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Re: [PATCH, PowerPC] altivec_expand_vec_perm_const reverses pack pattern arguments in little endian mode



On Mon, 2013-07-22 at 19:49 -0400, David Edelsohn wrote:
> On Mon, Jul 22, 2013 at 7:05 PM, Bill Schmidt
> <wschmidt@linux.vnet.ibm.com> wrote:
> > This patch is another fix for vector handling in little endian mode.
> > The first two operands for a pack pattern are two vector registers that
> > form a contiguous array of inputs.  In LE mode the order of the operands
> > must be reversed so that the array remains contiguous in the reverse
> > order.
> >
> > This fixes a failure in the testsuite when run little-endian
> > (gcc.dg/vect/no-scevccp-outer-18.c).  Bootstrapped and tested big-endian
> > on powerpc64-unknown-linux-gnu with no new regressions.  Ok for trunk?
> >
> > Patch by Anton Blanchard.
> >
> > Thanks,
> > Bill
> >
> >
> > 2013-07-22  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
> >             Anton Blanchard <anton@au1.ibm.com>
> >
> >         * config/rs6000/rs6000.c (altivec_expand_vec_perm_const): Reverse
> >         two operands for little-endian.
> 
> Wouldn't it be better to handle this where the code is performing a
> swap a few lines above?

OK, currently testing the following.  OK if it passes?

Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	(revision 201149)
+++ gcc/config/rs6000/rs6000.c	(working copy)
@@ -28518,6 +28518,11 @@ altivec_expand_vec_perm_const (rtx operands[4])
 	  enum machine_mode omode = insn_data[icode].operand[0].mode;
 	  enum machine_mode imode = insn_data[icode].operand[1].mode;
 
+	  /* For little-endian, the two input operands must be swapped
+	     (or swapped back) to ensure proper right-to-left numbering
+	     from 0 to 2N-1.  */
+          if (!BYTES_BIG_ENDIAN)
+            swapped = !swapped;
 	  if (swapped)
 	    x = op0, op0 = op1, op1 = x;
 	  if (imode != V16QImode)

Thanks,
Bill

> 
> Thanks, David
> 


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