Don't attempt to cache glyph metrics for FONT_INVALID_CODE

This was causing massive slowdown in redisplay when eg #xfe0f
(VARIATION SELECTOR-16) was present, as the cache ended up very large,
unused, and being recreated on every call to font_fill_lglyph_metrics
(Bug#39133).

* src/composite.c (fill_gstring_body): Hoist FONT_OBJECT_P check out
of loop.  Calculate glyph code and check for FONT_INVALID_CODE before
calling font_fill_lglyph_metrics.  Pass glyph code to it.

* src/font.c (font_fill_lglyph_metrics): Add code parameter, move
glyph code calculation up the call stack into fill_gstring_body.

* src/font.h: Adjust font_fill_lglyph_metrics prototype.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/font.h b/src/font.h
index 633d92709c5..6f4792afe55 100644
--- a/src/font.h
+++ b/src/font.h
@@ -886,7 +886,7 @@ extern Lisp_Object font_update_drivers (struct frame *f, Lisp_Object list);
 extern Lisp_Object font_range (ptrdiff_t, ptrdiff_t, ptrdiff_t *,
                                struct window *, struct face *,
                                Lisp_Object);
-extern void font_fill_lglyph_metrics (Lisp_Object, Lisp_Object);
+extern void font_fill_lglyph_metrics (Lisp_Object, struct font *, unsigned int);
 
 extern Lisp_Object font_put_extra (Lisp_Object font, Lisp_Object prop,
                                    Lisp_Object val);