re PR middle-end/11492 (Bogus warning with -Wsign-compare)

2008-10-29  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

	PR 11492
	* c-common.c (min_precision): Move to...
	* tree.c (tree_int_cst_min_precision): ... to here. Renamed.
	* tree.h (tree_int_cst_min_precision): Declare.
	* c-common.h (min_precision): Delete declaration.
	* fold-const.c (tree_binary_nonnegative_warnv_p): Handle
	multiplication of non-negative integer constants.
	* c-decl.c (check_bitfield_type_and_width): Rename min_precision to
	tree_int_cst_min_precision.
	(finish_enum): Likewise.
cp/
	* class.c (check_bitfield_decl): Rename min_precision to
	tree_int_cst_min_precision.
	* decl.c (finish_enum): Likewise.
testsuite/
	* gcc.dg/pr11492.c: New.
	* g++.dg/warn/pr11492.C: New.

From-SVN: r141434

1 files changed, 27 insertions, 0 deletions

diff --git a/gcc/tree.c b/gcc/tree.c
index 10b50d1..184d247 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -5035,6 +5035,33 @@ tree_int_cst_sgn (const_tree t)
     return 1;
 }
 
+/* Return the minimum number of bits needed to represent VALUE in a
+   signed or unsigned type, UNSIGNEDP says which.  */
+
+unsigned int
+tree_int_cst_min_precision (tree value, bool unsignedp)
+{
+  int log;
+
+  /* If the value is negative, compute its negative minus 1.  The latter
+     adjustment is because the absolute value of the largest negative value
+     is one larger than the largest positive value.  This is equivalent to
+     a bit-wise negation, so use that operation instead.  */
+
+  if (tree_int_cst_sgn (value) < 0)
+    value = fold_build1 (BIT_NOT_EXPR, TREE_TYPE (value), value);
+
+  /* Return the number of bits needed, taking into account the fact
+     that we need one more bit for a signed than unsigned type.  */
+
+  if (integer_zerop (value))
+    log = 0;
+  else
+    log = tree_floor_log2 (value);
+
+  return log + 1 + !unsignedp;
+}
+
 /* Compare two constructor-element-type constants.  Return 1 if the lists
    are known to be equal; otherwise return 0.  */