2006-02-26 Roger Sayle <roger@eyesopen.com>

[pf3gnuchains/gcc-fork.git] / gcc / fold-const.c

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 3c3852b..7eb4d91 100644 (file)
--- 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