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Date: Thu, 28 Oct 2010 12:19:34 -0700
Message-ID: <AANLkTi==BHdr3ZZNt_99tu4tbGWqz8xJQf1m4FkDMxz4@mail.gmail.com>
Subject: Re: new sign/zero extension elimination pass
From: Andrew Pinski <pinskia@gmail.com>
To: Tom de Vries <tom@codesourcery.com>
Cc: gcc-patches@gcc.gnu.org, Bernd Schmidt <bernds@codesourcery.com>
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On Thu, Oct 28, 2010 at 12:03 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Mon, Oct 18, 2010 at 8:36 AM, Tom de Vries <tom@codesourcery.com> wrote:
>> I created a new sign/zero extension elimination pass.
>>
>> The motivating example for this pass is:
>
> In the above case fwprop could do the majority of the work.  In fact
> it simplifies the (subreg (zero_extend (subreg))) into (subreg) but
> does not replace it.  I think you could extend fwprop to the correct
> thing.

Something like the attached patch.  I have not bootstrap/tested it yet
but it works for your simple example.
This allows us not to add another pass.

Thanks,
Andrew Pinski

Index: fwprop.c
===================================================================
--- fwprop.c	(revision 166031)
+++ fwprop.c	(working copy)
@@ -543,8 +543,14 @@ propagate_rtx_1 (rtx *px, rtx old_rtx, r
 	  valid_ops &= propagate_rtx_1 (&op0, old_rtx, new_rtx, flags);
           if (op0 == XEXP (x, 0))
 	    return true;
-	  tem = simplify_gen_subreg (mode, op0, GET_MODE (SUBREG_REG (x)),
-				     SUBREG_BYTE (x));
+	  tem = simplify_subreg (mode, op0, GET_MODE (SUBREG_REG (x)),
+				 SUBREG_BYTE (x));
+	  if (!tem)
+	    return false;
+	  else if (GET_CODE (tem) == SUBREG && REG_P (SUBREG_REG (tem)))
+	    valid_ops = true;
+	  else if (REG_P (tem))
+	    valid_ops = true;
 	}
       break;