lima/gpir: Optimize conditional break/continue

Optimize the result of a conditional break/continue. In NIR something
like:

loop {
   ...
   if (cond)
      continue;

would get lowered to:

block_0:
...
block_1:
branch_cond !cond block_3
block_2:
branch_uncond block_0
block_3:
...

We recognize the conditional branch skipping over the unconditional
branch, and turn it into:

block_0:
...
block_1:
branch_cond cond block_0
block_2:
block_3:

Reviewed-by: Vasily Khoruzhick <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4125>

4 files changed, 126 insertions, 0 deletions

diff --git a/src/gallium/drivers/lima/ir/gp/gpir.h b/src/gallium/drivers/lima/ir/gp/gpir.h
index 26d0fd9ffa7..26cbb099a94 100644
--- a/src/gallium/drivers/lima/ir/gp/gpir.h
+++ b/src/gallium/drivers/lima/ir/gp/gpir.h
@@ -475,6 +475,7 @@ void gpir_instr_print_prog(gpir_compiler *comp);
 
 bool gpir_codegen_acc_same_op(gpir_op op1, gpir_op op2);
 
+bool gpir_optimize(gpir_compiler *comp);
 bool gpir_pre_rsched_lower_prog(gpir_compiler *comp);
 bool gpir_reduce_reg_pressure_schedule_prog(gpir_compiler *comp);
 bool gpir_regalloc_prog(gpir_compiler *comp);
diff --git a/src/gallium/drivers/lima/ir/gp/nir.c b/src/gallium/drivers/lima/ir/gp/nir.c
index 9916a057656..223db082424 100644
--- a/src/gallium/drivers/lima/ir/gp/nir.c
+++ b/src/gallium/drivers/lima/ir/gp/nir.c
@@ -469,6 +469,9 @@ bool gpir_compile_nir(struct lima_vs_shader_state *prog, struct nir_shader *nir,
    /* increase for viewport uniforms */
    comp->constant_base += GPIR_VECTOR_SSA_NUM;
 
+   if (!gpir_optimize(comp))
+      goto err_out0;
+
    if (!gpir_pre_rsched_lower_prog(comp))
       goto err_out0;
 
diff --git a/src/gallium/drivers/lima/ir/gp/optimize.c b/src/gallium/drivers/lima/ir/gp/optimize.c
new file mode 100644
index 00000000000..db4adfa5503
--- /dev/null
+++ b/src/gallium/drivers/lima/ir/gp/optimize.c
@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2019 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, sub license,
+ * 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 NON-INFRINGEMENT. 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 "gpir.h"
+
+/* Here we perform a few optimizations that can't currently be done in NIR:
+ *
+ * - Optimize the result of a conditional break/continue. In NIR something
+ *   like:
+ *
+ * loop {
+ *    ...
+ *    if (cond)
+ *       continue;
+ *
+ * would get lowered to:
+ *
+ * block_0:
+ * ...
+ * block_1:
+ * branch_cond !cond block_3
+ * block_2:
+ * branch_uncond block_0
+ * block_3:
+ * ...
+ *
+ *   We recognize the conditional branch skipping over the unconditional
+ *   branch, and turn it into:
+ *
+ * block_0:
+ * ...
+ * block_1:
+ * branch_cond cond block_0
+ * block_2:
+ * block_3:
+ * ...
+ */
+
+static void
+optimize_branches(gpir_compiler *comp)
+{
+   list_for_each_entry(gpir_block, block, &comp->block_list, list) {
+      /* Look for a block with a single unconditional branch. */
+      if (!list_is_singular(&block->node_list))
+         continue;
+
+      gpir_node *node = list_first_entry(&block->node_list, gpir_node, list);
+      if (node->op != gpir_op_branch_uncond)
+         continue;
+
+      gpir_block *target = gpir_node_to_branch(node)->dest;
+
+      /* Find the previous block */
+      if (block->list.prev == &comp->block_list)
+         continue;
+
+      gpir_block *prev_block = LIST_ENTRY(gpir_block, block->list.prev, list);
+      if (list_is_empty(&prev_block->node_list))
+         continue;
+
+      /* Previous block must end with a conditional branch */
+      gpir_node *prev_block_last =
+         list_last_entry(&prev_block->node_list, gpir_node, list);
+      if (prev_block_last->op != gpir_op_branch_cond)
+         continue;
+
+      /* That branch must branch to the block after this */
+      gpir_branch_node *prev_branch = gpir_node_to_branch(prev_block_last);
+      gpir_block *prev_target = prev_branch->dest;
+
+      if (&prev_target->list != block->list.next)
+         continue;
+
+      /* Hooray! Invert the conditional branch and change the target */
+      gpir_alu_node *cond = gpir_node_create(prev_block, gpir_op_not);
+      cond->children[0] = prev_branch->cond;
+      cond->num_child = 1;
+      gpir_node_add_dep(&cond->node, cond->children[0], GPIR_DEP_INPUT);
+      list_addtail(&cond->node.list, &prev_block_last->list);
+      gpir_node_insert_child(prev_block_last, prev_branch->cond, &cond->node);
+      prev_branch->dest = target;
+      prev_block->successors[1] = target;
+
+      /* Delete the branch */
+      list_del(&node->list);
+      block->successors[0] = LIST_ENTRY(gpir_block, block->list.next, list);
+   }
+}
+
+bool
+gpir_optimize(gpir_compiler *comp)
+{
+   optimize_branches(comp);
+
+   gpir_debug("after optimization\n");
+   gpir_node_print_prog_seq(comp);
+
+   return true;
+}
+
diff --git a/src/gallium/drivers/lima/meson.build b/src/gallium/drivers/lima/meson.build
index c0cec6ad2ae..23766a8a4f3 100644
--- a/src/gallium/drivers/lima/meson.build
+++ b/src/gallium/drivers/lima/meson.build
@@ -31,6 +31,7 @@ files_lima = files(
   'ir/gp/reduce_scheduler.c',
   'ir/gp/regalloc.c',
   'ir/gp/disasm.c',
+  'ir/gp/optimize.c',
 
   'ir/pp/ppir.h',
   'ir/pp/nir.c',