> Which is wrong when TRULY_NOOP_TRUNCATION_MODES_P is false which is
> what happens on MIPS.
>
> This patches fixes the problem by change the place where the call to
> gen_lowpart should have been gen_lowpart_or_truncate in
> simplify_comparison.
There is a similar transformation in the same function:
/* If this AND operation is really a ZERO_EXTEND from a narrower
mode, the constant fits within that mode, and this is either an
equality or unsigned comparison, try to do this comparison in
the narrower mode.
Note that in:
(ne:DI (and:DI (reg:DI 4) (const_int 0xffffffff)) (const_int 0))
-> (ne:DI (reg:SI 4) (const_int 0))
unless TRULY_NOOP_TRUNCATION allows it or the register is
known to hold a value of the required mode the
transformation is invalid. */
if ((equality_comparison_p || unsigned_comparison_p)
&& CONST_INT_P (XEXP (op0, 1))
&& (i = exact_log2 ((UINTVAL (XEXP (op0, 1))
& GET_MODE_MASK (mode))
+ 1)) >= 0
&& const_op >> i == 0
&& (tmode = mode_for_size (i, MODE_INT, 1)) != BLKmode
&& (TRULY_NOOP_TRUNCATION_MODES_P (tmode, GET_MODE (op0))
|| (REG_P (XEXP (op0, 0))
&& reg_truncated_to_mode (tmode, XEXP (op0, 0)))))
{
op0 = gen_lowpart (tmode, XEXP (op0, 0));
continue;
}
and, in this case, it is simply not done if !TRULY_NOOP_TRUNCATION_MODES_P.
I think that both transformations are equally profitable, so can we make them
agree, one way or the other?
> * gcc.c-torture/execute/20110418-1.c: New testcase.
This needs to be updated a little bit. :-)
--
Eric Botcazou
