From: Adam Nemet <anemet@caviumnetworks.com>
Date: Sat, 18 Jul 2009 21:48:19 +0000 (+0000)
Subject: combine.c (try_widen_shift_mode): Allow widening if the high-order bits are zero.
X-Git-Tag: releases/gcc-4.5.0~4514
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3e63dd3a366d314071d1568917c5a9887d113d68;p=thirdparty%2Fgcc.git

combine.c (try_widen_shift_mode): Allow widening if the high-order bits are zero.

	* combine.c (try_widen_shift_mode) <LSHIFTRT>: Allow widening if the
	high-order bits are zero.

From-SVN: r149779
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 96430050d90b..1c418d1a04b7 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2009-07-18  Adam Nemet  <anemet@caviumnetworks.com>
+
+	* combine.c (try_widen_shift_mode) <LSHIFTRT>: Allow widening if the
+	high-order bits are zero.
+
 2009-07-18  Adam Nemet  <anemet@caviumnetworks.com>
 
 	* combine.c (simplify_shift_const_1): Split code to determine
diff --git a/gcc/combine.c b/gcc/combine.c
index a0157df71406..12f0ed8223f1 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -9005,8 +9005,15 @@ try_widen_shift_mode (enum rtx_code code, rtx op,
 	  > (unsigned) (GET_MODE_BITSIZE (mode)
 			- GET_MODE_BITSIZE (orig_mode)))
 	return mode;
-      /* fall through */
+      return orig_mode;
+
     case LSHIFTRT:
+      /* Similarly here but with zero bits.  */
+      if (GET_MODE_BITSIZE (mode) <= HOST_BITS_PER_WIDE_INT
+	  && (nonzero_bits (op, mode) & ~GET_MODE_MASK (orig_mode)) == 0)
+	return mode;
+      /* fall through */
+
     case ROTATE:
       return orig_mode;