(set_nonzero_bits_and_sign_copies...

(set_nonzero_bits_and_sign_copies, nonzero_bits): If we have a
positive constant that is negative in the mode it is being used in,
treat it as negative.

From-SVN: r4506

diff --git a/gcc/combine.c b/gcc/combine.c
index e53d1a6b53f194526f79dc3d7e66e2820ee2ebc3..ca1567c6f0e3e1cb49aaeaf80a86497a02b7a4ad 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -692,8 +692,31 @@ set_nonzero_bits_and_sign_copies (x, set)
                  > GET_MODE_SIZE (GET_MODE (SUBREG_REG (SET_DEST (set)))))
              && SUBREG_REG (SET_DEST (set)) == x))
        {
+         rtx src = SET_SRC (set);
+
+#ifdef SHORT_IMMEDIATES_SIGN_EXTEND
+         /* If X is narrower than a word and SRC is a non-negative
+            constant that would appear negative in the mode of X,
+            sign-extend it for use in reg_nonzero_bits because some
+            machines (maybe most) will actually do the sign-extension
+            and this is the conservative approach. 
+
+            ??? For 2.5, try to tighten up the MD files in this regard
+            instead of this kludge.  */
+
+         if (GET_MODE_BITSIZE (GET_MODE (x)) < BITS_PER_WORD
+             && GET_CODE (src) == CONST_INT
+             && INTVAL (src) > 0
+             && 0 != (INTVAL (src)
+                      & ((HOST_WIDE_INT) 1
+                         << GET_MODE_BITSIZE (GET_MODE (x)))))
+           src = GEN_INT (INTVAL (src)
+                          | ((HOST_WIDE_INT) (-1)
+                             << GET_MODE_BITSIZE (GET_MODE (x))));
+#endif
+
          reg_nonzero_bits[REGNO (x)]
-           |= nonzero_bits (SET_SRC (set), nonzero_bits_mode);
+           |= nonzero_bits (src, nonzero_bits_mode);
          num = num_sign_bit_copies (SET_SRC (set), GET_MODE (x));
          if (reg_sign_bit_copies[REGNO (x)] == 0
              || reg_sign_bit_copies[REGNO (x)] > num)
@@ -6222,14 +6245,46 @@ nonzero_bits (x, mode)
        return reg_last_set_nonzero_bits[REGNO (x)];
 
       tem = get_last_value (x);
+
       if (tem)
-       return nonzero_bits (tem, mode);
+       {
+#ifdef SHORT_IMMEDIATES_SIGN_EXTEND
+         /* If X is narrower than MODE and TEM is a non-negative
+            constant that would appear negative in the mode of X,
+            sign-extend it for use in reg_nonzero_bits because some
+            machines (maybe most) will actually do the sign-extension
+            and this is the conservative approach. 
+
+            ??? For 2.5, try to tighten up the MD files in this regard
+            instead of this kludge.  */
+
+         if (GET_MODE_BITSIZE (GET_MODE (x)) < mode_width
+             && GET_CODE (tem) == CONST_INT
+             && INTVAL (tem) > 0
+             && 0 != (INTVAL (tem)
+                      & ((HOST_WIDE_INT) 1
+                         << GET_MODE_BITSIZE (GET_MODE (x)))))
+           tem = GEN_INT (INTVAL (tem)
+                          | ((HOST_WIDE_INT) (-1)
+                             << GET_MODE_BITSIZE (GET_MODE (x))));
+#endif
+         return nonzero_bits (tem, mode);
+       }
       else if (nonzero_sign_valid && reg_nonzero_bits[REGNO (x)])
        return reg_nonzero_bits[REGNO (x)] & nonzero;
       else
        return nonzero;
 
     case CONST_INT:
+#ifdef SHORT_IMMEDIATES_SIGN_EXTEND
+      /* If X is negative in MODE, sign-extend the value.  */
+      if (INTVAL (x) > 0
+         && 0 != (INTVAL (x)
+                  & ((HOST_WIDE_INT) 1 << GET_MODE_BITSIZE (GET_MODE (x)))))
+       return (INTVAL (x)
+               | ((HOST_WIDE_INT) (-1) << GET_MODE_BITSIZE (GET_MODE (x))));
+#endif
+
       return INTVAL (x);
 
 #ifdef BYTE_LOADS_ZERO_EXTEND