ir3/sched: Handle branch condition in split_pred()

Before this, if there was a block with multiple things writing p0.x,
it was a tossup whether the right one would be used as the branch
condition. Found by inspection.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6752>

src/freedreno/ir3/ir3_sched.c

@@ -944,6 +944,16 @@ split_pred(struct ir3_sched_ctx *ctx)
 		}
 	}
 
+	if (ctx->block->condition == ctx->pred) {
+		if (!new_pred) {
+			new_pred = split_instr(ctx, ctx->pred);
+			/* original pred is scheduled, but new one isn't: */
+			new_pred->flags &= ~IR3_INSTR_MARK;
+		}
+		ctx->block->condition = new_pred;
+		d("new branch condition");
+	}
+
 	/* all remaining predicated remapped to new pred: */
 	ctx->pred = NULL;