Re: DX register is not a return value for i386?

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Aug 30, 2013 at 1:54 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
> 2013/8/29 H.J. Lu <hjl.tools@gmail.com>:
>> On Thu, Aug 29, 2013 at 7:33 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>> Hi,
>>>
>>> function_value_regno_p hook implementation for i386 target
>>> (ix86_function_value_regno_p) always returns false for DX register.
>>> But DX register is used to return 128 bit values an AX:DX. Is it
>>> intentional or a bug?
>>>
>>> I'm asking because it causes problem with mode switching which fails
>>> if see 'use' insn at the end of the function whose argument is not a
>>> register holding returned value. I'm choosing what should be fixed
>>> here, a mode switching or a hook implementation.
>>>
>>
>> It is not just %dx.  %st1 and %xmm1 are used to return
>> complex value.  You need to check hard_regno_nregs for
>> how many hard registers are used.
>
> It assumes returned value is always store in consecutive registers,
> right?. In MPX when we return structure in ax:dx with bounds in
> bnd0:bnd1, it does not work.

So the problem is ax+bnd0, not ax + dx.  This is a new problem
for MPX.  For return value in DImode, bnd0 is used if return value
is a pointer.  If it is the case, you need to modify the code to handle
it.

-- 
H.J.