agx: Add liveness analysis pass

Based on the Panfrost one, scalarized and with some silly things fixed.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11718>

src/asahi/compiler/agx_compiler.h

@@ -322,6 +322,9 @@ typedef struct agx_block {
 
    /* Offset of the block in the emitted binary */
    off_t offset;
+
+   /** Available for passes to use for metadata */
+   uint8_t pass_flags;
 } agx_block;
 
 typedef struct {
@@ -346,6 +349,9 @@ typedef struct {
    /* Has r0l been zeroed yet due to control flow? */
    bool any_cf;
 
+   /** Computed metadata */
+   bool has_liveness;
+
    /* Number of nested control flow structures within the innermost loop. Since
     * NIR is just loop and if-else, this is the number of nested if-else
     * statements in the loop */
@@ -602,4 +608,7 @@ void agx_dce(agx_context *ctx);
 void agx_ra(agx_context *ctx);
 void agx_pack_binary(agx_context *ctx, struct util_dynarray *emission);
 
+void agx_compute_liveness(agx_context *ctx);
+void agx_liveness_ins_update(BITSET_WORD *live, agx_instr *I);
+
 #endif

src/asahi/compiler/agx_liveness.c

@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2021 Alyssa Rosenzweig
+ * Copyright (C) 2019-2020 Collabora, Ltd.
+ *
+ * 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, sublicense,
+ * 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 NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS 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.
+ */
+
+#include "agx_compiler.h"
+#include "util/u_memory.h"
+#include "util/list.h"
+#include "util/set.h"
+
+/* Liveness analysis is a backwards-may dataflow analysis pass. Within a block,
+ * we compute live_out from live_in. The intrablock pass is linear-time. It
+ * returns whether progress was made. */
+
+/* live_in[s] = GEN[s] + (live_out[s] - KILL[s]) */
+
+void
+agx_liveness_ins_update(BITSET_WORD *live, agx_instr *I)
+{
+   agx_foreach_dest(I, d) {
+      if (I->dest[d].type == AGX_INDEX_NORMAL)
+         BITSET_CLEAR(live, I->dest[d].value);
+   }
+
+   agx_foreach_src(I, s) {
+      if (I->src[s].type == AGX_INDEX_NORMAL)
+         BITSET_SET(live, I->src[s].value);
+   }
+}
+
+static bool
+liveness_block_update(agx_block *blk, unsigned words)
+{
+   bool progress = false;
+
+   /* live_out[s] = sum { p in succ[s] } ( live_in[p] ) */
+   agx_foreach_successor(blk, succ) {
+      for (unsigned i = 0; i < words; ++i)
+         blk->live_out[i] |= succ->live_in[i];
+   }
+
+   /* live_in is live_out after iteration */
+   BITSET_WORD *live = ralloc_array(blk, BITSET_WORD, words);
+   memcpy(live, blk->live_out, words * sizeof(BITSET_WORD));
+
+   agx_foreach_instr_in_block_rev(blk, I)
+      agx_liveness_ins_update(live, I);
+
+   /* To figure out progress, diff live_in */
+   for (unsigned i = 0; i < words; ++i)
+      progress |= (blk->live_in[i] != live[i]);
+
+   ralloc_free(blk->live_in);
+   blk->live_in = live;
+
+   return progress;
+}
+
+/* Globally, liveness analysis uses a fixed-point algorithm based on a
+ * worklist. We initialize a work list with the exit block. We iterate the work
+ * list to compute live_in from live_out for each block on the work list,
+ * adding the predecessors of the block to the work list if we made progress.
+ */
+
+void
+agx_compute_liveness(agx_context *ctx)
+{
+   if (ctx->has_liveness)
+      return;
+
+   /* Set of agx_block */
+   struct set *work_list = _mesa_set_create(NULL, _mesa_hash_pointer,
+                                                  _mesa_key_pointer_equal);
+
+   /* Free any previous liveness, and allocate */
+   unsigned words = BITSET_WORDS(ctx->alloc);
+
+   agx_foreach_block(ctx, block) {
+      if (block->live_in)
+         ralloc_free(block->live_in);
+
+      if (block->live_out)
+         ralloc_free(block->live_out);
+
+      block->pass_flags = false;
+      block->live_in = rzalloc_array(block, BITSET_WORD, words);
+      block->live_out = rzalloc_array(block, BITSET_WORD, words);
+   }
+
+   /* Initialize the work list with the exit block */
+   struct set_entry *cur = _mesa_set_add(work_list, agx_exit_block(ctx));
+
+   /* Iterate the work list */
+   do {
+      /* Pop off a block */
+      agx_block *blk = (struct agx_block *) cur->key;
+      _mesa_set_remove(work_list, cur);
+
+      /* Update its liveness information */
+      bool progress = liveness_block_update(blk, words);
+
+      /* If we made progress, we need to process the predecessors */
+
+      if (progress || !blk->pass_flags) {
+         agx_foreach_predecessor(blk, pred)
+            _mesa_set_add(work_list, pred);
+      }
+
+      /* Use pass flags to communicate that we've visited this block */
+      blk->pass_flags = true;
+   } while((cur = _mesa_set_next_entry(work_list, NULL)) != NULL);
+
+   _mesa_set_destroy(work_list, NULL);
+
+   ctx->has_liveness = true;
+}

src/asahi/compiler/meson.build

@@ -22,6 +22,7 @@
 libasahi_agx_files = files(
   'agx_compile.c',
   'agx_dce.c',
+  'agx_liveness.c',
   'agx_pack.c',
   'agx_print.c',
   'agx_optimizer.c',