Mikroelektronika MIKROE-724 データシート

mikroBasic PRO for dsPIC30/33 and PIC24

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Asm code and SSA optimization

 

If converting code from an earlier version of the compiler, which consists of mixed asm code with the Basic  

 

code, keep in mind that the generated code can substantially differ when SSA optimization option is enabled  

 

or disabled. 

 

This is due to the fact that SSA optimization uses certain working registers to store routine parameters  

 

(W10-W13), rather than storing them onto the function frame.

 

Because of this, user must be very careful when writing asm code as existing values in the working registers  

 

used by SSA optimization can be overwritten. 

 

To avoid this, it is recommended that user includes desired asm code in a separate routine.

Debugging Notes

SSA also influences the code debugging in such a way that the local variables will be available in the Watch Window 

only in those parts of the procedure where they have useful value (eg. on entering the procedure, variable isn’t available 

until its definition). 

Variables can be allocated in one part of the procedure in register W4, and in another part of the procedure in register 

W2, if the optimizer estimates that it is better that way. That means that the local variable has no static address.

Warning Messages Enhancement

Besides the smaller code, SSA also deals with the intensive code analysis, which in turn has the consequence in 

enhancing the warning messages. 

For example, compiler will warn the user that the uninitialized variable is used:

sub procedure SSA_Test()

dim y as char

  if (y) then    ‘ Variable y might not have been initialized

      nop

main:

  SSA_Test()

Related topics: Code Optimization, dsPIC Specifics, mikroBasic PRO for dsPIC30/33 and PIC24 specifics, Memory 

type specifiers