirements on function entry
+;; and exit.
+
 (define_insn "cld"
  [(set (reg:SI DIRFLAG_REG) (const_int 0))]
  ""
- "cld"
+ ""
   [(set_attr "type" "cld")])
 
 (define_expand "movmemsi"