Speed up rebuilding the loaded feature index

Rebuilding the loaded feature index slowed down with the bug fix
for #17885 in 79a4484a072e9769b603e7b4fbdb15b1d7eccb15.  The
slowdown was extreme if realpath emulation was used, but even when
not emulated, it could be about 10x slower.

This adds loaded_features_realpath_map to rb_vm_struct. This is a
hidden hash mapping loaded feature paths to realpaths. When
rebuilding the loaded feature index, look at this hash to get
cached realpath values, and skip calling rb_check_realpath if a
cached value is found.

Fixes [Bug #19246]

1 files changed, 2 insertions, 0 deletions

diff --git a/vm.c b/vm.c
index 27d57a3b24..dfb535d01e 100644
--- a/vm.c
+++ b/vm.c
@@ -2699,6 +2699,7 @@ rb_vm_update_references(void *ptr)
         vm->loaded_features = rb_gc_location(vm->loaded_features);
         vm->loaded_features_snapshot = rb_gc_location(vm->loaded_features_snapshot);
         vm->loaded_features_realpaths = rb_gc_location(vm->loaded_features_realpaths);
+        vm->loaded_features_realpath_map = rb_gc_location(vm->loaded_features_realpath_map);
         vm->top_self = rb_gc_location(vm->top_self);
         vm->orig_progname = rb_gc_location(vm->orig_progname);
 
@@ -2790,6 +2791,7 @@ rb_vm_mark(void *ptr)
         rb_gc_mark_movable(vm->loaded_features);
         rb_gc_mark_movable(vm->loaded_features_snapshot);
         rb_gc_mark_movable(vm->loaded_features_realpaths);
+        rb_gc_mark_movable(vm->loaded_features_realpath_map);
         rb_gc_mark_movable(vm->top_self);
         rb_gc_mark_movable(vm->orig_progname);
         RUBY_MARK_MOVABLE_UNLESS_NULL(vm->coverages);