[patch] Fix powerpc 64 alignment problem for lwa instruction

[Andrew Pinski]

> 
> > What about rejecting all low_sum instead?  The alignment is still the correct
> 									^^^^^^
> 									incorrect
> > check. Because we can have alignment of 16 and still have an offset which is
> > a multiple of 4.
> > Hmm, the other thing is that constraint m seems wrong for the lwa instruction,
> > I think it should be changed to Y like the load doubleword case.

The reason why I said this patch is incorrect is because the following:
#pragma pack(push, 2)
struct FixedRectangle {
  int left;
  int top;
  int right;
  int bottom;
};
#pragma pack(pop)

long getLeft (struct FixedRectangle *a)
{
  return ((struct FixedRectangle*)(((char*)a)+4))->top;
}


Compile at -Os -m64, we should still get a lwa but with your patch we get a
lwz and a extsw.

The following patch keeps this regression from showing up and also fixes your orginal
testcase:
Index: predicates.md
===================================================================
--- predicates.md       (revision 118565)
+++ predicates.md       (working copy)
@@ -654,7 +654,9 @@ (define_predicate "lwa_operand"
        && GET_CODE (XEXP (inner, 0)) != PRE_DEC
        && (GET_CODE (XEXP (inner, 0)) != PLUS
            || GET_CODE (XEXP (XEXP (inner, 0), 1)) != CONST_INT
-           || INTVAL (XEXP (XEXP (inner, 0), 1)) % 4 == 0));
+           || INTVAL (XEXP (XEXP (inner, 0), 1)) % 4 == 0)
+       && (GET_CODE (XEXP (inner, 0)) != LO_SUM
+           || (MEM_ALIGN (inner) % 32) == 0));
 })

 ;; Return 1 if the operand, used inside a MEM, is a SYMBOL_REF.


The main difference is just checks the alignment for the lo_sum case instead of
the general case where we don't need to check because we have an offset in those
cases.

Thanks,
Andrew Pinski