Issue #8142 has been reported by tmm1 (Aman Gupta).

----------------------------------------
Bug #8142: [patch] iseq: reduce array allocations for simple sequences
https://bugs.ruby-lang.org/issues/8142

Author: tmm1 (Aman Gupta)
Status: Open
Priority: Normal
Assignee: ko1 (Koichi Sasada)
Category: 
Target version: 
ruby -v: ruby 2.1.0dev (2013-03-20 trunk 39832) [x86_64-darwin12.2.1]


Allocate iseq->mark_ary on demand, only if needed.

In my application, this reduces long lived arrays on the heap significantly.

:T_ARRAY=>88166 # before
:T_ARRAY=>62932 # after

diff --git a/compile.c b/compile.c
index 9360f5b..aafae05 100644
--- a/compile.c
+++ b/compile.c
@@ -416,7 +416,7 @@ static int
 iseq_add_mark_object(rb_iseq_t *iseq, VALUE v)
 {
     if (!SPECIAL_CONST_P(v)) {
-	rb_ary_push(iseq->mark_ary, v);
+	rb_iseq_add_mark_object(iseq, v);
     }
     return COMPILE_OK;
 }
diff --git a/insns.def b/insns.def
index 979aa1c..bb9fc3f 100644
--- a/insns.def
+++ b/insns.def
@@ -1237,7 +1237,7 @@ setinlinecache
 (VALUE val)
 {
     if (ic->ic_value.value == Qundef) {
-	rb_ary_push(GET_ISEQ()->mark_ary, val);
+	rb_iseq_add_mark_object(GET_ISEQ(), val);
     }
     ic->ic_value.value = val;
     ic->ic_vmstat = GET_VM_STATE_VERSION() - ruby_vm_const_missing_count;
diff --git a/iseq.c b/iseq.c
index 288d3bf..eab237a 100644
--- a/iseq.c
+++ b/iseq.c
@@ -237,6 +237,17 @@ set_relation(rb_iseq_t *iseq, const VALUE parent)
     }
 }
 
+void
+rb_iseq_add_mark_object(rb_iseq_t *iseq, VALUE obj)
+{
+    if (!RTEST(iseq->mark_ary)) {
+        iseq->mark_ary = rb_ary_tmp_new(3);
+        OBJ_UNTRUST(iseq->mark_ary);
+        RBASIC(iseq->mark_ary)->klass = 0;
+    }
+    rb_ary_push(iseq->mark_ary, obj);
+}
+
 static VALUE
 prepare_iseq_build(rb_iseq_t *iseq,
 		   VALUE name, VALUE path, VALUE absolute_path, VALUE first_lineno,
@@ -259,9 +270,7 @@ prepare_iseq_build(rb_iseq_t *iseq,
     }
 
     iseq->defined_method_id = 0;
-    iseq->mark_ary = rb_ary_tmp_new(3);
-    OBJ_UNTRUST(iseq->mark_ary);
-    RBASIC(iseq->mark_ary)->klass = 0;
+    iseq->mark_ary = 0;
 
 
     /*
@@ -2060,8 +2069,7 @@ rb_iseq_build_for_ruby2cext(
     iseq->location.label = rb_str_new2(name);
     iseq->location.path = rb_str_new2(path);
     iseq->location.first_lineno = first_lineno;
-    iseq->mark_ary = rb_ary_tmp_new(3);
-    OBJ_UNTRUST(iseq->mark_ary);
+    iseq->mark_ary = 0;
     iseq->self = iseqval;
 
     iseq->iseq = ALLOC_N(VALUE, iseq->iseq_size);
diff --git a/iseq.h b/iseq.h
index 0790529..4de0816 100644
--- a/iseq.h
+++ b/iseq.h
@@ -23,6 +23,7 @@ VALUE rb_iseq_build_from_ary(rb_iseq_t *iseq, VALUE locals, VALUE args,
 			     VALUE exception, VALUE body);
 
 /* iseq.c */
+void rb_iseq_add_mark_object(rb_iseq_t *iseq, VALUE obj);
 VALUE rb_iseq_load(VALUE data, VALUE parent, VALUE opt);
 VALUE rb_iseq_parameters(const rb_iseq_t *iseq, int is_proc);
 struct st_table *ruby_insn_make_insn_table(void);



-- 
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