[Mesa-dev] [PATCH] clover: fix build failure since bfd695e

[Francisco Jerez]

Ilia Mirkin <imirkin at alum.mit.edu> writes:

> On Sat, Feb 13, 2016 at 4:45 PM, Francisco Jerez <currojerez at riseup.net> wrote:
>> Ilia Mirkin <imirkin at alum.mit.edu> writes:
>>
>>> On Sat, Feb 13, 2016 at 12:01 PM, Serge Martin <edb+mesa at sigluy.net> wrote:
>>>> ---
>>>>  src/gallium/state_trackers/clover/core/kernel.cpp | 7 ++++---
>>>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/src/gallium/state_trackers/clover/core/kernel.cpp b/src/gallium/state_trackers/clover/core/kernel.cpp
>>>> index 41b3852..a4ef2b1 100644
>>>> --- a/src/gallium/state_trackers/clover/core/kernel.cpp
>>>> +++ b/src/gallium/state_trackers/clover/core/kernel.cpp
>>>> @@ -76,9 +76,10 @@ kernel::launch(command_queue &q,
>>>>                                exec.g_buffers.data(), g_handles.data());
>>>>
>>>>     // Fill information for the launch_grid() call.
>>>> -   info.block = pad_vector(q, block_size, 1).data(),
>>>> -   info.grid = pad_vector(q, reduced_grid_size, 1).data(),
>>>> -   info.pc = find(name_equals(_name), m.sysm).offset;
>>>> +   memcpy(info.block, pad_vector(q, block_size, 1).data(), sizeof(info.block));
>>>
>>> This is equivalent to
>>> int *x;
>>> {
>>>   std::vector foo = pad_vector(...);
>>>   x = foo.data();
>>> }
>>> use(x)
>>>
>>> Of course by the time you use x, the underlying vector backing it will
>>> have been freed. This was also a problem in the original code before
>>> Samuel ever touched it.
>>
>> Nope, it wasn't, both Serge's and my original code were correct.  In C++
>> the lifetime of a temporary extends until the end of the topmost
>> lexically containing expression (i.e. the end of the memcpy() call in
>> Serge's patch and the end of the launch_grid() call in my original
>> code), so it's effectively equivalent to:
>
> Huh, I didn't know that. It's either been a *really* long time since
> I've done C++, or it changed at some point. Probably the former.
>
>>
>> | {
>> |   int *x;
>> |   std::vector foo = pad_vector(...);
>> |   x = foo.data();
>> |   use(x)
>> | }
>>
>>> You could do something like...
>>>
>>> {
>>>   std::vector<uint> padded = pad_vector(...);
>>>   memcpy(info.block, padded.data(), sizeof(info.block));
>>> }
>>>
>>> and then again for the second one. I couldn't come up with a cleaner
>>> alternative... std::copy() needs the begin/end iterators, which would
>>> also require a temp var.
>>>
>>
>> That's precisely the reason clover::copy() exists (basically the same as
>> std::copy but more easily composable).  Serge, can we take v1 of your
>> patch and replace memcpy(v, u.data(), size(v)) with copy(u, v) for the
>> sake of type safety?  With that fixed:
>
> Yeah, at that point you can just do
>
> copy(pad_vector(...), info.grid)
>
> or something along those lines, depending on how the types work out.
>
Yeah, that's exactly what I had in mind.

>>
>> Reviewed-by: Francisco Jerez <currojerez at riseup.net>
>>
>>>> +   memcpy(info.grid, pad_vector(q, reduced_grid_size, 1).data(),
>>>> +                                                            sizeof(info.grid));
>>>> +   info.pc = find(name_equals(_name), m.syms).offset;
>>>>     info.input = exec.input.data();
>>>>
>>>>     q.pipe->launch_grid(q.pipe, &info);
>>>> --
>>>> 2.5.0
>>>>
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