> force_to_mode has
>
> /* If X is a CONST_INT, return a new one. Do this here since the
> test below will fail. */
> if (CONST_INT_P (x))
> {
> if (SCALAR_INT_MODE_P (mode))
> return gen_int_mode (INTVAL (x) & mask, mode);
> else
> {
> x = GEN_INT (INTVAL (x) & mask);
> return gen_lowpart_common (mode, x);
> }
> }
>
> /* If X is narrower than MODE and we want all the bits in X's mode, just
> get X in the proper mode. */
> if (GET_MODE_SIZE (GET_MODE (x)) < GET_MODE_SIZE (mode)
> && (GET_MODE_MASK (GET_MODE (x)) & ~mask) == 0)
> return gen_lowpart (mode, x);
>
> When it gets
>
> (zero_extend:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
> (const_int -58 [0xffffffffffffffc6])))
>
> It first sets mask to 32bit and leads to
>
> (subreg:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
> (const_int -58 [0xffffffffffffffc6])) 0)
>
> with mask == 0xffffffff. The probem is
>
> binop:
> /* For most binary operations, just propagate into the operation and
> change the mode if we have an operation of that mode. */
>
> op0 = force_to_mode (XEXP (x, 0), mode, mask, next_select);
> op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);
>
> where it calls force_to_mode with -58, 0xffffffff mask and DImode. This
> transformation is incorrect.
I think that the conclusion is questionable. If MASK is really 0xffffffff,
then you're guaranteeing to force_to_mode that you don't care about the upper
32 bits. Of course this is wrong for (zero_extend:DI ...).
So it seems to me that the origin of the problem is the transition from:
(zero_extend:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
(const_int -58 [0xffffffffffffffc6])))
to force_to_mode being invoked on:
(subreg:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
(const_int -58 [0xffffffffffffffc6])) 0)
with mask == 0xffffffff. This isn't equivalent, at least alone.
Who computes the mask and calls force_to_mode? Is it simplify_and_const_int_1?
Then it should also mask the returned value, as explained in the code:
/* Simplify VAROP knowing that we will be only looking at some of the
bits in it.
Note by passing in CONSTOP, we guarantee that the bits not set in
CONSTOP are not significant and will never be examined. We must
ensure that is the case by explicitly masking out those bits
before returning. */
varop = force_to_mode (varop, mode, constop, 0);
If this is what actually happens, why gets this masking lost somewhere?
--
Eric Botcazou
