nir: Implement a nir_sweep() pass.

This pass performs a mark and sweep pass over a nir_shader's associated
memory - anything still connected to the program will be kept, and any
dead memory we dropped on the floor will be freed.

The expectation is that this will be called when finished building and
optimizing the shader.  However, it's also fine to call it earlier, and
many times, to free up memory earlier.

v2: (feedback from Jason Ekstrand)
- Skip sweeping impl->start_block, as it's already in the CF list.
- Don't sweep SSA defs (they're owned by their defining instruction)
- Don't steal phi sources (they're owned by nir_phi_instr).
- Don't steal tex->src (it's owned by the tex_inst itself)
- Don't sweep dereference chains (top-level dereferences are owned by
  the instruction; sub-dereferences are owned by the parent deref).
- Don't sweep sources and destinations (SSA defs are handled as part of
  the defining instruction, and registers are handled as part of
  function implementations).
- Just steal instructions; don't walk them (no longer required).

v3: (feedback from Jason Ekstrand)
- Steal indirect sources from nir_src/nir_dest.

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Jason Ekstrand <[email protected]>

3 files changed, 175 insertions, 0 deletions

diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index 9bdcb8084de..c471eca23ea 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -59,6 +59,7 @@ NIR_FILES = \
 	nir/nir_search.c \
 	nir/nir_search.h \
 	nir/nir_split_var_copies.c \
+	nir/nir_sweep.c \
 	nir/nir_to_ssa.c \
 	nir/nir_types.h \
 	nir/nir_validate.c \
diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index e6b76844b93..0f72301525e 100644
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1650,6 +1650,8 @@ bool nir_opt_peephole_ffma(nir_shader *shader);
 
 bool nir_opt_remove_phis(nir_shader *shader);
 
+void nir_sweep(nir_shader *shader);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/src/glsl/nir/nir_sweep.c b/src/glsl/nir/nir_sweep.c
new file mode 100644
index 00000000000..d3549756a63
--- /dev/null
+++ b/src/glsl/nir/nir_sweep.c
@@ -0,0 +1,172 @@
+/*
+ * Copyright © 2015 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.
+ */
+
+#include "nir.h"
+
+/**
+ * \file nir_sweep.c
+ *
+ * The nir_sweep() pass performs a mark and sweep pass over a nir_shader's associated
+ * memory - anything still connected to the program will be kept, and any dead memory
+ * we dropped on the floor will be freed.
+ *
+ * The expectation is that drivers should call this when finished compiling the shader
+ * (after any optimization, lowering, and so on).  However, it's also fine to call it
+ * earlier, and even many times, trading CPU cycles for memory savings.
+ */
+
+#define steal_list(mem_ctx, type, list) \
+   foreach_list_typed(type, obj, node, list) { ralloc_steal(mem_ctx, obj); }
+
+static void sweep_cf_node(nir_shader *nir, nir_cf_node *cf_node);
+
+static bool
+sweep_src_indirect(nir_src *src, void *nir)
+{
+   if (!src->is_ssa && src->reg.indirect)
+      ralloc_steal(nir, src->reg.indirect);
+
+   return true;
+}
+
+static bool
+sweep_dest_indirect(nir_dest *dest, void *nir)
+{
+   if (!dest->is_ssa && dest->reg.indirect)
+      ralloc_steal(nir, dest->reg.indirect);
+
+   return true;
+}
+
+static void
+sweep_block(nir_shader *nir, nir_block *block)
+{
+   ralloc_steal(nir, block);
+
+   nir_foreach_instr(block, instr) {
+      ralloc_steal(nir, instr);
+
+      nir_foreach_src(instr, sweep_src_indirect, nir);
+      nir_foreach_dest(instr, sweep_dest_indirect, nir);
+   }
+}
+
+static void
+sweep_if(nir_shader *nir, nir_if *iff)
+{
+   ralloc_steal(nir, iff);
+
+   foreach_list_typed(nir_cf_node, cf_node, node, &iff->then_list) {
+      sweep_cf_node(nir, cf_node);
+   }
+
+   foreach_list_typed(nir_cf_node, cf_node, node, &iff->else_list) {
+      sweep_cf_node(nir, cf_node);
+   }
+}
+
+static void
+sweep_loop(nir_shader *nir, nir_loop *loop)
+{
+   ralloc_steal(nir, loop);
+
+   foreach_list_typed(nir_cf_node, cf_node, node, &loop->body) {
+      sweep_cf_node(nir, cf_node);
+   }
+}
+
+static void
+sweep_cf_node(nir_shader *nir, nir_cf_node *cf_node)
+{
+   switch (cf_node->type) {
+   case nir_cf_node_block:
+      sweep_block(nir, nir_cf_node_as_block(cf_node));
+      break;
+   case nir_cf_node_if:
+      sweep_if(nir, nir_cf_node_as_if(cf_node));
+      break;
+   case nir_cf_node_loop:
+      sweep_loop(nir, nir_cf_node_as_loop(cf_node));
+      break;
+   default:
+      unreachable("Invalid CF node type");
+   }
+}
+
+static void
+sweep_impl(nir_shader *nir, nir_function_impl *impl)
+{
+   ralloc_steal(nir, impl);
+
+   ralloc_steal(nir, impl->params);
+   ralloc_steal(nir, impl->return_var);
+   steal_list(nir, nir_variable, &impl->locals);
+   steal_list(nir, nir_register, &impl->registers);
+
+   foreach_list_typed(nir_cf_node, cf_node, node, &impl->body) {
+      sweep_cf_node(nir, cf_node);
+   }
+
+   sweep_block(nir, impl->end_block);
+
+   /* Wipe out all the metadata, if any. */
+   nir_metadata_preserve(impl, nir_metadata_none);
+}
+
+static void
+sweep_function(nir_shader *nir, nir_function *f)
+{
+   ralloc_steal(nir, f);
+
+   foreach_list_typed(nir_function_overload, overload, node, &f->overload_list) {
+      ralloc_steal(nir, overload);
+      ralloc_steal(nir, overload->params);
+      if (overload->impl)
+         sweep_impl(nir, overload->impl);
+   }
+}
+
+void
+nir_sweep(nir_shader *nir)
+{
+   void *rubbish = ralloc_context(NULL);
+
+   /* First, move ownership of all the memory to a temporary context; assume dead. */
+   ralloc_adopt(rubbish, nir);
+
+   /* Variables and registers are not dead.  Steal them back. */
+   steal_list(nir, nir_variable, &nir->uniforms);
+   steal_list(nir, nir_variable, &nir->inputs);
+   steal_list(nir, nir_variable, &nir->outputs);
+   steal_list(nir, nir_variable, &nir->globals);
+   steal_list(nir, nir_variable, &nir->system_values);
+   steal_list(nir, nir_register, &nir->registers);
+
+   /* Recurse into functions, stealing their contents back. */
+   foreach_list_typed(nir_function, func, node, &nir->functions) {
+      sweep_function(nir, func);
+   }
+
+   /* Free everything we didn't steal back. */
+   ralloc_free(rubbish);
+}