* explow.c (trunc_int_for_mode): Sign-extend value to mode.

From-SVN: r39615

gcc/ChangeLog

+2001-02-13  Alexandre Oliva  <aoliva@redhat.com>
+
+	* explow.c (trunc_int_for_mode): Sign-extend value to mode.
+
 2001-02-12  Geoffrey Keating  <geoffk@redhat.com>
 
 	* config/rs6000/sysv4.h (MASK_NO_BITFIELD_WORD): New macro.

gcc/explow.c

@@ -56,28 +56,16 @@ trunc_int_for_mode (c, mode)
   if (mode == BImode)
     return c & 1 ? STORE_FLAG_VALUE : 0;
 
-  /* We clear out all bits that don't belong in MODE, unless they and our
-     sign bit are all one.  So we get either a reasonable negative
-     value or a reasonable unsigned value.  */
-
-  if (width < HOST_BITS_PER_WIDE_INT
-      && ((c & ((HOST_WIDE_INT) (-1) << (width - 1)))
-           != ((HOST_WIDE_INT) (-1) << (width - 1))))
-    c &= ((HOST_WIDE_INT) 1 << width) - 1;
-
-  /* If this would be an entire word for the target, but is not for
-     the host, then sign-extend on the host so that the number will look
-     the same way on the host that it would on the target.
-
-     For example, when building a 64 bit alpha hosted 32 bit sparc
-     targeted compiler, then we want the 32 bit unsigned value -1 to be
-     represented as a 64 bit value -1, and not as 0x00000000ffffffff.
-     The later confuses the sparc backend.  */
-
-  if (BITS_PER_WORD < HOST_BITS_PER_WIDE_INT
-      && BITS_PER_WORD == width
-      && (c & ((HOST_WIDE_INT) 1 << (width - 1))))
-    c |= ((HOST_WIDE_INT) (-1) << width);
+  /* Sign-extend for the requested mode.  */
+
+  if (width < HOST_BITS_PER_WIDE_INT)
+    {
+      HOST_WIDE_INT sign = 1;
+      sign <<= width - 1;
+      c &= (sign << 1) - 1;
+      c ^= sign;
+      c -= sign;
+    }
 
   return c;
 }