nir: move to compiler/

Signed-off-by: Emil Velikov <[email protected]>
Acked-by: Matt Turner <[email protected]>
Acked-by: Jose Fonseca <[email protected]>

1 files changed, 297 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_liveness.c b/src/compiler/nir/nir_liveness.c
new file mode 100644
index 00000000000..05f79d7bc61
--- /dev/null
+++ b/src/compiler/nir/nir_liveness.c
@@ -0,0 +1,297 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * 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.
+ *
+ * Authors:
+ *    Jason Ekstrand ([email protected])
+ */
+
+#include "nir.h"
+#include "nir_worklist.h"
+#include "nir_vla.h"
+
+/*
+ * Basic liveness analysis.  This works only in SSA form.
+ *
+ * This liveness pass treats phi nodes as being melded to the space between
+ * blocks so that the destinations of a phi are in the livein of the block
+ * in which it resides and the sources are in the liveout of the
+ * corresponding block.  By formulating the liveness information in this
+ * way, we ensure that the definition of any variable dominates its entire
+ * live range.  This is true because the only way that the definition of an
+ * SSA value may not dominate a use is if the use is in a phi node and the
+ * uses in phi no are in the live-out of the corresponding predecessor
+ * block but not in the live-in of the block containing the phi node.
+ */
+
+struct live_ssa_defs_state {
+   unsigned num_ssa_defs;
+   unsigned bitset_words;
+
+   nir_block_worklist worklist;
+};
+
+static bool
+index_ssa_def(nir_ssa_def *def, void *void_state)
+{
+   struct live_ssa_defs_state *state = void_state;
+
+   if (def->parent_instr->type == nir_instr_type_ssa_undef)
+      def->live_index = 0;
+   else
+      def->live_index = state->num_ssa_defs++;
+
+   return true;
+}
+
+static bool
+index_ssa_definitions_block(nir_block *block, void *state)
+{
+   nir_foreach_instr(block, instr)
+      nir_foreach_ssa_def(instr, index_ssa_def, state);
+
+   return true;
+}
+
+/* Initialize the liveness data to zero and add the given block to the
+ * worklist.
+ */
+static bool
+init_liveness_block(nir_block *block, void *void_state)
+{
+   struct live_ssa_defs_state *state = void_state;
+
+   block->live_in = reralloc(block, block->live_in, BITSET_WORD,
+                             state->bitset_words);
+   memset(block->live_in, 0, state->bitset_words * sizeof(BITSET_WORD));
+
+   block->live_out = reralloc(block, block->live_out, BITSET_WORD,
+                              state->bitset_words);
+   memset(block->live_out, 0, state->bitset_words * sizeof(BITSET_WORD));
+
+   nir_block_worklist_push_head(&state->worklist, block);
+
+   return true;
+}
+
+static bool
+set_src_live(nir_src *src, void *void_live)
+{
+   BITSET_WORD *live = void_live;
+
+   if (!src->is_ssa)
+      return true;
+
+   if (src->ssa->live_index == 0)
+      return true;   /* undefined variables are never live */
+
+   BITSET_SET(live, src->ssa->live_index);
+
+   return true;
+}
+
+static bool
+set_ssa_def_dead(nir_ssa_def *def, void *void_live)
+{
+   BITSET_WORD *live = void_live;
+
+   BITSET_CLEAR(live, def->live_index);
+
+   return true;
+}
+
+/** Propagates the live in of succ across the edge to the live out of pred
+ *
+ * Phi nodes exist "between" blocks and all the phi nodes at the start of a
+ * block act "in parallel".  When we propagate from the live_in of one
+ * block to the live out of the other, we have to kill any writes from phis
+ * and make live any sources.
+ *
+ * Returns true if updating live out of pred added anything
+ */
+static bool
+propagate_across_edge(nir_block *pred, nir_block *succ,
+                      struct live_ssa_defs_state *state)
+{
+   NIR_VLA(BITSET_WORD, live, state->bitset_words);
+   memcpy(live, succ->live_in, state->bitset_words * sizeof *live);
+
+   nir_foreach_instr(succ, instr) {
+      if (instr->type != nir_instr_type_phi)
+         break;
+      nir_phi_instr *phi = nir_instr_as_phi(instr);
+
+      assert(phi->dest.is_ssa);
+      set_ssa_def_dead(&phi->dest.ssa, live);
+   }
+
+   nir_foreach_instr(succ, instr) {
+      if (instr->type != nir_instr_type_phi)
+         break;
+      nir_phi_instr *phi = nir_instr_as_phi(instr);
+
+      nir_foreach_phi_src(phi, src) {
+         if (src->pred == pred) {
+            set_src_live(&src->src, live);
+            break;
+         }
+      }
+   }
+
+   BITSET_WORD progress = 0;
+   for (unsigned i = 0; i < state->bitset_words; ++i) {
+      progress |= live[i] & ~pred->live_out[i];
+      pred->live_out[i] |= live[i];
+   }
+   return progress != 0;
+}
+
+void
+nir_live_ssa_defs_impl(nir_function_impl *impl)
+{
+   struct live_ssa_defs_state state;
+
+   /* We start at 1 because we reserve the index value of 0 for ssa_undef
+    * instructions.  Those are never live, so their liveness information
+    * can be compacted into a single bit.
+    */
+   state.num_ssa_defs = 1;
+   nir_foreach_block(impl, index_ssa_definitions_block, &state);
+
+   nir_block_worklist_init(&state.worklist, impl->num_blocks, NULL);
+
+   /* We now know how many unique ssa definitions we have and we can go
+    * ahead and allocate live_in and live_out sets and add all of the
+    * blocks to the worklist.
+    */
+   state.bitset_words = BITSET_WORDS(state.num_ssa_defs);
+   nir_foreach_block(impl, init_liveness_block, &state);
+
+   /* We're now ready to work through the worklist and update the liveness
+    * sets of each of the blocks.  By the time we get to this point, every
+    * block in the function implementation has been pushed onto the
+    * worklist in reverse order.  As long as we keep the worklist
+    * up-to-date as we go, everything will get covered.
+    */
+   while (!nir_block_worklist_is_empty(&state.worklist)) {
+      /* We pop them off in the reverse order we pushed them on.  This way
+       * the first walk of the instructions is backwards so we only walk
+       * once in the case of no control flow.
+       */
+      nir_block *block = nir_block_worklist_pop_head(&state.worklist);
+
+      memcpy(block->live_in, block->live_out,
+             state.bitset_words * sizeof(BITSET_WORD));
+
+      nir_if *following_if = nir_block_get_following_if(block);
+      if (following_if)
+         set_src_live(&following_if->condition, block->live_in);
+
+      nir_foreach_instr_reverse(block, instr) {
+         /* Phi nodes are handled seperately so we want to skip them.  Since
+          * we are going backwards and they are at the beginning, we can just
+          * break as soon as we see one.
+          */
+         if (instr->type == nir_instr_type_phi)
+            break;
+
+         nir_foreach_ssa_def(instr, set_ssa_def_dead, block->live_in);
+         nir_foreach_src(instr, set_src_live, block->live_in);
+      }
+
+      /* Walk over all of the predecessors of the current block updating
+       * their live in with the live out of this one.  If anything has
+       * changed, add the predecessor to the work list so that we ensure
+       * that the new information is used.
+       */
+      struct set_entry *entry;
+      set_foreach(block->predecessors, entry) {
+         nir_block *pred = (nir_block *)entry->key;
+         if (propagate_across_edge(pred, block, &state))
+            nir_block_worklist_push_tail(&state.worklist, pred);
+      }
+   }
+
+   nir_block_worklist_fini(&state.worklist);
+}
+
+static bool
+src_does_not_use_def(nir_src *src, void *def)
+{
+   return !src->is_ssa || src->ssa != (nir_ssa_def *)def;
+}
+
+static bool
+search_for_use_after_instr(nir_instr *start, nir_ssa_def *def)
+{
+   /* Only look for a use strictly after the given instruction */
+   struct exec_node *node = start->node.next;
+   while (!exec_node_is_tail_sentinel(node)) {
+      nir_instr *instr = exec_node_data(nir_instr, node, node);
+      if (!nir_foreach_src(instr, src_does_not_use_def, def))
+         return true;
+      node = node->next;
+   }
+   return false;
+}
+
+/* Returns true if def is live at instr assuming that def comes before
+ * instr in a pre DFS search of the dominance tree.
+ */
+static bool
+nir_ssa_def_is_live_at(nir_ssa_def *def, nir_instr *instr)
+{
+   if (BITSET_TEST(instr->block->live_out, def->live_index)) {
+      /* Since def dominates instr, if def is in the liveout of the block,
+       * it's live at instr
+       */
+      return true;
+   } else {
+      if (BITSET_TEST(instr->block->live_in, def->live_index) ||
+          def->parent_instr->block == instr->block) {
+         /* In this case it is either live coming into instr's block or it
+          * is defined in the same block.  In this case, we simply need to
+          * see if it is used after instr.
+          */
+         return search_for_use_after_instr(instr, def);
+      } else {
+         return false;
+      }
+   }
+}
+
+bool
+nir_ssa_defs_interfere(nir_ssa_def *a, nir_ssa_def *b)
+{
+   if (a->parent_instr == b->parent_instr) {
+      /* Two variables defined at the same time interfere assuming at
+       * least one isn't dead.
+       */
+      return true;
+   } else if (a->live_index == 0 || b->live_index == 0) {
+      /* If either variable is an ssa_undef, then there's no interference */
+      return false;
+   } else if (a->live_index < b->live_index) {
+      return nir_ssa_def_is_live_at(a, b->parent_instr);
+   } else {
+      return nir_ssa_def_is_live_at(b, a->parent_instr);
+   }
+}