nir: move to compiler/

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Matt Turner <mattst88@gmail.com>
Acked-by: Jose Fonseca <jfonseca@vmware.com>

src/compiler/nir/nir_opt_remove_phis.c

@@ -0,0 +1,130 @@
+/*
+ * Copyright © 2015 Connor Abbott
+ *
+ * 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:
+ *    Connor Abbott (cwabbott0@gmail.com)
+ *
+ */
+
+#include "nir.h"
+
+/*
+ * This is a pass for removing phi nodes that look like:
+ * a = phi(b, b, b, ...)
+ *
+ * Note that we can't ignore undef sources here, or else we may create a
+ * situation where the definition of b isn't dominated by its uses. We're
+ * allowed to do this since the definition of b must dominate all of the
+ * phi node's predecessors, which means it must dominate the phi node as well
+ * as all of the phi node's uses. In essence, the phi node acts as a copy
+ * instruction. b can't be another phi node in the same block, since the only
+ * time when phi nodes can source other phi nodes defined in the same block is
+ * at the loop header, and in that case one of the sources of the phi has to
+ * be from before the loop and that source can't be b.
+ */
+
+static bool
+remove_phis_block(nir_block *block, void *state)
+{
+   bool *progress = state;
+
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type != nir_instr_type_phi)
+         break;
+
+      nir_phi_instr *phi = nir_instr_as_phi(instr);
+
+      nir_ssa_def *def = NULL;
+      bool srcs_same = true;
+
+      nir_foreach_phi_src(phi, src) {
+         assert(src->src.is_ssa);
+
+         /* For phi nodes at the beginning of loops, we may encounter some
+          * sources from backedges that point back to the destination of the
+          * same phi, i.e. something like:
+          *
+          * a = phi(a, b, ...)
+          *
+          * We can safely ignore these sources, since if all of the normal
+          * sources point to the same definition, then that definition must
+          * still dominate the phi node, and the phi will still always take
+          * the value of that definition.
+          */
+         if (src->src.ssa == &phi->dest.ssa)
+            continue;
+         
+         if (def == NULL) {
+            def  = src->src.ssa;
+         } else {
+            if (src->src.ssa != def) {
+               srcs_same = false;
+               break;
+            }
+         }
+      }
+
+      if (!srcs_same)
+         continue;
+
+      /* We must have found at least one definition, since there must be at
+       * least one forward edge.
+       */
+      assert(def != NULL);
+
+      assert(phi->dest.is_ssa);
+      nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def));
+      nir_instr_remove(instr);
+
+      *progress = true;
+   }
+
+   return true;
+}
+
+static bool
+remove_phis_impl(nir_function_impl *impl)
+{
+   bool progress = false;
+
+   nir_foreach_block(impl, remove_phis_block, &progress);
+
+   if (progress) {
+      nir_metadata_preserve(impl, nir_metadata_block_index |
+                                  nir_metadata_dominance);
+   }
+
+   return progress;
+}
+
+bool
+nir_opt_remove_phis(nir_shader *shader)
+{
+   bool progress = false;
+
+   nir_foreach_function(shader, function)
+      if (function->impl)
+         progress = remove_phis_impl(function->impl) || progress;
+
+   return progress;
+}
+