freedreno/ir3: add post-scheduler cp pass

A pass to eliminate extra mov's from an array.  We need to do this after
scheduling so we know that there are not any potentially conflicting
array writes between the original `mov` and it's use(s).

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2124
Signed-off-by: Rob Clark <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5280>

5 files changed, 223 insertions, 0 deletions

diff --git a/src/freedreno/Makefile.sources b/src/freedreno/Makefile.sources
index 997d4311aa3..c24f7064339 100644
--- a/src/freedreno/Makefile.sources
+++ b/src/freedreno/Makefile.sources
@@ -28,6 +28,7 @@ ir3_SOURCES := \
 	ir3/ir3_context.c \
 	ir3/ir3_context.h \
 	ir3/ir3_cp.c \
+	ir3/ir3_cp_postsched.c \
 	ir3/ir3_cf.c \
 	ir3/ir3_dce.c \
 	ir3/ir3_delay.c \
diff --git a/src/freedreno/ir3/ir3.h b/src/freedreno/ir3/ir3.h
index 1d37afe0ad6..39056b47a25 100644
--- a/src/freedreno/ir3/ir3.h
+++ b/src/freedreno/ir3/ir3.h
@@ -1304,6 +1304,7 @@ bool ir3_cf(struct ir3 *ir);
 
 /* copy-propagate: */
 bool ir3_cp(struct ir3 *ir, struct ir3_shader_variant *so);
+bool ir3_cp_postsched(struct ir3 *ir);
 
 /* group neighbors and insert mov's to resolve conflicts: */
 bool ir3_group(struct ir3 *ir);
diff --git a/src/freedreno/ir3/ir3_compiler_nir.c b/src/freedreno/ir3/ir3_compiler_nir.c
index 27018683aff..f52e9570b65 100644
--- a/src/freedreno/ir3/ir3_compiler_nir.c
+++ b/src/freedreno/ir3/ir3_compiler_nir.c
@@ -3639,6 +3639,11 @@ ir3_compile_shader_nir(struct ir3_compiler *compiler,
 
 	ir3_debug_print(ir, "AFTER: ir3_sched");
 
+	if (IR3_PASS(ir, ir3_cp_postsched)) {
+		/* cleanup the result of removing unneeded mov's: */
+		while (IR3_PASS(ir, ir3_dce, so)) {}
+	}
+
 	/* Pre-assign VS inputs on a6xx+ binning pass shader, to align
 	 * with draw pass VS, so binning and draw pass can both use the
 	 * same VBO state.
diff --git a/src/freedreno/ir3/ir3_cp_postsched.c b/src/freedreno/ir3/ir3_cp_postsched.c
new file mode 100644
index 00000000000..f761dc19880
--- /dev/null
+++ b/src/freedreno/ir3/ir3_cp_postsched.c
@@ -0,0 +1,215 @@
+/*
+ * Copyright © 2020 Google, Inc.
+ *
+ * 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 "util/ralloc.h"
+#include "util/u_dynarray.h"
+
+#include "ir3.h"
+
+/**
+ * A bit more extra cleanup after sched pass.  In particular, prior to
+ * instruction scheduling, we can't easily eliminate unneeded mov's
+ * from "arrays", because we don't yet know if there is an intervening
+ * array-write scheduled before the use of the array-read.
+ *
+ * NOTE array is equivalent to nir "registers".. ie. it can be length of
+ * one.  It is basically anything that is not SSA.
+ */
+
+
+/**
+ * Check if any instruction before `use` and after `src` writes to the
+ * specified array.  If `offset` is negative, it is a relative (a0.x)
+ * access and we care about all writes to the array (as we don't know
+ * which array element is read).  Otherwise in the case of non-relative
+ * access, we only have to care about the write to the specified (>= 0)
+ * offset.
+ */
+static bool
+has_conflicting_write(struct ir3_instruction *src,
+		struct ir3_instruction *use,
+		unsigned id, int offset)
+{
+	assert(src->block == use->block);
+
+	/* NOTE that since src and use are in the same block, src by
+	 * definition appears in the block's instr_list before use:
+	 */
+	foreach_instr_rev (instr, &use->node) {
+		if (instr == src)
+			break;
+
+		/* if we are looking at a RELATIV read, we can't move
+		 * it past an a0.x write:
+		 */
+		if ((offset < 0) && (dest_regs(instr) > 0) &&
+				(instr->regs[0]->num == regid(REG_A0, 0)))
+			return true;
+
+		if (!writes_gpr(instr))
+			continue;
+
+		struct ir3_register *dst = instr->regs[0];
+		if (!(dst->flags & IR3_REG_ARRAY))
+			continue;
+
+		if (dst->array.id != id)
+			continue;
+
+		/*
+		 * At this point, we have narrowed down an instruction
+		 * that writes to the same array.. check if it the write
+		 * is to an array element that we care about:
+		 */
+
+		/* is write to an unknown array element? */
+		if (dst->flags & IR3_REG_RELATIV)
+			return true;
+
+		/* is read from an unknown array element? */
+		if (offset < 0)
+			return true;
+
+		/* is write to same array element? */
+		if (dst->array.offset == offset)
+			return true;
+	}
+
+	return false;
+}
+
+/* Can we fold the mov src into use without invalid flags? */
+static bool
+valid_flags(struct ir3_instruction *use, struct ir3_instruction *mov)
+{
+	struct ir3_register *src = mov->regs[1];
+
+	foreach_src_n (reg, n, use) {
+		if (ssa(reg) != mov)
+			continue;
+
+		if (!ir3_valid_flags(use, n, reg->flags | src->flags))
+			return false;
+	}
+
+	return true;
+}
+
+static bool
+instr_cp_postsched(struct ir3_instruction *mov)
+{
+	struct ir3_register *src = mov->regs[1];
+
+	/* only consider mov's from "arrays", other cases we have
+	 * already considered already:
+	 */
+	if (!(src->flags & IR3_REG_ARRAY))
+		return false;
+
+	int offset = (src->flags & IR3_REG_RELATIV) ? -1 : src->array.offset;
+
+	/* Once we move the array read directly into the consuming
+	 * instruction(s), we will also need to update instructions
+	 * that had a false-dep on the original mov to have deps
+	 * on the consuming instructions:
+	 */
+	struct util_dynarray newdeps;
+	util_dynarray_init(&newdeps, mov->uses);
+
+	foreach_ssa_use (use, mov) {
+		if (use->block != mov->block)
+			continue;
+
+		if (is_meta(use))
+			continue;
+
+		if (has_conflicting_write(mov, use, src->array.id, offset))
+			continue;
+
+		if (conflicts(mov->address, use->address))
+			continue;
+
+		if (!valid_flags(use, mov))
+			continue;
+
+		/* Ok, we've established that it is safe to remove this copy: */
+
+		bool removed = false;
+		foreach_src_n (reg, n, use) {
+			if (ssa(reg) != mov)
+				continue;
+
+			use->regs[n + 1] = ir3_reg_clone(mov->block->shader, src);
+
+			/* preserve (abs)/etc modifiers: */
+			use->regs[n + 1]-> flags |= reg->flags;
+
+			removed = true;
+		}
+
+		/* the use could have been only a false-dep, only add to
+		 * the newdeps array if we've actually updated a real
+		 * src reg for the use:
+		 */
+		if (removed) {
+			util_dynarray_append(&newdeps, struct ir3_instruction *, use);
+
+			/* Remove the use from the src instruction: */
+			_mesa_set_remove_key(mov->uses, use);
+		}
+	}
+
+	/* Once we have the complete set of instruction(s) that are are now
+	 * directly reading from the array, update any false-dep uses to
+	 * now depend on these instructions.  The only remaining uses at
+	 * this point should be false-deps:
+	 */
+	foreach_ssa_use (use, mov) {
+		util_dynarray_foreach(&newdeps, struct ir3_instruction *, instrp) {
+			struct ir3_instruction *newdep = *instrp;
+			ir3_instr_add_dep(use, newdep);
+		}
+	}
+
+	return util_dynarray_num_elements(&newdeps, struct ir3_instruction **) > 0;
+}
+
+bool
+ir3_cp_postsched(struct ir3 *ir)
+{
+	void *mem_ctx = ralloc_context(NULL);
+	bool progress = false;
+
+	ir3_find_ssa_uses(ir, mem_ctx, false);
+
+	foreach_block (block, &ir->block_list) {
+		foreach_instr_safe (instr, &block->instr_list) {
+			if (is_same_type_mov(instr))
+				progress |= instr_cp_postsched(instr);
+		}
+	}
+
+	ralloc_free(mem_ctx);
+
+	return progress;
+}
diff --git a/src/freedreno/ir3/meson.build b/src/freedreno/ir3/meson.build
index 846eccfc443..1bc4ce2f2c6 100644
--- a/src/freedreno/ir3/meson.build
+++ b/src/freedreno/ir3/meson.build
@@ -73,6 +73,7 @@ libfreedreno_ir3_files = files(
   'ir3_context.h',
   'ir3_cf.c',
   'ir3_cp.c',
+  'ir3_cp_postsched.c',
   'ir3_dce.c',
   'ir3_delay.c',
   'ir3_group.c',