Do not invoke clear check on respawn.

grid.c

@@ -60,21 +60,6 @@ static const struct grid_cell_entry grid_cleared_entry = {
 };
 
 #ifdef __APPLE__
-static void
-grid_check_lines(struct grid *gd)
-{
-	u_int	i, j;
-
-	for (i = 0; i < gd->hsize + gd->sy; i++) {
-		for (j = i + 1; j < gd->hsize + gd->sy; j++) {
-			if (gd->linedata[i].celldata != NULL)
-				assert(gd->linedata[i].celldata != gd->linedata[j].celldata);
-			if (gd->linedata[i].extddata != NULL)
-				assert(gd->linedata[i].extddata != gd->linedata[j].extddata);
-		}
-	}
-}
-
 void
 grid_check_is_clear(struct grid *gd)
 {
@@ -104,11 +89,6 @@ grid_check_is_clear(struct grid *gd)
 	}
 }
 #else
-static void
-grid_check_lines(__unused struct grid *gd)
-{
-}
-
 void
 grid_check_is_clear(__unused struct grid *gd)
 {
@@ -506,8 +486,6 @@ grid_scroll_history(struct grid *gd, u_int bg)
 	gd->linedata[gd->hsize].time = current_time;
 	gd->hsize++;
 	gd->scroll_added++;
-
-	grid_check_lines(gd);
 }
 
 /* Clear the history. */
@@ -557,8 +535,6 @@ grid_scroll_history_region(struct grid *gd, u_int upper, u_int lower, u_int bg)
 	gd->hscrolled++;
 	gd->hsize++;
 	gd->scroll_added++;
-
-	grid_check_lines(gd);
 }
 
 /* Expand line to fit to cell. */
@@ -820,8 +796,6 @@ grid_move_lines(struct grid *gd, u_int dy, u_int py, u_int ny, u_int bg)
 	}
 	if (py != 0 && (py < dy || py >= dy + ny))
 		gd->linedata[py - 1].flags &= ~GRID_LINE_WRAPPED;
-
-	grid_check_lines(gd);
 }
 
 /* Move a group of cells. */
@@ -1311,8 +1285,6 @@ grid_duplicate_lines(struct grid *dst, u_int dy, struct grid *src, u_int sy,
 		sy++;
 		dy++;
 	}
-
-	grid_check_lines(dst);
 }
 
 /* Mark line as dead. */
@@ -1609,8 +1581,6 @@ grid_reflow(struct grid *gd, u_int sx)
 	gd->linedata = target->linedata;
 	free(target);
 	gd->scroll_generation++;
-
-	grid_check_lines(gd);
 }
 
 /* Convert to position based on wrapped lines. */

screen.c

@@ -99,12 +99,12 @@ screen_init(struct screen *s, u_int sx, u_int sy, u_int hlimit)
 	s->write_list = NULL;
 	s->hyperlinks = NULL;
 
-	screen_reinit(s);
+	screen_reinit(s, 1);
 }
 
 /* Reinitialise screen. */
 void
-screen_reinit(struct screen *s)
+screen_reinit(struct screen *s, int check)
 {
 	s->cx = 0;
 	s->cy = 0;
@@ -123,7 +123,8 @@ screen_reinit(struct screen *s)
 	s->saved_cy = UINT_MAX;
 
 	screen_reset_tabs(s);
-	grid_check_is_clear(s->grid);
+	if (check)
+		grid_check_is_clear(s->grid);
 	grid_clear_lines(s->grid, s->grid->hsize, s->grid->sy, 8);
 
 	screen_clear_selection(s);

spawn.c

@@ -273,7 +273,7 @@ spawn_pane(struct spawn_context *sc, char **cause)
 			sc->wp0->fd = -1;
 		}
 		window_pane_reset_mode_all(sc->wp0);
-		screen_reinit(&sc->wp0->base);
+		screen_reinit(&sc->wp0->base, 0);
 		if (sc->wp0->ictx != NULL) {
 			input_free(sc->wp0->ictx);
 			sc->wp0->ictx = NULL;

tmux.h

@@ -3502,7 +3502,7 @@ int	 redraw_get_status_border_cell_type(struct redraw_span **, u_int);
 
 /* screen.c */
 void	 screen_init(struct screen *, u_int, u_int, u_int);
-void	 screen_reinit(struct screen *);
+void	 screen_reinit(struct screen *, int);
 void	 screen_free(struct screen *);
 void	 screen_reset_tabs(struct screen *);
 void	 screen_reset_hyperlinks(struct screen *);