re PR tree-optimization/20922 (missed always false conditional)

2005-04-18  James A. Morrison  <phython@gcc.gnu.org>

        PR tree-optimization/20922
        * fold-const.c (fold_binary): Fold X - c > X and X + c < X to false.
        Fold X + c >= X and fold X - c <= X to true.

From-SVN: r98321

gcc/ChangeLog

 2005-04-18  James A. Morrison  <phython@gcc.gnu.org>
 
+	PR tree-optimization/20922
+	* fold-const.c (fold_binary): Fold X - c > X and X + c < X to false.
+	Fold X + c >= X and fold X - c <= X to true.
+
+2005-04-18  James A. Morrison  <phython@gcc.gnu.org>
+
 	* config/ia64/unwind-ia64.c (emergency_reg_state_free): Make an
 	unsigned int.
 	(emergency_labeled_state_free): Likewise.

gcc/fold-const.c

@@ -8848,6 +8848,77 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 	    }
 	}
 
+      /* Transform comparisons of the form X +- C CMP X.  */
+      if ((code != EQ_EXPR && code != NE_EXPR)
+	  && (TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR)
+	  && operand_equal_p (TREE_OPERAND (arg0, 0), arg1, 0)
+	  && ((TREE_CODE (TREE_OPERAND (arg0, 1)) == REAL_CST
+	       && !HONOR_SNANS (TYPE_MODE (TREE_TYPE (arg0))))
+	      || (TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
+	          && !TYPE_UNSIGNED (TREE_TYPE (arg1))
+		  && !(flag_wrapv || flag_trapv))))
+	{
+	  tree arg01 = TREE_OPERAND (arg0, 1);
+	  enum tree_code code0 = TREE_CODE (arg0);
+	  int is_positive;
+
+	  if (TREE_CODE (arg01) == REAL_CST)
+	    is_positive = REAL_VALUE_NEGATIVE (TREE_REAL_CST (arg01)) ? -1 : 1;
+	  else
+	    is_positive = tree_int_cst_sgn (arg01);
+
+	  /* (X - c) > X becomes false.  */
+	  if (code == GT_EXPR
+	      && ((code0 == MINUS_EXPR && is_positive >= 0)
+		  || (code0 == PLUS_EXPR && is_positive <= 0)))
+	    return constant_boolean_node (0, type);
+
+	  /* Likewise (X + c) < X becomes false.  */
+	  if (code == LT_EXPR
+	      && ((code0 == PLUS_EXPR && is_positive >= 0)
+		  || (code0 == MINUS_EXPR && is_positive <= 0)))
+	    return constant_boolean_node (0, type);
+
+	  /* Convert (X - c) <= X to true.  */
+	  if (!HONOR_NANS (TYPE_MODE (TREE_TYPE (arg1)))
+	      && code == LE_EXPR
+	      && ((code0 == MINUS_EXPR && is_positive >= 0)
+		  || (code0 == PLUS_EXPR && is_positive <= 0)))
+	    return constant_boolean_node (1, type);
+
+	  /* Convert (X + c) >= X to true.  */
+	  if (!HONOR_NANS (TYPE_MODE (TREE_TYPE (arg1)))
+	      && code == GE_EXPR
+	      && ((code0 == PLUS_EXPR && is_positive >= 0)
+		  || (code0 == MINUS_EXPR && is_positive <= 0)))
+	    return constant_boolean_node (1, type);
+
+	  if (TREE_CODE (arg01) == INTEGER_CST)
+	    {
+	      /* Convert X + c > X and X - c < X to true for integers.  */
+	      if (code == GT_EXPR
+	          && ((code0 == PLUS_EXPR && is_positive > 0)
+		      || (code0 == MINUS_EXPR && is_positive < 0)))
+		return constant_boolean_node (1, type);
+
+	      if (code == LT_EXPR
+	          && ((code0 == MINUS_EXPR && is_positive > 0)
+		      || (code0 == PLUS_EXPR && is_positive < 0)))
+		return constant_boolean_node (1, type);
+
+	      /* Convert X + c <= X and X - c >= X to false for integers.  */
+	      if (code == LE_EXPR
+	          && ((code0 == PLUS_EXPR && is_positive > 0)
+		      || (code0 == MINUS_EXPR && is_positive < 0)))
+		return constant_boolean_node (0, type);
+
+	      if (code == GE_EXPR
+	          && ((code0 == MINUS_EXPR && is_positive > 0)
+		      || (code0 == PLUS_EXPR && is_positive < 0)))
+		return constant_boolean_node (0, type);
+	    }
+	}
+
       if (FLOAT_TYPE_P (TREE_TYPE (arg0)))
 	{
 	  tree targ0 = strip_float_extensions (arg0);

gcc/testsuite/ChangeLog

+2005-04-18  James A. Morrison  <phython@gcc.gnu.org>
+
+	PR tree-optimization/20922
+	* gcc.dg/pr20922-1.c: New test.
+	* gcc.dg/pr20922-2.c: New test.
+	* gcc.dg/pr20922-3.c: New test.
+	* gcc.dg/pr20922-4.c: New test.
+	* gcc.dg/pr20922-5.c: New test.
+	* gcc.dg/pr20922-6.c: New test.
+
 2005-04-11  Francois-Xavier Coudert  <coudert@clipper.ens.fr>
 
 	PR libfortran/20950

gcc/testsuite/gcc.dg/pr20922-1.c

+/* { dg-do compile } */
+/* { dg-options "-fno-wrapv -fdump-tree-generic" } */
+int f(int i)
+{
+  return (i - 2) > i;
+}
+
+int g(int i)
+{
+  return (i + 2) < i;
+}
+
+int h(int i)
+{
+  return (i + (-2)) > i;
+}
+
+int j(int i)
+{
+  return (i - (-2)) < i;
+}
+
+int x(double i)
+{
+  return (i - 2.0) > i;
+}
+
+int y(double i)
+{
+  return (i + 2.0) < i;
+}
+
+int z(double i)
+{
+  return (i + (-2.0)) > i;
+}
+/* { dg-final { scan-tree-dump-times " = 0" 7 "generic" } } */
+/* { dg-final { cleanup-tree-dump "generic" } } */

gcc/testsuite/gcc.dg/pr20922-2.c

+/* { dg-do compile } */
+/* { dg-options "-fwrapv -fdump-tree-generic" } */
+int f (int i)
+{
+  return (i - 2) > i;
+}
+
+int g (int i)
+{
+  return (i + 2) < i;
+}
+
+int h (double i)
+{
+  return (i + 2.0) <= i;
+}
+/* { dg-final { scan-tree-dump-times " = 0" 0 "generic" } } */
+/* { dg-final { cleanup-tree-dump "generic" } } */

gcc/testsuite/gcc.dg/pr20922-3.c

+/* { dg-do compile } */
+/* { dg-options "-ffast-math -fno-wrapv -fdump-tree-generic" } */
+int f(int i)
+{
+  return (i - 2) <= i;
+}
+
+int g(int i)
+{
+  return (i + 2) >= i;
+}
+
+int h(int i)
+{
+  return (i + (-2)) <= i;
+}
+
+int x(double i)
+{
+  return (i - 2.0) <= i;
+}
+
+int y(double i)
+{
+  return (i + 2.0) >= i;
+}
+
+int z(double i)
+{
+  return (i + (-2.0)) <= i;
+}
+/* { dg-final { scan-tree-dump-times " = 1" 6 "generic" } } */
+/* { dg-final { cleanup-tree-dump "generic" } } */

gcc/testsuite/gcc.dg/pr20922-4.c

+/* { dg-do compile } */
+/* { dg-options "-fno-wrapv -fdump-tree-generic" } */
+int f(int i)
+{
+  return i < (i - 2);
+}
+
+int g(int i)
+{
+  return i > (i + 2);
+}
+
+int h(int i)
+{
+  return i < (i + (-2));
+}
+
+int j(int i)
+{
+  return i > (i - (-2));
+}
+
+int x(double i)
+{
+  return i < (i - 2.0);
+}
+
+int y(double i)
+{
+  return i > (i + 2.0);
+}
+
+int z(double i)
+{
+  return i < (i + (-2.0));
+}
+/* { dg-final { scan-tree-dump-times " = 0" 7 "generic" } } */
+/* { dg-final { cleanup-tree-dump "generic" } } */

gcc/testsuite/gcc.dg/pr20922-5.c

+/* { dg-do compile } */
+/* { dg-options "-fsignaling-nans -fwrapv -fdump-tree-generic" } */
+int f(int i)
+{
+  return i < (i - 2);
+}
+
+int g(int i)
+{
+  return i > (i + 2);
+}
+
+int h (double i)
+{
+  return i >= i + 2.0;
+}
+
+int j (double i)
+{
+  return i > i + 2.0;
+}
+/* { dg-final { scan-tree-dump-times " = 0" 0 "generic" } } */
+/* { dg-final { cleanup-tree-dump "generic" } } */

gcc/testsuite/gcc.dg/pr20922-6.c

+/* { dg-do compile } */
+/* { dg-options "-ffast-math -fno-wrapv -fdump-tree-generic" } */
+int f(int i)
+{
+  return i >= (i - 2);
+}
+
+int g(int i)
+{
+  return i <= (i + 2);
+}
+
+int h(int i)
+{
+  return i >= (i + (-2));
+}
+
+int x(double i)
+{
+  return i >= (i - 2.0);
+}
+
+int y(double i)
+{
+  return i <= (i + 2.0);
+}
+
+int z(double i)
+{
+  return i >= (i + (-2.0));
+}
+/* { dg-final { scan-tree-dump-times " = 1" 6 "generic" } } */
+/* { dg-final { cleanup-tree-dump "generic" } } */