From 2298ade7e57440cf008e0f7a2114fe37019bc2b0 Mon Sep 17 00:00:00 2001
From: Dmitry Melnik <dm@ispras.ru>
Date: Wed, 20 Oct 2010 12:26:10 +0000
Subject: [PATCH] fold-const.c (fold_binary_loc): New transformation.

2010-10-20  Dmitry Melnik  <dm@ispras.ru>

gcc/
	* fold-const.c (fold_binary_loc): New transformation.

gcc/testsuite/
	* gcc.dg/20101013-1.c: New test.

From-SVN: r165720
---
 gcc/ChangeLog                     |  4 ++++
 gcc/fold-const.c                  | 25 +++++++++++++++++++++++++
 gcc/testsuite/ChangeLog           |  4 ++++
 gcc/testsuite/gcc.dg/20101013-1.c | 11 +++++++++++
 4 files changed, 44 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/20101013-1.c

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 686b5912802..3db8d6e3446 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2010-10-20  Dmitry Melnik  <dm@ispras.ru>
+
+	* fold-const.c (fold_binary_loc): New transformation.
+
 2010-10-20  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/46085
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 808f491cbb8..decb0fba8f5 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -11599,6 +11599,31 @@ fold_binary_loc (location_t loc,
       return NULL_TREE;
 
     case TRUNC_DIV_EXPR:
+      /* Optimize (X & (-A)) / A where A is a power of 2,
+	 to X >> log2(A) */
+      if (TREE_CODE (arg0) == BIT_AND_EXPR
+	  && !TYPE_UNSIGNED (type) && TREE_CODE (arg1) == INTEGER_CST
+	  && integer_pow2p (arg1) && tree_int_cst_sgn (arg1) > 0)
+	{
+	  tree sum = fold_binary_loc (loc, PLUS_EXPR, TREE_TYPE (arg1),
+				      arg1, TREE_OPERAND (arg0, 1));
+	  if (sum && integer_zerop (sum)) {
+	    unsigned long pow2;
+
+	    if (TREE_INT_CST_LOW (arg1))
+	      pow2 = exact_log2 (TREE_INT_CST_LOW (arg1));
+	    else
+	      pow2 = exact_log2 (TREE_INT_CST_HIGH (arg1))
+		      + HOST_BITS_PER_WIDE_INT;
+
+	    return fold_build2_loc (loc, RSHIFT_EXPR, type,
+			  TREE_OPERAND (arg0, 0),
+			  build_int_cst (NULL_TREE, pow2));
+	  }
+	}
+
+      /* Fall thru */
+      
     case FLOOR_DIV_EXPR:
       /* Simplify A / (B << N) where A and B are positive and B is
 	 a power of 2, to A >> (N + log2(B)).  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index fe74a3faa10..f69e743ac40 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2010-10-20  Dmitry Melnik  <dm@ispras.ru>
+
+	* gcc.dg/20101013-1.c: New test.
+
 2010-10-20  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/46085
diff --git a/gcc/testsuite/gcc.dg/20101013-1.c b/gcc/testsuite/gcc.dg/20101013-1.c
new file mode 100644
index 00000000000..b5bd3a7ce65
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/20101013-1.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int foo(int a)
+{
+  int x = (a & (~15)) / 16;
+  return x;
+}
+
+/* { dg-final { scan-tree-dump ">>" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */