一、--autoinline, --no_autoinline
These options enable and disable automatic inlining of functions.
The compiler automatically inlines functions at the higher
optimization levels where it is sensible to do so. The -Ospace
and -Otime options, together with some other factors such as
function size, influence how the compiler automatically inlines functions.
Selecting -Otime, in combination with various other factors,
increases the likelihood that functions are inlined.
In general, when automatic inlining is enabled, the compiler inlines
any function that is sensible to inline. When automatic inlining is
disabled, only functions marked as __inline are candidates for inlining.
（如果设置为--no_autoinline，则只有当用户指定__inline关键字，才把
它当做inline函数处理）
Use these options to control the automatic inlining of functions at the
highest optimization levels (-O2 and -O3).
For optimization levels -O0 and -O1, the default is --no_autoinline.
（如果优化级别是O0和O1，则默认是no_autoinline）
For optimization levels -O2 and -O3, the default is --autoinline.
（如果优化级别是O2和O3，则默认是autoinline）