ipa_rescopes_globals

Rescopes the application global variables, that are only used in one function, to local static. The change to static enables other optimizations that improve alias analysis and load/store optimizations.

  #pragma ipa_rescopes_globals on | off | reset

  

Ensure that the following requirements are met to rescope the application global variables to local static:

• Program IPA is enabled in all application source files.
• Use of #pragma ipa_rescopes_globals on in all application source files (prefix file or with -flag ipa_rescopes_globals on the commandline).
• main() is defined in one of the application files.
• It is not necessary, or even desirable, to have standard library, runtime or startup code compiled with program IPA and ipa_rescopes_globals on.

However, it is important to have as many of your application sources as possible compiled with those options enabled.

For a simple example, compile/assemble your startup code without program IPA. Compile all of the application code with program IPA, #pragma ipa_rescopes_globals on and link the startup objects, your application objects and the library archives. For more details on Program IPA linking procedures, refer Interprocedural Analysis.

For a complex example where the application sources are put into groups, compiled and then pre-built into several archives or partially linked objects and the build procedure cannot be matched with the simple example, following changes to the build procedure are suggested:

• Try to make the build setup as similar to the simple example as possible. This will help you identify if the code will benefit from ipa_rescopes_globals or you will need to modify your source files to get a successful link. For more details, refer Generating a successful link.
• All of your functions are not visible to the compiler at once during program IPA. It is possible that a defined global variable in your core files may be used by only one core file but might also be used in one of your application archives that you were unable to build the simple way. If this is true, ipa_rescopes_globals will rescope the variable and at link time, your application archive will not be able to find the variable and you will get an undefined symbol link error.
  Note: If you get a successful link you do not have to make any further changes to the build or source.

Optimization prevents an improper build. If you do not get a successful link or you only get a few such link errors, identify the source file that defines the "undefined" symbol and try one of the following (in decreasing order of general preference):

• Move the definition of the symbol into the application archive. Symbols that are undefined do not get rescoped.
• Force the export of the symbol with __declspec(force_export). Symbols that are exported do not get rescoped.
• Change the symbols to weak with __declspec(weak) by inserting before definition. Weak symbols do not get rescoped.
• Change the symbols to volatile. Volatile symbols do not get rescoped. with smaller, more efficient groups of instructions.