target-i386: Avoid repeated calls to the bnd_jmp helper

Two flags were tested the wrong way.
Tested-by: NHervé Poussineau <hpoussin@reactos.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <1456845145-18891-1-git-send-email-pbonzini@redhat.com>
Signed-off-by: NRichard Henderson <rth@twiddle.net>
[rth: Fixed enable test as well.]

target-i386/translate.c

@@ -2409,12 +2409,12 @@ static void gen_reset_hflag(DisasContext *s, uint32_t mask)
 /* Clear BND registers during legacy branches.  */
 static void gen_bnd_jmp(DisasContext *s)
 {
-    /* Do nothing if BND prefix present, MPX is disabled, or if the
-       BNDREGs are known to be in INIT state already.  The helper
-       itself will check BNDPRESERVE at runtime.  */
+    /* Clear the registers only if BND prefix is missing, MPX is enabled,
+       and if the BNDREGs are known to be in use (non-zero) already.
+       The helper itself will check BNDPRESERVE at runtime.  */
     if ((s->prefix & PREFIX_REPNZ) == 0
-        && (s->flags & HF_MPX_EN_MASK) == 0
-        && (s->flags & HF_MPX_IU_MASK) == 0) {
+        && (s->flags & HF_MPX_EN_MASK) != 0
+        && (s->flags & HF_MPX_IU_MASK) != 0) {
         gen_helper_bnd_jmp(cpu_env);
     }
 }