Bug #252: Array#sort doesn't respect overridden <=>

I guess I should ask: bug, feature, or undefined behavior?

On Jul 9, 2008, at 6:00 PM, Ryan Davis wrote:

> junk = %w[these words should be sorted in the order of their length]
> puts junk.sort
>
> MRI (1.8, 1.9) does not respect new behavior of <=>.
>
> Bug or feature?


I seem to remember this from a while back--I seem to remember that   
String is special-cased for performance.

On Jul 9, 2008, at 17:27 , Dave Thomas wrote:

>
> On Jul 9, 2008, at 6:00 PM, Ryan Davis wrote:
>
>> junk = %w[these words should be sorted in the order of their length]
>> puts junk.sort
>>
>> MRI (1.8, 1.9) does not respect new behavior of <=>.
>>
>> Bug or feature?
>
>
> I seem to remember this from a while back--I seem to remember that   
> String is special-cased for performance.

and that's cool... but I'd like an "official" weigh in describing it  
as either specification or implementation detail. ATM, I don't think  
rubinius would see a performance loss if it respected the overridden  
<=> method.

This seems to be a common performance trick in MRI, esp. for Fixnums and Strings.

Looking at array.c (sort_2), indeed Fixnums and Strings are special-cased.

I also checked JRuby, and JRuby follows what MRI does (and this does improve performance for Fixnum and String arrays).

Hi,

At Thu, 10 Jul 2008 16:44:33 +0900,
Vladimir Sizikov wrote in [ruby-core:17720]:
> This seems to be a common performance trick in MRI, esp. for Fixnums and Strings.
> 
> Looking at array.c (sort_2), indeed Fixnums and Strings are special-cased.

I've forgotten to post this patch.


Index: intern.h
===================================================================
--- intern.h	(revision 18354)
+++ intern.h	(working copy)
@@ -168,4 +168,5 @@ void rb_alias _((VALUE, ID, ID));
 void rb_attr _((VALUE,ID,int,int,int));
 int rb_method_boundp _((VALUE, ID, int));
+int rb_method_basic_definition_p _((VALUE, ID));
 VALUE rb_dvar_defined _((ID));
 VALUE rb_dvar_curr _((ID));
Index: array.c
===================================================================
--- array.c	(revision 18354)
+++ array.c	(working copy)
@@ -1686,6 +1686,24 @@ struct ary_sort_data {
     VALUE *ptr;
     long len;
+    int opt_methods;
+    int opt_inited;
 };

+enum {
+    sort_opt_Fixnum,
+    sort_opt_String,
+    sort_optimizable_count
+};
+
+#define STRING_P(s) (TYPE(s) == T_STRING && CLASS_OF(s) == rb_cString)
+
+#define SORT_OPTIMIZABLE_BIT(type) (1U << TOKEN_PASTE(sort_opt_,type))
+#define SORT_OPTIMIZABLE(data, type) \
+    ((data->opt_inited & SORT_OPTIMIZABLE_BIT(type)) ? \
+     (data->opt_methods & SORT_OPTIMIZABLE_BIT(type)) : \
+     ((data->opt_inited |= SORT_OPTIMIZABLE_BIT(type)), \
+      rb_method_basic_definition_p(TOKEN_PASTE(rb_c,type), id_cmp) && \
+      (data->opt_methods |= SORT_OPTIMIZABLE_BIT(type))))
+
 static void
 ary_sort_check(data)
@@ -1719,11 +1737,11 @@ sort_2(ap, bp, data)
     int n;

-    if (FIXNUM_P(a) && FIXNUM_P(b)) {
+    if (FIXNUM_P(a) && FIXNUM_P(b) && SORT_OPTIMIZABLE(data, Fixnum)) {
 	if ((long)a > (long)b) return 1;
 	if ((long)a < (long)b) return -1;
 	return 0;
     }
-    if (TYPE(a) == T_STRING) {
-	if (TYPE(b) == T_STRING) return rb_str_cmp(a, b);
+    if (STRING_P(a) && STRING_P(b) && SORT_OPTIMIZABLE(data, String)) {
+	return rb_str_cmp(a, b);
     }

@@ -1743,4 +1761,6 @@ sort_internal(ary)
     data.ary = ary;
     data.ptr = RARRAY(ary)->ptr; data.len = RARRAY(ary)->len;
+    data.opt_methods = 0;
+    data.opt_inited = 0;
     qsort(RARRAY(ary)->ptr, RARRAY(ary)->len, sizeof(VALUE),
 	  rb_block_given_p()?sort_1:sort_2, &data);
Index: eval.c
===================================================================
--- eval.c	(revision 18355)
+++ eval.c	(working copy)
@@ -405,6 +405,7 @@ static ID __id__, __send__, respond_to;

 #define NOEX_TAINTED 8
-#define NOEX_SAFE(n) ((n) >> 4)
-#define NOEX_WITH(n, v) ((n) | (v) << 4)
+#define NOEX_BASIC 16
+#define NOEX_SAFE(n) ((n) >> 5)
+#define NOEX_WITH(n, v) ((n) | (v) << 5 | (ruby_running ? 0 : NOEX_BASIC))
 #define NOEX_WITH_SAFE(n) NOEX_WITH(n, ruby_safe_level)

@@ -4218,5 +4219,14 @@ module_setup(module, n)
 }

-static NODE *basic_respond_to = 0;
+int
+rb_method_basic_definition_p(klass, id)
+    VALUE klass;
+    ID id;
+{
+    NODE *node = rb_method_node(klass, id);
+    if (node && (node->nd_noex & NOEX_BASIC))
+	return 1;
+    return 0;
+}

 int
@@ -4228,5 +4238,5 @@ rb_obj_respond_to(obj, id, priv)
     VALUE klass = CLASS_OF(obj);

-    if (rb_method_node(klass, respond_to) == basic_respond_to) {
+    if (rb_method_basic_definition_p(klass, respond_to)) {
 	return rb_method_boundp(klass, id, !priv);
     }
@@ -8185,6 +8195,4 @@ Init_eval()
     rb_define_method(rb_mKernel, "respond_to?", obj_respond_to, -1);
     respond_to   = rb_intern("respond_to?");
-    rb_global_variable((void *)&basic_respond_to);
-    basic_respond_to = rb_method_node(rb_cObject, respond_to);

     rb_define_global_function("raise", rb_f_raise, -1);

Index: include/ruby/intern.h
===================================================================
--- include/ruby/intern.h	(revision 18354)
+++ include/ruby/intern.h	(working copy)
@@ -250,4 +250,5 @@ void rb_alias(VALUE, ID, ID);
 void rb_attr(VALUE,ID,int,int,int);
 int rb_method_boundp(VALUE, ID, int);
+int rb_method_basic_definition_p(VALUE, ID);
 VALUE rb_eval_cmd(VALUE, VALUE, int);
 int rb_obj_respond_to(VALUE, ID, int);
Index: include/ruby/node.h
===================================================================
--- include/ruby/node.h	(revision 18354)
+++ include/ruby/node.h	(working copy)
@@ -464,5 +464,6 @@ typedef struct RNode {
 #define NOEX_PRIVATE   0x02
 #define NOEX_PROTECTED 0x04
-#define NOEX_MASK      0x06 /* 1110 */
+#define NOEX_MASK      0x06 /* 0110 */
+#define NOEX_BASIC     0x08

 #define NOEX_UNDEF     NOEX_NOSUPER
@@ -473,5 +474,5 @@ typedef struct RNode {

 #define NOEX_SAFE(n) (((n) >> 8) & 0x0F)
-#define NOEX_WITH(n, s) ((s << 8) | n)
+#define NOEX_WITH(n, s) ((s << 8) | (n) | (ruby_running ? 0 : NOEX_BASIC))
 #define NOEX_WITH_SAFE(n) NOEX_WITH(n, rb_safe_level())

Index: array.c
===================================================================
--- array.c	(revision 18354)
+++ array.c	(working copy)
@@ -1447,8 +1447,30 @@ rb_ary_reverse_m(VALUE ary)
 }

+struct ary_sort_data {
+    VALUE ary;
+    int opt_methods;
+    int opt_inited;
+};
+
+enum {
+    sort_opt_Fixnum,
+    sort_opt_String,
+    sort_optimizable_count
+};
+
+#define STRING_P(s) (TYPE(s) == T_STRING && CLASS_OF(s) == rb_cString)
+
+#define SORT_OPTIMIZABLE_BIT(type) (1U << TOKEN_PASTE(sort_opt_,type))
+#define SORT_OPTIMIZABLE(data, type) \
+    ((data->opt_inited & SORT_OPTIMIZABLE_BIT(type)) ? \
+     (data->opt_methods & SORT_OPTIMIZABLE_BIT(type)) : \
+     ((data->opt_inited |= SORT_OPTIMIZABLE_BIT(type)), \
+      rb_method_basic_definition_p(TOKEN_PASTE(rb_c,type), id_cmp) && \
+      (data->opt_methods |= SORT_OPTIMIZABLE_BIT(type))))
+
 static VALUE
-sort_reentered(VALUE *klass)
+sort_reentered(VALUE ary)
 {
-    if (*klass) {
+    if (RBASIC(ary)->klass) {
 	rb_raise(rb_eRuntimeError, "sort reentered");
     }
@@ -1459,5 +1481,6 @@ static int
 sort_1(const void *ap, const void *bp, void *dummy)
 {
-    VALUE retval = sort_reentered(dummy);
+    struct ary_sort_data *data = dummy;
+    VALUE retval = sort_reentered(data->ary);
     VALUE a = *(const VALUE *)ap, b = *(const VALUE *)bp;
     int n;
@@ -1465,5 +1488,5 @@ sort_1(const void *ap, const void *bp, v
     retval = rb_yield_values(2, a, b);
     n = rb_cmpint(retval, a, b);
-    sort_reentered(dummy);
+    sort_reentered(data->ary);
     return n;
 }
@@ -1472,20 +1495,21 @@ static int
 sort_2(const void *ap, const void *bp, void *dummy)
 {
-    VALUE retval = sort_reentered(dummy);
+    struct ary_sort_data *data = dummy;
+    VALUE retval = sort_reentered(data->ary);
     VALUE a = *(const VALUE *)ap, b = *(const VALUE *)bp;
     int n;

-    if (FIXNUM_P(a) && FIXNUM_P(b)) {
+    if (FIXNUM_P(a) && FIXNUM_P(b) && SORT_OPTIMIZABLE(data, Fixnum)) {
 	if ((long)a > (long)b) return 1;
 	if ((long)a < (long)b) return -1;
 	return 0;
     }
-    if (TYPE(a) == T_STRING) {
-	if (TYPE(b) == T_STRING) return rb_str_cmp(a, b);
+    if (STRING_P(a) && STRING_P(b) && SORT_OPTIMIZABLE(data, String)) {
+	return rb_str_cmp(a, b);
     }

     retval = rb_funcall(a, id_cmp, 1, b);
     n = rb_cmpint(retval, a, b);
-    sort_reentered(dummy);
+    sort_reentered(data->ary);

     return n;
@@ -1514,8 +1538,12 @@ rb_ary_sort_bang(VALUE ary)
     if (RARRAY_LEN(ary) > 1) {
 	VALUE tmp = ary_make_shared(ary);
+	struct ary_sort_data data;

 	RBASIC(tmp)->klass = 0;
+	data.ary = tmp;
+	data.opt_methods = 0;
+	data.opt_inited = 0;
 	ruby_qsort(RARRAY_PTR(tmp), RARRAY_LEN(tmp), sizeof(VALUE),
-		   rb_block_given_p()?sort_1:sort_2, &RBASIC(tmp)->klass);
+		   rb_block_given_p()?sort_1:sort_2, &data);
 	if (RARRAY(ary)->ptr != RARRAY(tmp)->ptr) {
 	    if (!ARY_SHARED_P(ary)) xfree(RARRAY(ary)->ptr);
Index: vm_method.c
===================================================================
--- vm_method.c	(revision 18354)
+++ vm_method.c	(working copy)
@@ -1045,4 +1045,13 @@ rb_mod_modfunc(int argc, VALUE *argv, VA
 }

+int
+rb_method_basic_definition_p(VALUE klass, ID id)
+{
+    NODE *node = rb_method_node(klass, id);
+    if (node && (node->nd_noex & NOEX_BASIC))
+	return 1;
+    return 0;
+}
+
 /*
  *  call-seq:
@@ -1054,6 +1063,4 @@ rb_mod_modfunc(int argc, VALUE *argv, VA
  */

-static NODE *basic_respond_to = 0;
-
 int
 rb_obj_respond_to(VALUE obj, ID id, int priv)
@@ -1061,5 +1068,5 @@ rb_obj_respond_to(VALUE obj, ID id, int 
     VALUE klass = CLASS_OF(obj);

-    if (rb_method_node(klass, idRespond_to) == basic_respond_to) {
+    if (rb_method_basic_definition_p(klass, idRespond_to)) {
 	return rb_method_boundp(klass, id, !priv);
     }
@@ -1109,6 +1116,4 @@ Init_eval_method(void)

     rb_define_method(rb_mKernel, "respond_to?", obj_respond_to, -1);
-    basic_respond_to = rb_method_node(rb_cObject, idRespond_to);
-    rb_register_mark_object((VALUE)basic_respond_to);

     rb_define_private_method(rb_cModule, "remove_method", rb_mod_remove_method, -1);


-- 
Nobu Nakada

Hi,

In message "Re: [ruby-core:18114] Re: [Ruby 1.8 - Bug #252] Array#sort doesn't respect overridden <=>"
    on Mon, 4 Aug 2008 15:44:50 +0900, Nobuyoshi Nakada <[e-mail]> writes:

|I've forgotten to post this patch.

Interesting.  Could you apply the patch (to trunk)?

							matz.

Hi,

In message "Re: [ruby-core:18177] Re: [Ruby 1.8 - Bug #252] Array#sort doesn't respect overridden <=>"
    on Fri, 8 Aug 2008 06:17:41 +0900, Lin Jen-Shin <[e-mail]> writes:

|And should this behavior apply to condition (e.g. if, unless, while, etc.)
|to call :nil? as well?

No.

							matz.

Hi,

In message "Re: [ruby-core:18124] Re: [Ruby 1.8 - Bug #252] Array#sort doesn't respect overridden <=>"
    on Tue, 5 Aug 2008 04:49:27 +0900, Charles Oliver Nutter <[e-mail]> writes:

|So this is going to be a behavioral change now? My reading of the patch 
|tells me it's now checking to see if <=> has been overridden and if so 
|using the path that actually calls it. As Ryan pointed out, this would 
|be new behavior. Can we get an official ruling on what is correct in 1.8 
|and 1.9.x?

We are not going to change 1.8 semantic in the near future.  We should
keep compatibility, even when it's inconsistent, as long as it's not
"wrong".

For 1.9, I think it's better to adopt the new behavior.  What do you
think?

							matz.

If this patch was applied, we should close the bug.

• Status changed from Open to Closed

patch already applied.