optimize
#pragma optimize( "[optimization-list]", {on | off} )
Feature Only in Professional and Enterprise Edition Code optimization is supported only in Visual C++ Professional and Enterprise Editions. For more information, see Visual C++ Editions.
Specifies optimizations to be performed on a function-by-function basis. The optimize pragma must appear outside a function and takes effect at the first function defined after the pragma is seen. The on and off arguments turn options specified in the optimization-list on or off.
The optimization-list can be zero or more of the parameters shown in Table 2.2.
Table 2.2 Parameters of the optimize Pragma
Parameter(s) Type of optimization
a Assume no aliasing.
g Enable global optimizations.
p Improve floating-point consistency.
s or t Specify short or fast sequences of machine code.
w Assume no aliasing across function calls.
y Generate frame pointers on the program stack.
These are the same letters used with the /O compiler options. For example,
#pragma optimize( "atp", on )
Using the optimize pragma with the empty string (" ") is a special form of the directive. It either turns off all optimizations or restores them to their original (or default) settings.
#pragma optimize( "", off )
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#pragma optimize( "", on )
原文：https://www.cnblogs.com/kuangke/p/9525054.html