[Mesa-dev] [PATCH 1/2] nir: Use alloca instead of variable length arrays.
Ian Romanick
idr at freedesktop.org
Fri Feb 27 08:10:44 PST 2015
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);
> Reviewed-by: Brian Paul <brianp at vmware.com>
>
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