Target dependence of conditional expression gimplification

[Florian Weimer <fweimer@xxxxxxxxxx>]

I have code like this:

     if (auth_info->attrs.pin.flags & SC_PKCS15_PIN_FLAG_SO_PIN) {
        preferred = 1;
    } else {
        preferred = current;
        /* PINs are even numbered, PUKs are odd */
        if (!(preferred & 1))
            preferred++;
        if (preferred >= 126)
            return SC_ERROR_TOO_MANY_OBJECTS;
    }

    if (current > preferred || preferred > CARDOS_PIN_ID_MAX)
        return SC_ERROR_TOO_MANY_OBJECTS;

On x86_64, the condition in the final if statement is gimplified as:

-  D.8003 = current > preferred;
-  D.8004 = preferred > 15;
-  D.8005 = D.8003 | D.8004;
-  if (D.8005 != 0) goto <D.8006>; else goto <D.8007>;

On rs6000 (-mtune=power7 -mcpu=power7), I get this instead:

+  if (current > preferred) goto <D.8376>; else goto <D.8378>;
+  <D.8378>:
+  if (preferred > 15) goto <D.8376>; else goto <D.8377>;

Obviously, this affects optimization-dependent warnings later in the 
compilation.

I wonder why this happens.  Shouldn't gimplification be roughly 
target-independent?

--
Florian Weimer / Red Hat Product Security Team