FUTURE_WORK

The expansion of whole-program analysis should handle, in this order:
	codegen/function_call_index.php
	codegen/oop_method_invocation1.php
	codegen/bench_fibo.php
	3rdparty/shootout/raytrace.php
	TODO: something with includes.

That should cover the vast majority of everything.

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Combine prints:

	print ("str");
	print ("str2");

into 

	print ("strstr2");

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Optimize pow:

pow ($a, 0) => 1
pow ($a, 1) => $a

We can only do the latter is $a is a number.

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Convert print to echo

It does actually make a minor difference
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CONSTANTs defined in the engine can be constant propagated
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Types and === can be converted to false
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Return types of built-in functions (as well as values)
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if ($a == true) can be converted to just if ($a)
Same for
if ($a != false)
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Remove echo ("")
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Pure functions:
strlen
zend_function
md5
sha1
crc32
pi
getrandmax
mt_getrandmax
ord
chr
strtoupper
strtoupper
strcmp
addslashes
htmlspecialchars
htmlentities
dirname
basename
realpath
version_compare
strncmp
strcasecmp
strncasecmp
dechex
hexdec
decbin
decoct
octdec
str_repeat
str_pad
intval
substr
abs
acos
acosh
asin
asinh
atan2
atan
atanh
base_convert
bindec
ceil
cos
cosh
decbin
dechex
decoct
deg2rad
exp
expm1
floor
fmod
getrandmax
hexdec
hypot
is_finite
is_infinite
is_nan
lcg_value
log10
log1p
log
max
min
mt_getrandmax
octdec
pi
pow
rad2deg
round
sin
sinh
sqrt
tan
tanh
ip2long
long2ip
trim
rtrim
ltrim
chop
php_logo_guide
zend_logo_guide
php_edgg_logo_guide

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Functions where we know the return type:
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Functions where we know the return value:
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Fcuntnio which can be optimized, unless the result is false, in which case it may later change:
extension_loaded 
function_exists
class_exists
interface_exists
is_callable
php_version
get_cfg_var
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Unsafe function optimizations performed by APC optimizer:
ini_get
get_magic_quotes_qpc
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Function we probably break:
getlastmod - would be tough to support in a compiler
getmyuid
getmygid
getmyinode
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Function optimizations performed by APC which arent safe ahead-of-time, but are probably safe for APC:
get_current_user
php_sapi_name
php_ini_scanned_files
php_uname
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$x[5] is NULL for non-{string/array}
is this just scalars
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dont forget to lowercase all functions
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printf to echo
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merge constants into printf
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optimize $x[5] for int and $x["str"] for strings
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Zend_call_function:
   we can optimize this a lot. If we control the callee and the caller, then we can call it directly, and, importantly, skip the allocation and deallocation of return values.
   if we control only the caller, we can pass the return value to avoid an allocation and deallocation.
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type-inference everywhere.
 - remove extra array stuff
 - use booleans for conditionals
 - remove unnecessary casts
 - remove concat with ""
 - optimize array access even without constants
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Split every node which has > 1 predecessor.
Optimize
Merge nodes with > 1 predecessor where the predecessors are identical

I think this will see good results for uninitialized variables in particular.
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we could move constants into rvalues. Then we could get the constant zval
without copying it, and just use its result. This would help in heapsort's
gen_random as it just uses them for multiplies.
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Copy-propagation has a few useful places, notably strcat (I measure a 35% improvement).
However, there is a live-range problem, due to SSA. So we need to move the
modification of a variable after its use, if they are independent.
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