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effiqua asked on

gcc code optimization

I have a C function like below which is part of a file xyz.c and the file is compile using O2 optimization using gcc. The function GetValue() is called almost 200million times  to generate specific data. But for this specific operation cond1 is passed as false, hence code under this condition is never exercise. But, why there is lot of CPU difference in executing GetValue function, when the code chunk 'abc' is commented vs un-commented eventhough the code in that block under (cond1 == true) is not exercised at all.

if the code is commented then GetValue() take - 100 cpu seconds
                     uncomented then GetValue() take  - 120 cpu seconds why ? Is there any problem with GCC optimization ?

inline GetValue(int cond1)

   if (cond1 == true)

      // -- code chunk 'abc'--


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Kent Olsen

8/22/2022 - Mon
Kent Olsen

Hi effiqua,

Is --code chunk-- the only thing in the *if* statement?  If so, the optimization may well be eliminating the test as it's do-nothing code.


The cond1 is determined dynamically. In this case cond1 is passed as false while calling GetValue().
Kent Olsen

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