[Mesa-dev] [PATCH 2/3] nir: add conditional discard optimisation

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

This is ported from GLSL and converts

if (cond)
	discard;

into
discard_if(cond);

This removes a block, but also is needed by radv
to workaround a bug in the LLVM backend.

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 src/compiler/Makefile.sources                  |  1 +
 src/compiler/nir/nir.h                         |  1 +
 src/compiler/nir/nir_opt_conditional_discard.c | 88 ++++++++++++++++++++++++++
 3 files changed, 90 insertions(+)
 create mode 100644 src/compiler/nir/nir_opt_conditional_discard.c

diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index 669c499..b710cbd 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -228,6 +228,7 @@ NIR_FILES = \
 	nir/nir_metadata.c \
 	nir/nir_move_vec_src_uses_to_dest.c \
 	nir/nir_normalize_cubemap_coords.c \
+	nir/nir_opt_conditional_discard.c \
 	nir/nir_opt_constant_folding.c \
 	nir/nir_opt_copy_propagate.c \
 	nir/nir_opt_cse.c \
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 9264763..caff7a6 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2531,6 +2531,7 @@ bool nir_opt_remove_phis(nir_shader *shader);
 
 bool nir_opt_undef(nir_shader *shader);
 
+bool nir_opt_conditional_discard(nir_shader *shader);
 void nir_sweep(nir_shader *shader);
 
 nir_intrinsic_op nir_intrinsic_from_system_value(gl_system_value val);
diff --git a/src/compiler/nir/nir_opt_conditional_discard.c b/src/compiler/nir/nir_opt_conditional_discard.c
new file mode 100644
index 0000000..dde93df
--- /dev/null
+++ b/src/compiler/nir/nir_opt_conditional_discard.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright © 2016 Red Hat
+ *
+ * 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"
+#include "nir_builder.h"
+
+/** @file nir_opt_conditional_discard.c
+ *
+ * Handles optimization of lowering if (cond) discard to discard_if(cond).
+ */
+
+static bool
+nir_opt_conditional_discard_block(nir_block *block, void *mem_ctx)
+{
+   if (nir_cf_node_is_first(&block->cf_node))
+      return false;
+
+   nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
+   if (prev_node->type != nir_cf_node_if)
+      return false;
+
+   nir_if *if_stmt = nir_cf_node_as_if(prev_node);
+   nir_block *then_block = nir_if_first_then_block(if_stmt);
+   nir_block *else_block = nir_if_first_else_block(if_stmt);
+
+   if (else_block) {
+      if (!exec_list_is_empty(&else_block->instr_list))
+	 return false;
+   }
+
+   if (nir_if_last_then_block(if_stmt) != then_block)
+      return false;
+
+   nir_foreach_instr(instr, then_block) {
+      if (instr->type != nir_instr_type_intrinsic)
+	 return false;
+
+      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+      if (intrin->intrinsic != nir_intrinsic_discard)
+	 return false;
+
+      nir_intrinsic_instr *discard_if = nir_intrinsic_instr_create(mem_ctx, nir_intrinsic_discard_if);
+      nir_src_copy(&discard_if->src[0], &if_stmt->condition, discard_if);
+
+      nir_instr_insert_before_cf(prev_node, &discard_if->instr);
+      nir_instr_remove(&intrin->instr);
+      nir_cf_node_remove(&if_stmt->cf_node);
+      break;
+   }
+
+   return false;
+}
+
+bool
+nir_opt_conditional_discard(nir_shader *shader)
+{
+   bool progress = false;
+
+   nir_foreach_function(function, shader) {
+      if (function->impl) {
+	 void *mem_ctx = ralloc_parent(function->impl);
+         nir_foreach_block_safe(block, function->impl) {
+	    progress |= nir_opt_conditional_discard_block(block, mem_ctx);
+	 }
+      }
+   }
+   return progress;
+}
-- 
2.7.4