Mesa (main): ir3: Add pass to remove unreachable blocks
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Fri Aug 20 10:57:10 UTC 2021
Module: Mesa
Branch: main
Commit: 2768a35e416ed8914989474d320de3227a5ecd84
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=2768a35e416ed8914989474d320de3227a5ecd84
Author: Connor Abbott <cwabbott0 at gmail.com>
Date: Wed Jul 21 15:03:21 2021 +0200
ir3: Add pass to remove unreachable blocks
Rather than continue to add special cases for these, just clean them up.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12033>
---
src/freedreno/ir3/ir3.c | 16 ++++
src/freedreno/ir3/ir3.h | 5 ++
src/freedreno/ir3/ir3_compiler_nir.c | 2 +
src/freedreno/ir3/ir3_remove_unreachable.c | 122 +++++++++++++++++++++++++++++
src/freedreno/ir3/meson.build | 1 +
5 files changed, 146 insertions(+)
diff --git a/src/freedreno/ir3/ir3.c b/src/freedreno/ir3/ir3.c
index 1491429c14a..48f9f38cca4 100644
--- a/src/freedreno/ir3/ir3.c
+++ b/src/freedreno/ir3/ir3.c
@@ -393,6 +393,22 @@ ir3_block_remove_predecessor(struct ir3_block *block, struct ir3_block *pred)
}
}
+void
+ir3_block_remove_physical_predecessor(struct ir3_block *block, struct ir3_block *pred)
+{
+ for (unsigned i = 0; i < block->physical_predecessors_count; i++) {
+ if (block->physical_predecessors[i] == pred) {
+ if (i < block->predecessors_count - 1) {
+ block->physical_predecessors[i] =
+ block->physical_predecessors[block->predecessors_count - 1];
+ }
+
+ block->physical_predecessors_count--;
+ return;
+ }
+ }
+}
+
unsigned
ir3_block_get_pred_index(struct ir3_block *block, struct ir3_block *pred)
{
diff --git a/src/freedreno/ir3/ir3.h b/src/freedreno/ir3/ir3.h
index 723eb6567ed..e0dd870971d 100644
--- a/src/freedreno/ir3/ir3.h
+++ b/src/freedreno/ir3/ir3.h
@@ -615,6 +615,8 @@ void ir3_block_add_physical_predecessor(struct ir3_block *block,
struct ir3_block *pred);
void ir3_block_remove_predecessor(struct ir3_block *block,
struct ir3_block *pred);
+void ir3_block_remove_physical_predecessor(struct ir3_block *block,
+ struct ir3_block *pred);
unsigned ir3_block_get_pred_index(struct ir3_block *block,
struct ir3_block *pred);
@@ -1593,6 +1595,9 @@ unsigned ir3_delay_calc_exact(struct ir3_block *block,
struct ir3_instruction *instr, bool mergedregs);
void ir3_remove_nops(struct ir3 *ir);
+/* unreachable block elimination: */
+bool ir3_remove_unreachable(struct ir3 *ir);
+
/* dead code elimination: */
struct ir3_shader_variant;
bool ir3_dce(struct ir3 *ir, struct ir3_shader_variant *so);
diff --git a/src/freedreno/ir3/ir3_compiler_nir.c b/src/freedreno/ir3/ir3_compiler_nir.c
index b634eb50e96..16be6e1f810 100644
--- a/src/freedreno/ir3/ir3_compiler_nir.c
+++ b/src/freedreno/ir3/ir3_compiler_nir.c
@@ -4135,6 +4135,8 @@ ir3_compile_shader_nir(struct ir3_compiler *compiler,
ir3_debug_print(ir, "AFTER: nir->ir3");
ir3_validate(ir);
+ IR3_PASS(ir, ir3_remove_unreachable);
+
IR3_PASS(ir, ir3_array_to_ssa);
do {
diff --git a/src/freedreno/ir3/ir3_remove_unreachable.c b/src/freedreno/ir3/ir3_remove_unreachable.c
new file mode 100644
index 00000000000..c598d9f2e59
--- /dev/null
+++ b/src/freedreno/ir3/ir3_remove_unreachable.c
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2021 Valve 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 "ir3.h"
+
+/* Sometimes we can get unreachable blocks from NIR. In particular this happens
+ * for blocks after an if where both sides end in a break/continue. These blocks
+ * are then reachable only via the physical CFG. This pass deletes these blocks
+ * and reroutes the physical edge past it.
+ */
+
+static void
+delete_block(struct ir3 *ir, struct ir3_block *block)
+{
+ struct ir3_instruction *end = NULL;
+ foreach_instr (instr, &block->instr_list) {
+ if (instr->opc == OPC_END) {
+ end = instr;
+ break;
+ }
+ }
+
+ /* The end block can be legitimately unreachable if the shader only exits via
+ * discarding. ir3_legalize will then insert a branch to the end. Keep the
+ * block around but delete all the other instructions and make the end not
+ * take any sources, so that we don't have any dangling references to other
+ * unreachable blocks.
+ */
+ if (end) {
+ foreach_instr_safe (instr, &block->instr_list) {
+ if (instr != end)
+ list_delinit(&instr->node);
+ }
+ end->srcs_count = 0;
+ return;
+ }
+
+ for (unsigned i = 0; i < 2; i++) {
+ struct ir3_block *succ = block->successors[i];
+ if (!succ)
+ continue;
+
+ unsigned pred_idx = ir3_block_get_pred_index(succ, block);
+
+ /* If this isn't the last predecessor, we swap it with the last before
+ * removing it.
+ */
+ bool swap_pred = pred_idx != succ->predecessors_count - 1;
+
+ foreach_instr (phi, &succ->instr_list) {
+ if (phi->opc != OPC_META_PHI)
+ break;
+
+ if (swap_pred)
+ phi->srcs[pred_idx] = phi->srcs[phi->srcs_count - 1];
+ phi->srcs_count--;
+ }
+ if (swap_pred) {
+ succ->predecessors[pred_idx] =
+ succ->predecessors[succ->predecessors_count - 1];
+ }
+ succ->predecessors_count--;
+ }
+
+ for (unsigned i = 0; i < 2; i++) {
+ struct ir3_block *succ = block->physical_successors[i];
+ if (!succ)
+ continue;
+
+ ir3_block_remove_physical_predecessor(succ, block);
+ }
+
+ if (block->physical_predecessors_count != 0) {
+ /* There should be only one physical predecessor, for the fallthrough
+ * edge.
+ */
+ assert(block->physical_predecessors_count == 1);
+ struct ir3_block *pred = block->physical_predecessors[0];
+ assert(block->node.next != &ir->block_list);
+ struct ir3_block *next = LIST_ENTRY(struct ir3_block, block->node.next, node);
+ if (pred->physical_successors[1] == block)
+ pred->physical_successors[1] = next;
+ else
+ pred->physical_successors[0] = next;
+ ir3_block_add_physical_predecessor(next, pred);
+ }
+}
+
+bool
+ir3_remove_unreachable(struct ir3 *ir)
+{
+ bool progress = false;
+ foreach_block_safe (block, &ir->block_list) {
+ if (block != ir3_start_block(ir) && block->predecessors_count == 0) {
+ delete_block(ir, block);
+ list_del(&block->node);
+ progress = true;
+ }
+ }
+
+ return progress;
+}
diff --git a/src/freedreno/ir3/meson.build b/src/freedreno/ir3/meson.build
index 1bf9847ad95..40bdb26194d 100644
--- a/src/freedreno/ir3/meson.build
+++ b/src/freedreno/ir3/meson.build
@@ -105,6 +105,7 @@ libfreedreno_ir3_files = files(
'ir3_ra.c',
'ir3_ra.h',
'ir3_ra_validate.c',
+ 'ir3_remove_unreachable.c',
'ir3_sched.c',
'ir3_shader.c',
'ir3_shader.h',
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