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, 1 insertions, 0 deletions

diff --git a/vm_core.h b/vm_core.h
index 74824f48c6..c68cfaf984 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -676,6 +676,7 @@ typedef struct rb_vm_struct {
     VALUE loaded_features;
     VALUE loaded_features_snapshot;
     VALUE loaded_features_realpaths;
+    VALUE loaded_features_realpath_map;
     struct st_table *loaded_features_index;
     struct st_table *loading_table;
 #if EXTSTATIC