On July 14, 2015 6:13:13 PM GMT+02:00, Richard Earnshaw
<richard.earns...@foss.arm.com> wrote:
>On 13/07/15 16:29, Michael Matz wrote:
>> Hi,
>>
>> On Mon, 13 Jul 2015, Richard Biener wrote:
>>
>>> On Fri, Jul 10, 2015 at 5:46 PM, Jim Wilson <jim.wil...@linaro.org>
>wrote:
>>>> On Tue, Jul 7, 2015 at 2:35 PM, Richard Biener
>>>> <richard.guent...@gmail.com> wrote:
>>>>> On July 7, 2015 6:29:21 PM GMT+02:00, Jim Wilson
><jim.wil...@linaro.org> wrote:
>>>>>> signed sub-word locals. Thus to detect the need for a
>conversion, you
>>>>>> have to have the decls, and we don't have them here. There is
>also
>>>>>
>>>>> It probably is. The decks for the parameter based SSA names are
>available, for the PHI destination there might be no decl.
>>>>
>>>> I tried looking again, and found the decls. I'm able to get
>correct
>>>> code for my testcase with the attached patch to force the
>conversion.
>>>> It is rather inelegant, but I think I can cache the values I need
>to
>>>> make this simpler and cleaner. I still don't have decls from
>>>> insert_part_to_rtx_on_edge and insert_rtx_to_part_on_edge, but it
>>>> looks like those are for breaking cycles, and hence might not need
>>>> conversions.
>>>
>>> Yes, that looks like a defect. CCing Micha who wrote this code
>>
>> I think it's a backend bug that parameters and locals are extended
>> differently. The code in tree-outof-ssa was written with the
>assumption
>> that the modes of RTL objects might be different (larger) than the
>tree
>> types suggest, but that they be _consistent_, i.e. that the
>particular
>> extension depends on only the types, not on the tree-type of the
>decl.
>>
>
>We went through this a couple of weeks back. The backend documentation
>for PROMOTE_MODE says:
>
>" For most machines, the macro definition does not change
>@var{unsignedp}.
>However, some machines, have instructions that preferentially handle
>either signed or unsigned quantities of certain modes. For example, on
>the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
>sign-extend the result to 64 bits. On such machines, set
>@var{unsignedp} according to which kind of extension is more
>efficient."
>
>So clearly it anticipates that all permitted extensions should work,
>and
>in particular it makes no mention of this having to match some
>abi-mandated promotions. That makes this a MI bug not a target one.
We could also decide that it is a documentation defect. Are there any other
targets with this inconsistency?
FWIW I'd prefer to expose the promoted incoming decls after gimplification.
Independent on any inconsistency.
Richard.
>R.
>
>
>> I think the above assumption does make sense because it's also a
>> fundamental assumption in the whole gimple pipeline, types matter,
>not the
>> objects (or better, we slowly but surely work towards this). Hence
>such
>> mismatches should either not exist (changing the backend), or should
>be
>> exposed explicitely during gimplification already. The latter is a
>large
>> change, though.
>>
>> I think dealing with this situation in outof-ssa is a hack and I
>don't
>> like it. It would extend the ugliness of different modes for same
>types
>> even more, and that's something we should (gradually) move away from.
>>
>>
>> Ciao,
>> Michael.
>>
