c-typeck.c (build_binary_op): Do not shorten unsigned right shift after sign extension.

        * c-typeck.c (build_binary_op): Do not shorten unsigned
        right shift after sign extension.

From-SVN: r44080

gcc/ChangeLog

+2001-07-17  Richard Henderson  <rth@redhat.com>
+
+	* c-typeck.c (build_binary_op): Do not shorten unsigned
+	right shift after sign extension.
+
 Tue Jul 17 16:56:05 CEST 2001  Jan Hubicka  <jh@suse.cz>
 
 	* combine.c (combine_simplify_rtx): Attempt to simplify

gcc/c-typeck.c

@@ -2469,22 +2469,12 @@ build_binary_op (code, orig_op0, orig_op1, convert_p)
 	      /* We can shorten only if the shift count is less than the
 		 number of bits in the smaller type size.  */
 	      && compare_tree_int (op1, TYPE_PRECISION (TREE_TYPE (arg0))) < 0
-	      /* If arg is sign-extended and then unsigned-shifted,
-		 we can simulate this with a signed shift in arg's type
-		 only if the extended result is at least twice as wide
-		 as the arg.  Otherwise, the shift could use up all the
-		 ones made by sign-extension and bring in zeros.
-		 We can't optimize that case at all, but in most machines
-		 it never happens because available widths are 2**N.  */
-	      && (!TREE_UNSIGNED (final_type)
-		  || unsigned_arg
-		  || (2 * TYPE_PRECISION (TREE_TYPE (arg0))
-		      <= TYPE_PRECISION (result_type))))
+	      /* We cannot drop an unsigned shift after sign-extension.  */
+	      && (!TREE_UNSIGNED (final_type) || unsigned_arg))
 	    {
 	      /* Do an unsigned shift if the operand was zero-extended.  */
 	      result_type
-		= signed_or_unsigned_type (unsigned_arg,
-					   TREE_TYPE (arg0));
+		= signed_or_unsigned_type (unsigned_arg, TREE_TYPE (arg0));
 	      /* Convert value-to-be-shifted to that type.  */
 	      if (TREE_TYPE (op0) != result_type)
 		op0 = convert (result_type, op0);

gcc/testsuite/ChangeLog

+2001-07-17  Richard Henderson  <rth@redhat.com>
+
+	* gcc.c-torture/execute/20010717-1.c: New.
+
 2001-07-17  Joseph S. Myers  <jsm28@cam.ac.uk>
 
 	* gcc.c-torture/compile/20010714-1.c, gcc.dg/format/attr-4.c: New

gcc/testsuite/gcc.c-torture/execute/20010717-1.c

+extern void abort (void);
+
+int
+main ()
+{
+  int i, j;
+  unsigned long u, r1, r2;
+
+  i = -16;
+  j = 1;
+  u = i + j;
+
+  /* no sign extension upon shift */
+  r1 = u >> 1;
+  /* sign extension upon shift, but there shouldn't be */
+  r2 = ((unsigned long) (i + j)) >> 1;
+
+  if (r1 != r2)
+    abort ();
+
+  return 0;
+}