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Date: Thu, 24 Jul 2008 19:00:17 +0400
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To: Matt Wilmas <php_lists@realplain.com>
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 Stanislav Malyshev <stas@zend.com>
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Subject: Re: [PHP-DEV] [PATCH] No runtime fetching of built-in global constants
From: dmitry@zend.com (Dmitry Stogov)

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I would propose the attached patch for this optimization.

Opcode caches and encoders will have to disable this optimization with 
ZEND_COMPILE_NO_CONSTANT_SUBSTITUTION

Any objections?

Thanks. Dmitry.

Matt Wilmas wrote:
> Hi Dmitry,
> 
> ----- Original Message -----
> From: "Dmitry Stogov"
> Sent: Thursday, July 24, 2008
> 
>> Hi Matt,
>>
>> Sorry if I missed it.
> 
> No problem. :-)
> 
>> Does this patch make any performance difference?
>>
>> I assume it saves on hash lookup during compilation and its really
>> insignificant time. However it add new scanner rules which may slowdown
>> the whole scanner.
>> For now I don't see a big reason, but may be I didn't see something.
> 
> Yes, I tried to explain the differences in the original message (below).  In
> runtime, FETCH_CONSTANT is saved for the "built-in, global constants"
> (CONST_PERSISTENT).  During compilation, no hash lookup is needed for
> TRUE/FALSE/NULL since they are caught by the scanner, as you saw.  The
> compile-time hash lookups were added when you eliminated runtime fetching
> for TRUE/FALSE/NULL a couple years ago, which has since been looking up the
> other built-in constants too and discarding them, so I just use them. :-)
> Also, right now if the constant isn't found (zend_get_ct_const()), there's
> lowercasing and a second lookup -- only for catching case-insensitive
> TRUE/FALSE/NULL!
> 
> One thing I was wondering about is if this would cause a problem for opcode
> caches if they need to know it's really a "constant constant" and not a
> "literal constant."  If so, can probably have a compiler_options flag to
> disable my compile-time substitution, and the opcode cache can do what it
> wants (substitution with own optimizer, etc.).
> 
>> Do you have any other "postponed" patches?
>> I remember something about string optimizations and long multiply.
> 
> Yeah. :-)  The multiply long one [1] is a pretty small thing that probably
> should be reviewed for a decision (MM's safe_address() function especially),
> though it does speed up mul_function() (* operator) on more platforms.
> 
> The "string changes/optimizations" patch [2] is mostly fine, I think.  Just
> wondering if it's OK to remove the INIT_STRING opcode.  BTW, it has changes
> that make the scanner simpler/smaller if you're concerned about the
> constants patch adding a few rules. ;-D
> 
> [1] http://marc.info/?l=php-internals&m=121630449331340&w=2
> [2] http://marc.info/?l=php-internals&m=121569400218314&w=2
> 
>> Thanks. Dmitry.
>>
> 
> Thanks,
> Matt
> 
> 
>> Matt Wilmas wrote:
>>> Hi all,
>>>
>>> Never heard anything about this optimization after sending it 3 months
> ago
>>> (should've sent a follow-up sooner)...
>>>
>>> Is this something that can be done?  Dmitry?  Details in original
> message.
>>> Patch is unchanged, I just updated them for the current file versions.
>>>
>>> http://realplain.com/php/const_ct_optimization.diff
>>> http://realplain.com/php/const_ct_optimization_5_3.diff
>>>
>>>
>>> Thanks,
>>> Matt
>>>
>>>
>>> ----- Original Message -----
>>> From: "Matt Wilmas"
>>> Sent: Friday, April 18, 2008
>>>
>>>> Hi all,
>>>>
>>>> I changed things so that the many "built-in" constants
> (CONST_PERSISTENT
>>>> ones) will be replaced at compile-time, saving the FETCH_CONSTANT
> opcode,
>>> if
>>>> these changes are usable.  This was added for TRUE/FALSE/NULL 2 years
> ago,
>>>> but seems like it can be done for "lots" of others too.
>>>>
>>>> Since the change 2 years ago, other constants have been getting looked
> up
>>>> also, but just discarded.  And if a constant wasn't found, its name was
>>>> lowercased and looked up again (for case-insensitive TRUE/FALSE/NULL).
>>>> Lowercasing has been removed, since case-insensitive constants can't be
>>> done
>>>> (guess an exception was made for TRUE/FALSE/NULL :-)), and
> TRUE/FALSE/NULL
>>>> get flagged in the scanner (not reserved words, which Marcus did
> briefly a
>>>> few years ago), skipping a hash lookup.  BTW, to get this compile-time
>>>> optimization in a namespace, it needs to be prefixed (::CONSTANT).
>>>>
>>>> I also removed an unnecessary memcmp() in zend_get_constant() -- old
> code
>>>> that was needed a long time ago, it appears.
>>>>
>>>> http://realplain.com/php/const_ct_optimization.diff
>>>> http://realplain.com/php/const_ct_optimization_5_3.diff
>>>>
>>>> Thoughts?
>>>>
>>>>
>>>> Thanks,
>>>> Matt
> 

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Index: Zend/zend_compile.c
===================================================================
RCS file: /repository/ZendEngine2/zend_compile.c,v
retrieving revision 1.647.2.27.2.41.2.74
diff -u -p -d -r1.647.2.27.2.41.2.74 zend_compile.c
--- Zend/zend_compile.c	24 Jul 2008 11:47:49 -0000	1.647.2.27.2.41.2.74
+++ Zend/zend_compile.c	24 Jul 2008 14:40:12 -0000
@@ -3804,6 +3804,12 @@ static zend_constant* zend_get_ct_const(
 	if (c->flags & CONST_CT_SUBST) {
 		return c;
 	}
+	if (!CG(current_namespace) &&
+	    !(CG(compiler_options) & ZEND_COMPILE_NO_CONSTANT_SUBSTITUTION) &&
+	    Z_TYPE(c->value) != IS_CONSTANT &&
+	    Z_TYPE(c->value) != IS_CONSTANT_ARRAY) {
+		return c;
+	}
 	return NULL;
 }
 /* }}} */
@@ -5169,12 +5175,14 @@ void zend_do_use(znode *ns_name, znode *
 void zend_do_declare_constant(znode *name, znode *value TSRMLS_DC) /* {{{ */
 {
 	zend_op *opline;
+	zend_constant *c;
 
 	if(Z_TYPE(value->u.constant) == IS_CONSTANT_ARRAY) {
 		zend_error(E_COMPILE_ERROR, "Arrays are not allowed as constants");
 	}
 
-	if (zend_get_ct_const(&name->u.constant TSRMLS_CC)) {
+	c = zend_get_ct_const(&name->u.constant TSRMLS_CC);
+	if (c && (c->flags & CONST_CT_SUBST)) {
 		zend_error(E_COMPILE_ERROR, "Cannot redeclare constant '%s'", Z_STRVAL(name->u.constant));
 	}
 
Index: Zend/zend_compile.h
===================================================================
RCS file: /repository/ZendEngine2/zend_compile.h,v
retrieving revision 1.316.2.8.2.12.2.27
diff -u -p -d -r1.316.2.8.2.12.2.27 zend_compile.h
--- Zend/zend_compile.h	24 Jul 2008 11:47:49 -0000	1.316.2.8.2.12.2.27
+++ Zend/zend_compile.h	24 Jul 2008 14:40:13 -0000
@@ -762,6 +762,9 @@ END_EXTERN_C()
 /* generate ZEND_DECLARE_INHERITED_CLASS_DELAYED opcode to delay early binding */
 #define ZEND_COMPILE_DELAYED_BINDING			(1<<4)
 
+/* disable constant substitution at compile-time */
+#define ZEND_COMPILE_NO_CONSTANT_SUBSTITUTION	(1<<5)
+
 /* The default value for CG(compiler_options) */
 #define ZEND_COMPILE_DEFAULT					ZEND_COMPILE_HANDLE_OP_ARRAY
 

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