Re: [x32] PATCH: PR middle-end/47725: [x32] error: unable to find a register to spill in class DIREG

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

On Thu, Mar 17, 2011 at 5:30 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Feb 15, 2011 at 2:55 PM, Bernd Schmidt <bernds@codesourcery.com> wrote:
>> On 02/14/2011 08:46 PM, Eric Botcazou wrote:
>>>> I agree with Jeff that combine would be the correct place to fix this.
>>>> At least it takes class_likely_spilled_p into account, so it will
>>>> restrict only those machines where extending the lifetime of hard regs
>>>> is dangerous.
>>>
>>> OK, but I don't see how copying to a new pseudo would interfere with that.
>>
>> For one thing, the set no longer matches the REG_EQUIV note we make
>> here, and that does seem to interfere with the optimization. I've tested
>> both patches on ARM, -march=armv7-a. The combiner patch produced no code
>> changes. The function.c patch produced regressions (increased register
>> pressure). Both results are as expected.
>>
>> To put it another way: the combiner change is conservatively correct,
>> and necessary if we're going to have extends of hard registers in the
>> RTL. The function.c change is demonstrably incorrect as shown by the ARM
>> codegen regressions.
>>
>
> I checked in my patch into trunk.
>

I noticed that for x32, all pointers passed in registers are zero-extended
by caller. If we can fix

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48085

by avoiding zero-extension in callee, this issue won't happen for x32.  I will
revert the combine change for now and try to implement this approach.

Thanks.

-- 
H.J.