Yao and Linux

The question "what optimizations gcc performed on different levels?" has been asked time and time again.

We can check this in this way,
$ gcc -c -Q -O3 --help=optimizers > 3.log
$ gcc -c -Q -O2 --help=optimizers > 2.log
$ diff -u 2.log 3.log
--- 2.log    2010-08-20 13:48:57.000000000 +0800
+++ 3.log    2010-08-20 13:48:51.000000000 +0800
@@ -37,7 +37,7 @@
   -ffloat-store                       [disabled]
   -fforward-propagate                 [enabled]
   -fgcse                              [enabled]
-  -fgcse-after-reload                 [disabled]
+  -fgcse-after-reload                 [enabled]
....