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Re: [PATCH] Optimize nested SIGN_EXTENDs/ZERO_EXTENDs (PR target/45336)


On Fri, Aug 20, 2010 at 11:46:48AM +0200, Paolo Bonzini wrote:
> On 08/19/2010 06:33 PM, Jakub Jelinek wrote:
> >+      /* (sign_extend:M (sign_extend:N<X>)) is (sign_extend:M<X>).  */
> >+      if (GET_CODE (op) == SIGN_EXTEND)
> >+	return simplify_gen_unary (SIGN_EXTEND, mode, XEXP (op, 0),
> >+				   GET_MODE (XEXP (op, 0)));
> 
> Maybe
> 
> /* (sign_extend:M (sign_extend:N<X>)) is (sign_extend:M<X>).
>    (sign_extend:M (zero_extend:N<X>)) is (zero_extend:M<X>).  */
> if (GET_CODE (op) == SIGN_EXTEND || GET_CODE (op) == ZERO_EXTEND)
>   {
>     gcc_assert (GET_MODE (op) != mode);
>     return simplify_gen_unary (GET_CODE (op), mode, XEXP (op, 0),
>                                GET_MODE (XEXP (op, 0)));
>   }
> 
> ?

Good idea.

On Thu, Aug 19, 2010 at 07:58:24PM +0200, Bernd Schmidt wrote:
> > ZERO_EXTEND is expanded into AND instead of LSHIFTRT/ASHIFT by combine,
> > and
> > two nested ANDs should be easily optimized.  If you really want, I can
> > handle the ZERO_EXTEND (AND <X> mask) case as a follow-up.
> 
> Oh, in expand_compound_operation?  I was thinking about finding such
> shifts in a pair of insns (happens on Thumb).  Also, what about callers
> other than combine?

Ok.  The following patch thus adds optimization of sign_extend of zero_extend,
sign_extend of lshiftrt/ashift and zero_extend of lshiftrt/ashift.

Bootstrapped/regtested on x86_64-linux and i686-linux (yes,rtl checking)
with additional patchlet to gather statistics and in both
bootstraps/regtests together this optimization happened (the fact that
simplify-rtx.c simplified it doesn't still mean the result was usable in
whatever pass asked for it)	times:
(sign_extend (sign_extend))	 2059
(sign_extend (zero_extend))	87019
(sign_extend (ashiftrt))	 1485
(zero_extend (zero_extend))	15648
lshiftrt wasn't seen, but it is very well possible it shows up on other
targets.  Ok for trunk?

2010-08-20  Jakub Jelinek  <jakub@redhat.com>
	    Paolo Bonzini  <bonzini@gnu.org>

	* simplify-rtx.c (simplify_unary_operation_1): Optimize
	(sign_extend (zero_extend ()) and
	({sign,zero}_extend (lshiftrt (ashift X (const_int I)) (const_int I))).

--- gcc/simplify-rtx.c.jj	2010-08-20 12:33:30.000000000 +0200
+++ gcc/simplify-rtx.c	2010-08-20 13:11:15.000000000 +0200
@@ -1010,15 +1010,22 @@ simplify_unary_operation_1 (enum rtx_cod
 	  && GET_MODE_SIZE (mode) <= GET_MODE_SIZE (GET_MODE (XEXP (op, 0))))
 	return rtl_hooks.gen_lowpart_no_emit (mode, op);
 
-      /* (sign_extend:M (sign_extend:N <X>)) is (sign_extend:M <X>).  */
-      if (GET_CODE (op) == SIGN_EXTEND)
-	return simplify_gen_unary (SIGN_EXTEND, mode, XEXP (op, 0),
-				   GET_MODE (XEXP (op, 0)));
+      /* (sign_extend:M (sign_extend:N <X>)) is (sign_extend:M <X>).
+	 (sign_extend:M (zero_extend:N <X>)) is (zero_extend:M <X>).  */
+      if (GET_CODE (op) == SIGN_EXTEND || GET_CODE (op) == ZERO_EXTEND)
+	{
+	  gcc_assert (GET_MODE_BITSIZE (mode)
+		      > GET_MODE_BITSIZE (GET_MODE (op)));
+	  return simplify_gen_unary (GET_CODE (op), mode, XEXP (op, 0),
+				     GET_MODE (XEXP (op, 0)));
+	}
 
       /* (sign_extend:M (ashiftrt:N (ashift <X> (const_int I)) (const_int I)))
 	 is (sign_extend:M (subreg:O <X>)) if there is mode with
-	 GET_MODE_BITSIZE (N) - I bits.  */
-      if (GET_CODE (op) == ASHIFTRT
+	 GET_MODE_BITSIZE (N) - I bits.
+	 (sign_extend:M (lshiftrt:N (ashift <X> (const_int I)) (const_int I)))
+	 is similarly (zero_extend:M (subreg:O <X>)).  */
+      if ((GET_CODE (op) == ASHIFTRT || GET_CODE (op) == LSHIFTRT)
 	  && GET_CODE (XEXP (op, 0)) == ASHIFT
 	  && CONST_INT_P (XEXP (op, 1))
 	  && XEXP (XEXP (op, 0), 1) == XEXP (op, 1)
@@ -1027,11 +1034,15 @@ simplify_unary_operation_1 (enum rtx_cod
 	  enum machine_mode tmode
 	    = mode_for_size (GET_MODE_BITSIZE (GET_MODE (op))
 			     - INTVAL (XEXP (op, 1)), MODE_INT, 1);
+	  gcc_assert (GET_MODE_BITSIZE (mode)
+		      > GET_MODE_BITSIZE (GET_MODE (op)));
 	  if (tmode != BLKmode)
 	    {
 	      rtx inner =
 		rtl_hooks.gen_lowpart_no_emit (tmode, XEXP (XEXP (op, 0), 0));
-	      return simplify_gen_unary (SIGN_EXTEND, mode, inner, tmode);
+	      return simplify_gen_unary (GET_CODE (op) == ASHIFTRT
+					 ? SIGN_EXTEND : ZERO_EXTEND,
+					 mode, inner, tmode);
 	    }
 	}
 
@@ -1066,6 +1077,26 @@ simplify_unary_operation_1 (enum rtx_cod
 	return simplify_gen_unary (ZERO_EXTEND, mode, XEXP (op, 0),
 				   GET_MODE (XEXP (op, 0)));
 
+      /* (zero_extend:M (lshiftrt:N (ashift <X> (const_int I)) (const_int I)))
+	 is (zero_extend:M (subreg:O <X>)) if there is mode with
+	 GET_MODE_BITSIZE (N) - I bits.  */
+      if (GET_CODE (op) == LSHIFTRT
+	  && GET_CODE (XEXP (op, 0)) == ASHIFT
+	  && CONST_INT_P (XEXP (op, 1))
+	  && XEXP (XEXP (op, 0), 1) == XEXP (op, 1)
+	  && GET_MODE_BITSIZE (GET_MODE (op)) > INTVAL (XEXP (op, 1)))
+	{
+	  enum machine_mode tmode
+	    = mode_for_size (GET_MODE_BITSIZE (GET_MODE (op))
+			     - INTVAL (XEXP (op, 1)), MODE_INT, 1);
+	  if (tmode != BLKmode)
+	    {
+	      rtx inner =
+		rtl_hooks.gen_lowpart_no_emit (tmode, XEXP (XEXP (op, 0), 0));
+	      return simplify_gen_unary (ZERO_EXTEND, mode, inner, tmode);
+	    }
+	}
+
 #if defined(POINTERS_EXTEND_UNSIGNED) && !defined(HAVE_ptr_extend)
       /* As we do not know which address space the pointer is refering to,
 	 we can do this only if the target does not support different pointer


	Jakub


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