freedreno/ir3: clean up dangling false-dep's

Maybe there is a better way for this..  where it comes useful is "array"
loads, which end up as a false-dep for a later array store.

If all the uses of an array load are CP'd into their consumer, it still
leaves the dangling array load, leading to funny things like:

  mov.u32u32 r5.y, r0.y
  mov.u32u32 r5.y, r0.z

Signed-off-by: Rob Clark <robdclark@gmail.com>

src/gallium/drivers/freedreno/ir3/ir3.h

@@ -360,6 +360,8 @@ struct ir3_instruction {
 	/* Entry in ir3_block's instruction list: */
 	struct list_head node;
 
+	int use_count;      /* currently just updated/used by cp */
+
 #ifdef DEBUG
 	uint32_t serialno;
 #endif

src/gallium/drivers/freedreno/ir3/ir3_cp.c

@@ -309,6 +309,26 @@ lower_immed(struct ir3_cp_ctx *ctx, struct ir3_register *reg, unsigned new_flags
 	return reg;
 }
 
+static void
+unuse(struct ir3_instruction *instr)
+{
+	debug_assert(instr->use_count > 0);
+
+	if (--instr->use_count == 0) {
+		struct ir3_block *block = instr->block;
+
+		instr->barrier_class = 0;
+		instr->barrier_conflict = 0;
+
+		/* we don't want to remove anything in keeps (which could
+		 * be things like array store's)
+		 */
+		for (unsigned i = 0; i < block->keeps_count; i++) {
+			debug_assert(block->keeps[i] != instr);
+		}
+	}
+}
+
 /**
  * Handle cp for a given src register.  This additionally handles
  * the cases of collapsing immedate/const (which replace the src
@@ -339,6 +359,8 @@ reg_cp(struct ir3_cp_ctx *ctx, struct ir3_instruction *instr,
 
 			instr->barrier_class |= src->barrier_class;
 			instr->barrier_conflict |= src->barrier_conflict;
+
+			unuse(src);
 		}
 
 	} else if (is_same_type_mov(src) &&
@@ -558,6 +580,7 @@ instr_cp(struct ir3_cp_ctx *ctx, struct ir3_instruction *instr)
 			instr->regs[2] = cond->regs[2];
 			instr->barrier_class |= cond->barrier_class;
 			instr->barrier_conflict |= cond->barrier_conflict;
+			unuse(cond);
 			break;
 		default:
 			break;
@@ -573,6 +596,27 @@ ir3_cp(struct ir3 *ir, struct ir3_shader_variant *so)
 			.so = so,
 	};
 
+	/* This is a bit annoying, and probably wouldn't be necessary if we
+	 * tracked a reverse link from producing instruction to consumer.
+	 * But we need to know when we've eliminated the last consumer of
+	 * a mov, so we need to do a pass to first count consumers of a
+	 * mov.
+	 */
+	list_for_each_entry (struct ir3_block, block, &ir->block_list, node) {
+		list_for_each_entry (struct ir3_instruction, instr, &block->instr_list, node) {
+			struct ir3_instruction *src;
+
+			/* by the way, we don't acount for false-dep's, so the CP
+			 * pass should always happen before false-dep's are inserted
+			 */
+			debug_assert(instr->deps_count == 0);
+
+			foreach_ssa_src(src, instr) {
+				src->use_count++;
+			}
+		}
+	}
+
 	ir3_clear_mark(ir);
 
 	for (unsigned i = 0; i < ir->noutputs; i++) {