re PR tree-optimization/16437 (New c-torture failures after bitfield patch)

	PR tree-optimization/16437
	* c-common.c (shorten_compare): Don't mark result of conversion to
	narrower signed type as overflowing.
	* fold-const.c (decode_field_reference): Determine whether
	signedness comes from outer type using precision rather than size.

testsuite:
	* gcc.c-torture/execute/bitfld-4.c: New test.

From-SVN: r84498

gcc/ChangeLog

+2004-07-11  Joseph S. Myers  <jsm@polyomino.org.uk>
+
+	PR tree-optimization/16437
+	* c-common.c (shorten_compare): Don't mark result of conversion to
+	narrower signed type as overflowing.
+	* fold-const.c (decode_field_reference): Determine whether
+	signedness comes from outer type using precision rather than size.
+
 2004-07-11  Phil Edwards  <phil@codesourcery.com>
 
 	* configure.ac:  Alphabetize --enable-checking list, add

gcc/c-common.c

@@ -1924,7 +1924,12 @@ shorten_compare (tree *op0_ptr, tree *op1_ptr, tree *restype_ptr,
 	*restype_ptr = c_common_signed_type (*restype_ptr);
 
       if (TREE_TYPE (primop1) != *restype_ptr)
-	primop1 = convert (*restype_ptr, primop1);
+	{
+	  tree tmp = convert (*restype_ptr, primop1);
+	  TREE_OVERFLOW (tmp) = TREE_OVERFLOW (primop1);
+	  TREE_CONSTANT_OVERFLOW (tmp) = TREE_CONSTANT_OVERFLOW (primop1);
+	  primop1 = tmp;
+	}
       if (type != *restype_ptr)
 	{
 	  minval = convert (*restype_ptr, minval);

gcc/fold-const.c

@@ -3296,7 +3296,7 @@ decode_field_reference (tree exp, HOST_WIDE_INT *pbitsize,
   /* If the number of bits in the reference is the same as the bitsize of
      the outer type, then the outer type gives the signedness. Otherwise
      (in case of a small bitfield) the signedness is unchanged.  */
-  if (outer_type && *pbitsize == tree_low_cst (TYPE_SIZE (outer_type), 1))
+  if (outer_type && *pbitsize == TYPE_PRECISION (outer_type))
     *punsignedp = TYPE_UNSIGNED (outer_type);
 
   /* Compute the mask to access the bitfield.  */

gcc/testsuite/ChangeLog

+2004-07-11  Joseph S. Myers  <jsm@polyomino.org.uk>
+
+	PR tree-optimization/16437
+	* gcc.c-torture/execute/bitfld-4.c: New test.
+
 2004-07-10  Tobias Schlueter  <tobias.schlueter@physik.uni-muenchen.de>
 	
 	* gfortran.fortran-torture/execute/common_2.f90: Add check for

gcc/testsuite/gcc.c-torture/execute/bitfld-4.c

+/* When comparisons of bit-fields to unsigned constants got shortened,
+   the shortened signed constant was wrongly marked as overflowing,
+   leading to a later integer_zerop failure and misoptimization.
+
+   Related to bug tree-optimization/16437 but shows the problem on
+   32-bit systems.  */
+/* Origin: Joseph Myers <jsm@polyomino.org.uk> */
+
+extern void abort (void);
+
+struct s { int a:12, b:20; };
+
+struct s x = { -123, -456 };
+
+int
+main (void)
+{
+  if (x.a != -123U || x.b != -456U)
+    abort ();
+  return 0;
+}