merge revision(s) 1f115f141dd17f75049a5e17107906c5bcc372e1: [Backport #19246]

	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]
	---
	 load.c    | 27 +++++++++++++++++++++++----
	 vm.c      |  2 ++
	 vm_core.h |  1 +
	 3 files changed, 26 insertions(+), 4 deletions(-)

1 files changed, 34 insertions, 15 deletions

diff --git a/load.c b/load.c
index 48c7bc4949..ba6f0839af 100644
--- a/load.c
+++ b/load.c
@@ -163,6 +163,12 @@ get_loaded_features_realpaths(rb_vm_t *vm)
 }
 
 static VALUE
+get_loaded_features_realpath_map(rb_vm_t *vm)
+{
+    return vm->loaded_features_realpath_map;
+}
+
+static VALUE
 get_LOADED_FEATURES(ID _x, VALUE *_y)
 {
     return get_loaded_features(GET_VM());
@@ -327,26 +333,34 @@ get_loaded_features_index(rb_vm_t *vm)
 	st_foreach(vm->loaded_features_index, loaded_features_index_clear_i, 0);
 
         VALUE realpaths = vm->loaded_features_realpaths;
+        VALUE realpath_map = vm->loaded_features_realpath_map;
+        VALUE previous_realpath_map = rb_hash_dup(realpath_map);
         rb_hash_clear(realpaths);
-	features = vm->loaded_features;
-	for (i = 0; i < RARRAY_LEN(features); i++) {
-	    VALUE entry, as_str;
-	    as_str = entry = rb_ary_entry(features, i);
-	    StringValue(as_str);
-	    as_str = rb_fstring(rb_str_freeze(as_str));
-	    if (as_str != entry)
-		rb_ary_store(features, i, as_str);
-	    features_index_add(vm, as_str, INT2FIX(i));
-	}
-	reset_loaded_features_snapshot(vm);
+        rb_hash_clear(realpath_map);
+        features = vm->loaded_features;
+        for (i = 0; i < RARRAY_LEN(features); i++) {
+            VALUE entry, as_str;
+            as_str = entry = rb_ary_entry(features, i);
+            StringValue(as_str);
+            as_str = rb_fstring(as_str);
+            if (as_str != entry)
+                rb_ary_store(features, i, as_str);
+            features_index_add(vm, as_str, INT2FIX(i));
+        }
+        reset_loaded_features_snapshot(vm);
 
         features = rb_ary_dup(vm->loaded_features_snapshot);
         long j = RARRAY_LEN(features);
         for (i = 0; i < j; i++) {
             VALUE as_str = rb_ary_entry(features, i);
-            VALUE realpath = rb_check_realpath(Qnil, as_str, NULL);
-            if (NIL_P(realpath)) realpath = as_str;
-            rb_hash_aset(realpaths, rb_fstring(realpath), Qtrue);
+            VALUE realpath = rb_hash_aref(previous_realpath_map, as_str);
+            if (NIL_P(realpath)) {
+                realpath = rb_check_realpath(Qnil, as_str, NULL);
+                if (NIL_P(realpath)) realpath = as_str;
+                realpath = rb_fstring(realpath);
+            }
+            rb_hash_aset(realpaths, realpath, Qtrue);
+            rb_hash_aset(realpath_map, as_str, realpath);
         }
     }
     return vm->loaded_features_index;
@@ -1122,6 +1136,7 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
     volatile VALUE saved_path;
     volatile VALUE realpath = 0;
     VALUE realpaths = get_loaded_features_realpaths(th->vm);
+    VALUE realpath_map = get_loaded_features_realpath_map(th->vm);
     volatile bool reset_ext_config = false;
     struct rb_ext_config prev_ext_config;
 
@@ -1213,7 +1228,9 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
         rb_provide_feature(th2->vm, path);
         VALUE real = realpath;
         if (real) {
-            rb_hash_aset(realpaths, rb_fstring(real), Qtrue);
+            real = rb_fstring(real);
+            rb_hash_aset(realpaths, real, Qtrue);
+            rb_hash_aset(realpath_map, path, real);
         }
     }
     ec->errinfo = saved.errinfo;
@@ -1426,6 +1443,8 @@ Init_load(void)
     vm->loaded_features_index = st_init_numtable();
     vm->loaded_features_realpaths = rb_hash_new();
     rb_obj_hide(vm->loaded_features_realpaths);
+    vm->loaded_features_realpath_map = rb_hash_new();
+    rb_obj_hide(vm->loaded_features_realpath_map);
 
     rb_define_global_function("load", rb_f_load, -1);
     rb_define_global_function("require", rb_f_require, 1);