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 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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