Eric Botcazou schrieb:
>> You are right, I was staring at the wrong place. subreg of hardreg
>> should not be there.
>
> You can take a look at PR target/48830, this is a related problem for the
> SPARC where reload generates:
>
> (set (reg:SI 708 [ D.2989+4 ])
> (subreg:SI (reg:DI 72 %f40) 4))
>
> and (subreg:SI (reg:DI 72 %f40) 4) isn't simplifiable either. H.P. wrote a
> tentative patch for the subreg machinery to forbid this. Other references
> are:
> http://gcc.gnu.org/ml/gcc-patches/2008-07/msg01688.html
> http://gcc.gnu.org/ml/gcc-patches/2008-08/msg01743.html
The problems is that find_reloads generates the wrong reload type.
It sets the reload_type of "=" operands to RELOAD_WRITE. But for
subregs as above, there are bits between inner mode and outer mode
that already contain meaningful data and that data isn't wiped out by
writing to the subreg (because outer mode is > word_mode).
Thus, a patch could look like that:
--- reload.c (Revision 173649)
+++ reload.c (Arbeitskopie)
@@ -2707,6 +2707,33 @@ find_reloads (rtx insn, int replace, int
{
case '=':
modified[i] = RELOAD_WRITE;
+
+ /* Test for SUBREGs of hard regs. */
+ {
+ rtx op = recog_data.operand[i];
+
+ if (SUBREG == GET_CODE (op)
+ && REG_P (SUBREG_REG (op))
+ && HARD_REGISTER_P (SUBREG_REG (op))
+ /* Only care for non-paradoxical subregs that have
+ some bits between innermode and outermode and
where
+ these bits don't become undefined by writing
to the
+ subreg. These bits might already contain
data. */
+ && (GET_MODE_SIZE (GET_MODE (SUBREG_REG (op)))
+ > GET_MODE_SIZE (word_mode))
+ && (GET_MODE_BITSIZE (GET_MODE (SUBREG_REG (op)))
+ > GET_MODE_BITSIZE (GET_MODE (op)))
+ /* Only care for subregs that cannot be simplified in
+ the remainder so that the inner register will
+ need reloading into some other hard register. */
+ && simplify_subreg_regno (REGNO (SUBREG_REG (op)),
+ GET_MODE (SUBREG_REG (op)),
+ SUBREG_BYTE (op),
+ GET_MODE (op)) < 0)
+ {
+ modified[i] = RELOAD_READ_WRITE;
+ }
+ }
break;
case '+':
modified[i] = RELOAD_READ_WRITE;
Is this a reasonable fix?
Johann
