[Mesa-dev] [PATCH 1/2] nir: Use alloca instead of variable length arrays.
Jason Ekstrand
jason at jlekstrand.net
Mon Mar 2 12:03:33 PST 2015
On Mon, Mar 2, 2015 at 8:02 AM, Jose Fonseca <jfonseca at vmware.com> wrote:
> On 27/02/15 16:15, Brian Paul wrote:
>
>> On 02/27/2015 09:10 AM, Ian Romanick wrote:
>>
>>> On 02/26/2015 10:07 AM, Brian Paul wrote:
>>>
>>>> On 02/26/2015 09:51 AM, Jose Fonseca wrote:
>>>>
>>>>> This is to enable the code to build with -Werror=vla in the short term,
>>>>> and enable the code to build with MSVC2013 soon after.
>>>>> ---
>>>>> include/c99_alloca.h | 45
>>>>> ++++++++++++++++++++++++++++++++++++
>>>>> src/glsl/nir/nir_from_ssa.c | 19 +++++++--------
>>>>> src/glsl/nir/nir_live_variables.c | 5 ++--
>>>>> src/glsl/nir/nir_lower_vars_to_ssa.c | 13 +++++++----
>>>>> 4 files changed, 66 insertions(+), 16 deletions(-)
>>>>> create mode 100644 include/c99_alloca.h
>>>>>
>>>>> diff --git a/include/c99_alloca.h b/include/c99_alloca.h
>>>>> new file mode 100644
>>>>> index 0000000..6d96d06
>>>>> --- /dev/null
>>>>> +++ b/include/c99_alloca.h
>>>>> @@ -0,0 +1,45 @@
>>>>> +/**********************************************************
>>>>> ****************
>>>>>
>>>>>
>>>>> + *
>>>>> + * Copyright 2015 VMware, Inc.
>>>>> + * All Rights Reserved.
>>>>> + *
>>>>> + * Permission is hereby granted, free of charge, to any person
>>>>> obtaining a
>>>>> + * copy of this software and associated documentation files (the
>>>>> + * "Software"), to deal in the Software without restriction, including
>>>>> + * without limitation the rights to use, copy, modify, merge, publish,
>>>>> + * distribute, sub license, and/or sell copies of the Software, and to
>>>>> + * permit persons to whom the Software is furnished to do so,
>>>>> subject to
>>>>> + * the following conditions:
>>>>> + *
>>>>> + * The above copyright notice and this permission notice (including
>>>>> the
>>>>> + * next paragraph) shall be included in all copies or substantial
>>>>> portions
>>>>> + * of the Software.
>>>>> + *
>>>>> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
>>>>> EXPRESS
>>>>> + * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
>>>>> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
>>>>> NON-INFRINGEMENT.
>>>>> + * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
>>>>> + * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
>>>>> CONTRACT,
>>>>> + * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
>>>>> + * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
>>>>> + *
>>>>> +
>>>>> ************************************************************
>>>>> **************/
>>>>>
>>>>>
>>>>> +
>>>>> +#ifndef _C99_ALLOCA_H_
>>>>> +#define _C99_ALLOCA_H_
>>>>> +
>>>>> +
>>>>> +#if defined(_MSC_VER)
>>>>> +
>>>>> +# include <malloc.h>
>>>>> +
>>>>> +# define alloca _alloca
>>>>> +
>>>>> +#else /* !defined(_MSC_VER) */
>>>>> +
>>>>> +# include <alloca.h>
>>>>> +
>>>>> +#endif /* !defined(_MSC_VER) */
>>>>> +
>>>>> +
>>>>> +#endif
>>>>> diff --git a/src/glsl/nir/nir_from_ssa.c b/src/glsl/nir/nir_from_ssa.c
>>>>> index c695c95..66339f3 100644
>>>>> --- a/src/glsl/nir/nir_from_ssa.c
>>>>> +++ b/src/glsl/nir/nir_from_ssa.c
>>>>> @@ -26,6 +26,7 @@
>>>>> */
>>>>>
>>>>> #include "nir.h"
>>>>> +#include "c99_alloca.h"
>>>>>
>>>>> /*
>>>>> * This file implements an out-of-SSA pass as described in
>>>>> "Revisiting
>>>>> @@ -181,7 +182,7 @@ merge_merge_sets(merge_set *a, merge_set *b)
>>>>> static bool
>>>>> merge_sets_interfere(merge_set *a, merge_set *b)
>>>>> {
>>>>> - merge_node *dom[a->size + b->size];
>>>>> + merge_node **dom = alloca((a->size + b->size) * sizeof *dom);
>>>>> int dom_idx = -1;
>>>>>
>>>>> struct exec_node *an = exec_list_get_head(&a->nodes);
>>>>> @@ -673,21 +674,21 @@ resolve_parallel_copy(nir_parallel_copy_instr
>>>>> *pcopy,
>>>>> }
>>>>>
>>>>> /* The register/source corresponding to the given index */
>>>>> - nir_src values[num_copies * 2];
>>>>> - memset(values, 0, sizeof values);
>>>>> + nir_src *values = alloca(num_copies * 2 * sizeof *values);
>>>>> + memset(values, 0, num_copies * 2 * sizeof *values);
>>>>>
>>>>> /* The current location of a given piece of data */
>>>>> - int loc[num_copies * 2];
>>>>> + int *loc = alloca(num_copies * 2 * sizeof *loc);
>>>>>
>>>>> /* The piece of data that the given piece of data is to be copied
>>>>> from */
>>>>> - int pred[num_copies * 2];
>>>>> + int *pred = alloca(num_copies * 2 * sizeof *pred);
>>>>>
>>>>> /* Initialize loc and pred. We will use -1 for "null" */
>>>>> - memset(loc, -1, sizeof loc);
>>>>> - memset(pred, -1, sizeof pred);
>>>>> + memset(loc, -1, num_copies * 2 * sizeof *loc);
>>>>> + memset(pred, -1, num_copies * 2 * sizeof *pred);
>>>>>
>>>>> /* The destinations we have yet to properly fill */
>>>>> - int to_do[num_copies * 2];
>>>>> + int *to_do = alloca(num_copies * 2 * sizeof *to_do);
>>>>> int to_do_idx = -1;
>>>>>
>>>>> /* Now we set everything up:
>>>>> @@ -737,7 +738,7 @@ resolve_parallel_copy(nir_parallel_copy_instr
>>>>> *pcopy,
>>>>> }
>>>>>
>>>>> /* Currently empty destinations we can go ahead and fill */
>>>>> - int ready[num_copies * 2];
>>>>> + int *ready = alloca(num_copies * 2 * sizeof *ready);
>>>>> int ready_idx = -1;
>>>>>
>>>>> /* Mark the ones that are ready for copying. We know an index
>>>>> is a
>>>>> diff --git a/src/glsl/nir/nir_live_variables.c
>>>>> b/src/glsl/nir/nir_live_variables.c
>>>>> index 7402dc0..b57ca3a 100644
>>>>> --- a/src/glsl/nir/nir_live_variables.c
>>>>> +++ b/src/glsl/nir/nir_live_variables.c
>>>>> @@ -26,6 +26,7 @@
>>>>>
>>>>> #include "nir.h"
>>>>> #include "nir_worklist.h"
>>>>> +#include "c99_alloca.h"
>>>>>
>>>>> /*
>>>>> * Basic liveness analysis. This works only in SSA form.
>>>>> @@ -130,8 +131,8 @@ static bool
>>>>> propagate_across_edge(nir_block *pred, nir_block *succ,
>>>>> struct live_variables_state *state)
>>>>> {
>>>>> - BITSET_WORD live[state->bitset_words];
>>>>> - memcpy(live, succ->live_in, sizeof live);
>>>>> + BITSET_WORD *live = alloca(state->bitset_words * sizeof *live);
>>>>> + memcpy(live, succ->live_in, state->bitset_words * sizeof *live);
>>>>>
>>>>> nir_foreach_instr(succ, instr) {
>>>>> if (instr->type != nir_instr_type_phi)
>>>>> diff --git a/src/glsl/nir/nir_lower_vars_to_ssa.c
>>>>> b/src/glsl/nir/nir_lower_vars_to_ssa.c
>>>>> index 8af7530..f54d1b7 100644
>>>>> --- a/src/glsl/nir/nir_lower_vars_to_ssa.c
>>>>> +++ b/src/glsl/nir/nir_lower_vars_to_ssa.c
>>>>> @@ -27,6 +27,9 @@
>>>>>
>>>>> #include "nir.h"
>>>>>
>>>>> +#include "c99_alloca.h"
>>>>> +
>>>>> +
>>>>> struct deref_node {
>>>>> struct deref_node *parent;
>>>>> const struct glsl_type *type;
>>>>> @@ -899,8 +902,8 @@ rename_variables_block(nir_block *block, struct
>>>>> lower_variables_state *state)
>>>>> static void
>>>>> insert_phi_nodes(struct lower_variables_state *state)
>>>>> {
>>>>> - unsigned work[state->impl->num_blocks];
>>>>> - unsigned has_already[state->impl->num_blocks];
>>>>> + unsigned *work = alloca(state->impl->num_blocks * sizeof *work);
>>>>> + unsigned *has_already = alloca(state->impl->num_blocks * sizeof
>>>>> *has_already);
>>>>>
>>>>> /*
>>>>> * Since the work flags already prevent us from inserting a node
>>>>> that has
>>>>> @@ -910,10 +913,10 @@ insert_phi_nodes(struct lower_variables_state
>>>>> *state)
>>>>> * function. So all we need to handle W is an array and a pointer
>>>>> to the
>>>>> * next element to be inserted and the next element to be
>>>>> removed.
>>>>> */
>>>>> - nir_block *W[state->impl->num_blocks];
>>>>> + nir_block **W = alloca(state->impl->num_blocks * sizeof *W);
>>>>>
>>>>> - memset(work, 0, sizeof work);
>>>>> - memset(has_already, 0, sizeof has_already);
>>>>> + memset(work, 0, state->impl->num_blocks * sizeof *work);
>>>>> + memset(has_already, 0, state->impl->num_blocks * sizeof
>>>>> *has_already);
>>>>>
>>>>> unsigned w_start, w_end;
>>>>> unsigned iter_count = 0;
>>>>>
>>>>>
>>>> Looks OK to me.
>>>>
>>>> One thing I might have done would be instead of:
>>>>
>>>> unsigned *work = alloca(state->impl->num_blocks * sizeof *work);
>>>> ...
>>>> memset(work, 0, state->impl->num_blocks * sizeof *work);
>>>>
>>>> do
>>>>
>>>> const int work_size = state->impl->num_blocks * sizeof *work;
>>>> unsigned *work = alloca(work_size);
>>>> ...
>>>> memset(work, 0, work_size);
>>>>
>>>>
>>>> AFAIK, there's no zeroing version of alloca().
>>>>
>>>
>>> It occurs to me that this may be the only reasonable use-case in all
>>> history of memset returning the pointer that you pass to it:
>>>
>>> unsigned *work = memset(alloca(work_size), 0, work_size);
>>>
>>
>> That's cool!
>>
>
> Yes, indeed, that can save another source line.
>
>
> FWIW, I also tried to prototype a few macros for dealing with VLAs:
>
> http://cgit.freedesktop.org/~jrfonseca/mesa/commit/?h=nir-vla
>
> On one hand, they save quite a bit of typing, even compared with vanilla
> C99 VLAs. On the other hand, being macros it's always a bit magical and
> tricky to read..
>
I'm OK with the macro magic. I have two qualms, however. First, I'm not
sure I like the fact that it defines a second size variable behind your
back. Second, I'd like to keep it to one line if we can and require the
user to provide the semicolon. Since we already have the type from the
user, this shouldn't be hard as we can do
_type *_name = alloca((_length) * sizeof(_type))
Then we don't have to worry about when the variable is declared vs. when
the sizeof happens. Also, hiding it in a macro means that we could do
_type _name[_length]
for GCC/clang builds if we wanted to.
--Jason
>
> I only prototyped this on a single source file. But if you like this
> direction I can move it to a header and use it on all places in NIR where
> VLAs are needed.
>
>
> Let me know what you guys want to do.
>
>
> Jose
>
>
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>
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