re PR c++/14755 (miscompilation in bitfielded signed integers)

	PR c++/14755
	* fold-const.c (fold) <EQ_EXPR>: Properly compute newconst in
	"bitfld++ == const" to "++bitfld == const + incr" transformations.

	* gcc.c-torture/execute/20040331-1.c: New test.
	* gcc.dg/20040331-1.c: New test.

From-SVN: r80294

gcc/ChangeLog

+2004-04-01  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/14755
+	* fold-const.c (fold) <EQ_EXPR>: Properly compute newconst in
+	"bitfld++ == const" to "++bitfld == const + incr" transformations.
+
 2004-04-01  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>
 
 	* expr.c (get_inner_reference): Use DECL_UNSIGNED, not TREE_UNSIGNED.

gcc/fold-const.c

@@ -7338,12 +7338,11 @@ fold (tree expr)
 	  /* If VAROP is a reference to a bitfield, we must mask
 	     the constant by the width of the field.  */
 	  if (TREE_CODE (TREE_OPERAND (varop, 0)) == COMPONENT_REF
-	      && DECL_BIT_FIELD(TREE_OPERAND (TREE_OPERAND (varop, 0), 1)))
+	      && DECL_BIT_FIELD (TREE_OPERAND (TREE_OPERAND (varop, 0), 1)))
 	    {
 	      tree fielddecl = TREE_OPERAND (TREE_OPERAND (varop, 0), 1);
 	      int size = TREE_INT_CST_LOW (DECL_SIZE (fielddecl));
-	      tree folded_compare;
-	      tree mask = 0;
+	      tree folded_compare, shift;
 
 	      /* First check whether the comparison would come out
 		 always the same.  If we don't do that we would
@@ -7355,25 +7354,12 @@ fold (tree expr)
 		  || integer_onep (folded_compare))
 		return omit_one_operand (type, folded_compare, varop);
 
-	      if (size < HOST_BITS_PER_WIDE_INT)
-		{
-		  unsigned HOST_WIDE_INT lo = ((unsigned HOST_WIDE_INT) 1
-					       << size) - 1;
-		  mask = build_int_2 (lo, 0);
-		}
-	      else if (size < 2 * HOST_BITS_PER_WIDE_INT)
-		{
-		  HOST_WIDE_INT hi = ((HOST_WIDE_INT) 1
-				      << (size - HOST_BITS_PER_WIDE_INT)) - 1;
-		  mask = build_int_2 (~0, hi);
-		}
-		   
-	      if (mask)
-		{
-		  mask = fold_convert (TREE_TYPE (varop), mask);
-		  newconst = fold (build2 (BIT_AND_EXPR, TREE_TYPE (varop),
-					   newconst, mask));
-		}
+	      shift = build_int_2 (TYPE_PRECISION (TREE_TYPE (varop)) - size,
+				   0);
+	      newconst = fold (build2 (LSHIFT_EXPR, TREE_TYPE (varop),
+				       newconst, shift));
+	      newconst = fold (build2 (RSHIFT_EXPR, TREE_TYPE (varop),
+				       newconst, shift));
 	    }
 
 	  return fold (build2 (code, type, varop, newconst));

gcc/testsuite/ChangeLog

+2004-04-01  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/14755
+	* gcc.c-torture/execute/20040331-1.c: New test.
+	* gcc.dg/20040331-1.c: New test.
+
 2004-04-01  Paul Brook  <paul@codesourcery.com>
 
 	* gcc.dg/arm-mmx-1.c: Add -mabi=iwmmxt to dg-options.

gcc/testsuite/gcc.c-torture/execute/20040331-1.c

+/* PR c++/14755 */
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  struct { int count: 31; } s = { 0 };
+  while (s.count--)
+    abort ();
+  exit (0);
+}

gcc/testsuite/gcc.dg/20040331-1.c

+/* { dg-do run } */
+/* { dg-options "-O2 -fwrapv" } */
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  struct { int count: 2; } s = { -2 };
+  while (s.count-- != -2)
+    abort ();
+  exit (0);
+}