re PR tree-optimization/21137 (Convert (a >> 2) & 1 != 0 into a & 4 != 0)

2006-02-26  Roger Sayle  <roger@eyesopen.com>
	    James A. Morrison  <phython@gcc.gnu.org>

	PR middle-end/21137
	* fold-const.c (fold_binary) <EQ_EXPR>:  Fold ((X>>C1)&C2) eq/ne 0,
	when C2 is a power of two, as either (X&(C2<<C1)) eq/ne 0 if the
	new constant C2<<C1, or as (X<0) or (X,false) depending upon the
	signedness of the shift operation.

	* gcc.dg/fold-eqandshift-1.c: New test case.


Co-Authored-By: James A. Morrison <phython@gcc.gnu.org>

From-SVN: r111453

4 files changed, 106 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 84c278d..ead872d 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2006-02-26  Roger Sayle  <roger@eyesopen.com>
+	    James A. Morrison  <phython@gcc.gnu.org>
+
+	PR middle-end/21137
+	* fold-const.c (fold_binary) <EQ_EXPR>:  Fold ((X>>C1)&C2) eq/ne 0,
+	when C2 is a power of two, as either (X&(C2<<C1)) eq/ne 0 if the
+	new constant C2<<C1, or as (X<0) or (X,false) depending upon the
+	signedness of the shift operation.
+
 2006-02-26  Dorit Nuzman  <dorit@il.ibm.com>
 
 	PR tree-optimization/26359
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 3c3852b..7eb4d91 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -9653,6 +9653,52 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 			      fold_convert (newtype, arg1));
 	}
 
+      /* Fold ((X >> C1) & C2) == 0 and ((X >> C1) & C2) != 0 where
+	 C1 is a valid shift constant, and C2 is a power of two, i.e.
+	 a single bit.  */
+      if (TREE_CODE (arg0) == BIT_AND_EXPR
+	  && TREE_CODE (TREE_OPERAND (arg0, 0)) == RSHIFT_EXPR
+	  && TREE_CODE (TREE_OPERAND (TREE_OPERAND (arg0, 0), 1))
+	     == INTEGER_CST
+	  && integer_pow2p (TREE_OPERAND (arg0, 1))
+	  && integer_zerop (arg1))
+	{
+	  tree itype = TREE_TYPE (arg0);
+	  unsigned HOST_WIDE_INT prec = TYPE_PRECISION (itype);
+	  tree arg001 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 1);
+
+	  /* Check for a valid shift count.  */
+	  if (TREE_INT_CST_HIGH (arg001) == 0
+	      && TREE_INT_CST_LOW (arg001) < prec)
+	    {
+	      tree arg01 = TREE_OPERAND (arg0, 1);
+	      tree arg000 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 0);
+	      unsigned HOST_WIDE_INT log2 = tree_log2 (arg01);
+	      /* If (C2 << C1) doesn't overflow, then ((X >> C1) & C2) != 0
+		 can be rewritten as (X & (C2 << C1)) != 0.  */
+	      if ((log2 + TREE_INT_CST_LOW (arg01)) < prec)
+		{
+		  tem = fold_build2 (LSHIFT_EXPR, itype, arg01, arg001);
+		  tem = fold_build2 (BIT_AND_EXPR, itype, arg000, tem);
+		  return fold_build2 (code, type, tem, arg1);
+		}
+	      /* Otherwise, for signed (arithmetic) shifts,
+		 ((X >> C1) & C2) != 0 is rewritten as X < 0, and
+		 ((X >> C1) & C2) == 0 is rewritten as X >= 0.  */
+	      else if (!TYPE_UNSIGNED (itype))
+		return fold_build2 (code == EQ_EXPR ? GE_EXPR : LT_EXPR, type,
+				    arg000, build_int_cst (itype, 0));
+	      /* Otherwise, of unsigned (logical) shifts,
+		 ((X >> C1) & C2) != 0 is rewritten as (X,false), and
+		 ((X >> C1) & C2) == 0 is rewritten as (X,true).  */
+	      else
+		return omit_one_operand (type,
+					 code == EQ_EXPR ? integer_one_node
+							 : integer_zero_node,
+					 arg000);
+	    }
+	}
+
       /* If this is an NE comparison of zero with an AND of one, remove the
 	 comparison since the AND will give the correct value.  */
       if (code == NE_EXPR
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3040961..deb3000 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2006-02-26  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/21137
+	* gcc.dg/fold-eqandshift-1.c: New test case.
+
 2006-02-26  Dorit Nuzman  <dorit@il.ibm.com>
 
 	PR tree-optimization/25125
diff --git a/gcc/testsuite/gcc.dg/fold-eqandshift-1.c b/gcc/testsuite/gcc.dg/fold-eqandshift-1.c
new file mode 100644
index 0000000..6de7116
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-eqandshift-1.c
@@ -0,0 +1,46 @@
+/* PR middle-end/21137  */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+extern void foo();
+
+void test1(int a)
+{
+  if ((a >> 3) & 1)
+    foo ();
+}
+
+void test2(int b)
+{
+  if ((b >> 3) & 4)
+    foo ();
+}
+
+int test3(int c)
+{
+  return (c >> 3) & 1;
+}
+
+int test4(int d)
+{
+  return (d >> 3) & 4;
+}
+
+#if 0
+void test5(int e)
+{
+  if ((e >> 31) & 64)
+    foo();
+}
+
+void test6(unsigned int f)
+{
+  if ((f >> 31) & 64)
+    foo();
+}
+#endif
+
+/* { dg-final { scan-tree-dump-times "\\(a \& 8\\) != 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "\\(b \& 32\\) != 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "c >> 3 \& 1" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "d >> 3 \& 4" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */