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compiler-constructionllvmcompiler-optimization

Sample program where MOP and MFP are different

I am studying the comparison between Meet over all path(MOP) and Maximum Fixed Point(MFP) in compiler optimizations. Its been said that MFP is a subset of MOP. But I couldn't find out an example in which MFP and MOP are different. Can anyone help me out with any sample program in which MFP and MOP gives different results.

Solution

  • There is such an example in "Monotone Data Flow Analysis Framework" by Kam and Ullman refer this.

    A sample program is 

    if(<some codition>) {
  A = 2;
  B = 3;
}
else {
  A = 3;
  B = 2;
}
C=A+B;

    If we consider the constant propagation analysis of the above program the variable C is a constant in every case. The value will be 5 if the if statement condition evaluates to true or false. But if we perform a fixed point analysis on the above program the C will never be considered as a constant whereas a MOP analysis will provide the information that C is a constant.