fold-const.c (negate_expr_p): We can optimize -((int)X>>C) where C is an integer…

fold-const.c (negate_expr_p): We can optimize -((int)X>>C) where C is an integer constant one bit less than...


	* fold-const.c (negate_expr_p) <RSHIFT_EXPR>: We can optimize
	-((int)X>>C) where C is an integer constant one bit less than the
	size of X into (unsigned)X>>C.  Similarly for unsigned->signed.
	(negate_expr) <RSHIFT_EXPR>: Implement the above transformations.

	* simplify-rtx.c (simplify_unary_operation): Also implement the
	above transformations at the RTL level.

	* gcc.c-torture/execute/20040311-1.c: New test case.

From-SVN: r79334

gcc/ChangeLog

+2004-03-11  Roger Sayle  <roger@eyesopen.com>
+
+	* fold-const.c (negate_expr_p) <RSHIFT_EXPR>: We can optimize
+	-((int)X>>C) where C is an integer constant one bit less than the
+	size of X into (unsigned)X>>C.  Similarly for unsigned->signed.
+	(negate_expr) <RSHIFT_EXPR>: Implement the above transformations.
+
+	* simplify-rtx.c (simplify_unary_operation): Also implement the
+	above transformations at the RTL level.
+
 2004-03-11  Alan Modra  <amodra@bigpond.net.au>
 
 	* real.c (encode_ibm_extended): Do round low word.

gcc/fold-const.c

@@ -920,6 +920,18 @@ negate_expr_p (tree t)
 	return negate_expr_p (TREE_VALUE (TREE_OPERAND (t, 1)));
       break;
 
+    case RSHIFT_EXPR:
+      /* Optimize -((int)x >> 31) into (unsigned)x >> 31.  */
+      if (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST)
+	{
+	  tree op1 = TREE_OPERAND (t, 1);
+	  if (TREE_INT_CST_HIGH (op1) == 0
+	      && (unsigned HOST_WIDE_INT) (TYPE_PRECISION (type) - 1)
+		 == TREE_INT_CST_LOW (op1))
+	    return true;
+	}
+      break;
+
     default:
       break;
     }
@@ -1065,6 +1077,25 @@ negate_expr (tree t)
 	}
       break;
 
+    case RSHIFT_EXPR:
+      /* Optimize -((int)x >> 31) into (unsigned)x >> 31.  */
+      if (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST)
+	{
+	  tree op1 = TREE_OPERAND (t, 1);
+	  if (TREE_INT_CST_HIGH (op1) == 0
+	      && (unsigned HOST_WIDE_INT) (TYPE_PRECISION (type) - 1)
+		 == TREE_INT_CST_LOW (op1))
+	    {
+	      tree ntype = TREE_UNSIGNED (type)
+			   ? (*lang_hooks.types.signed_type) (type)
+			   : (*lang_hooks.types.unsigned_type) (type);
+	      tree temp = fold_convert (ntype, TREE_OPERAND (t, 0));
+	      temp = fold (build2 (RSHIFT_EXPR, ntype, temp, op1));
+	      return fold_convert (type, temp);
+	    }
+	}
+      break;
+
     default:
       break;
     }

gcc/simplify-rtx.c

@@ -1013,6 +1013,22 @@ simplify_unary_operation (enum rtx_code code, enum machine_mode mode,
 					    XEXP (op, 1));
 	    }
 
+	  /* (neg (ashiftrt X C)) can be replaced by (lshiftrt X C) when
+	     C is equal to the width of MODE minus 1.  */
+	  if (GET_CODE (op) == ASHIFTRT
+	      && GET_CODE (XEXP (op, 1)) == CONST_INT
+	      && INTVAL (XEXP (op, 1)) == GET_MODE_BITSIZE (mode) - 1)
+		return simplify_gen_binary (LSHIFTRT, mode,
+					    XEXP (op, 0), XEXP (op, 1));
+
+	  /* (neg (lshiftrt X C)) can be replaced by (ashiftrt X C) when
+	     C is equal to the width of MODE minus 1.  */
+	  if (GET_CODE (op) == LSHIFTRT
+	      && GET_CODE (XEXP (op, 1)) == CONST_INT
+	      && INTVAL (XEXP (op, 1)) == GET_MODE_BITSIZE (mode) - 1)
+		return simplify_gen_binary (ASHIFTRT, mode,
+					    XEXP (op, 0), XEXP (op, 1));
+
 	  break;
 
 	case SIGN_EXTEND:

gcc/testsuite/ChangeLog

+2004-03-11  Roger Sayle  <roger@eyesopen.com>
+
+	* gcc.c-torture/execute/20040311-1.c: New test case.
+
 2004-03-11  Mark Mitchell  <mark@codesourcery.com>
 
 	PR c++/14476

gcc/testsuite/gcc.c-torture/execute/20040311-1.c

+/* Copyright (C) 2004 Free Software Foundation.
+
+   Check that constant folding and RTL simplification of -(x >> y) doesn't
+   break anything and produces the expected results.
+
+   Written by Roger Sayle, 11th March 2004.  */
+
+extern void abort (void);
+
+#define INT_BITS  (sizeof(int)*8)
+
+int test1(int x)
+{
+  return -(x >> (INT_BITS-1));
+}
+
+int test2(unsigned int x)
+{
+  return -((int)(x >> (INT_BITS-1)));
+}
+
+int test3(int x)
+{
+  int y;
+  y = INT_BITS-1;
+  return -(x >> y);
+}
+
+int test4(unsigned int x)
+{
+  int y;
+  y = INT_BITS-1;
+  return -((int)(x >> y));
+}
+
+int main()
+{
+  if (test1(0) != 0)
+    abort ();
+  if (test1(1) != 0)
+    abort ();
+  if (test1(-1) != 1)
+    abort ();
+
+  if (test2(0) != 0)
+    abort ();
+  if (test2(1) != 0)
+    abort ();
+  if (test2((unsigned int)-1) != -1)
+    abort ();
+
+  if (test3(0) != 0)
+    abort ();
+  if (test3(1) != 0)
+    abort ();
+  if (test3(-1) != 1)
+    abort ();
+
+  if (test4(0) != 0)
+    abort ();
+  if (test4(1) != 0)
+    abort ();
+  if (test4((unsigned int)-1) != -1)
+    abort ();
+
+  return 0;
+}
+