Here is the link to the proposed patch :
http://bitbucket.org/basantk/php53perfpatches/raw/ca263ffd272b/safe_address_64bitopt_php53.txt

Richard Smith did the original work and I refined the patch.
In this proposed optimization we can check if the inputs are
sufficiently large enough so that overflow is possible. If overflow is
possible, regular double logic will follow.


Link the the mail sent to internals mailing list :
http://marc.info/?l=php-internals&m=126084384813237&w=2

Microbenchmark testing on Linux x86_64 :
=======================================
Based on the above suggested implementation, I benchmarked 3 implementation of
safe_address on Linux x86_64 (fedora 11) using a micro benchmark. Here are the
results :

--------------------------------------
For a regular nmemb * size + offset when no overflow possible :
nmemb = 23456 size = 67890 offset = 12345
assembly version of safe_address time diff = 26 ticks 
doubles imlementation of safe_address time diff = 72 ticks 
proposed safe_address time diff = 30 ticks 
--------------------------------------

For bigger integer multiplication :

nmemb = 2589934591 size = 4294967295 offset = 5

assembly version of safe_address time diff = 26 ticks 
doubles imlementation of safe_address time diff = 75 ticks 
proposed safe_address time diff = 76 ticks 

--------------------------------------
Here is the micro benchmark link :
http://bitbucket.org/basantk/php53perfpatches/src/tip/safe_address_bench.c

On a ecommerce benchmark on Solaris sparc, new implementation reduced the time spent in _ecalloc to 50%.

Dmitry, any input on this?

I believe this is no longer relevant, as the zend_multiply() code uses __builtin_smulll_overflow() nowadays.