Compilers: Principles and Practice by Pearson

328 Compilers – Principles and Practice

Massalin adopted an approach based on statistical sampling; by carefully selecting the initial

values in the processor registers, the equivalence or otherwise can be determined quickly. He has

given as an example the following code:

signum(int x){

if(x > 0) return 1;

else if(x < 0) return -1;

else return 0;

}

A typical C compiler generates an assembly code of about 8 instructions, with 4 jump instructions.

A good optimizing compiler would generate about 6 instructions with 2 jump instructions. We are

concerned with the jump instructions, because in the modern pipelined processors, with instruction