On Tue, Feb 10, 2015 at 11:03:57PM -0700, Jeff Law wrote:
> On 02/09/15 19:19, Thomas Preud'homme wrote:
> >>From: Andrew Pinski [mailto:pins...@gmail.com]
> >>Sent: Tuesday, February 10, 2015 9:57 AM
> >
> >>>+#ifdef SHORT_IMMEDIATES_SIGN_EXTEND
> >>>+/* If MODE has a precision lower than PREC and SRC is a non-negative
> >>constant
> >>>+ that would appear negative in MODE, sign-extend SRC for use in
> >>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. */
> >>
> >>I don't know if this has been mentioned and even though you are just
> >>copying a comment from below but would it make sense to look fixing
> >>what the comment says we should look at after GCC 2.5 (which was over
> >>20 years ago)? Or maybe just remove the comment if it no longer
> >>applies.
> >
> >Actually this bit seems unnecessary as there is already some logic in
> >nonzero_bits1 for the CONST_INT case. So I guess the code can be
> >removed and the comment be moved there at the very least but
> >I'd prefer people from one of the affected target to test it.
I can tell you that the following doesn't trigger on an
--enable-targets=all,go powerpc64-linux bootstrap. (Ada not built due
to lack of gnat on the machine I used.) So for powerpc it looks like
the combine SHORT_IMMEDIATES_SIGN_EXTEND code can disappear. The
rtlanal.c occurrence *is* executed.
Index: gcc/combine.c
===================================================================
--- gcc/combine.c (revision 220611)
+++ gcc/combine.c (working copy)
@@ -1742,7 +1742,7 @@ set_nonzero_bits_and_sign_copies (rtx x, const_rtx
&& CONST_INT_P (src)
&& INTVAL (src) > 0
&& val_signbit_known_set_p (GET_MODE (x), INTVAL (src)))
- src = GEN_INT (INTVAL (src) | ~GET_MODE_MASK (GET_MODE (x)));
+ gcc_unreachable ();
#endif
/* Don't call nonzero_bits if it cannot change anything. */
@@ -9802,7 +9802,7 @@ reg_nonzero_bits_for_combine (const_rtx x, machine
&& CONST_INT_P (tem)
&& INTVAL (tem) > 0
&& val_signbit_known_set_p (GET_MODE (x), INTVAL (tem)))
- tem = GEN_INT (INTVAL (tem) | ~GET_MODE_MASK (GET_MODE (x)));
+ gcc_unreachable ();
#endif
return tem;
}
--
Alan Modra
Australia Development Lab, IBM
