Chapter 5.8, Problem 5.7PP

Program Plan Intro

Given C code:

void combine5(vec_ptr v, data_t *dest)

{

long i;

long length = vec_length(v);

long limit = length – 1;

data_t *data = get_vec_start(v);

data_t acc = IDENT;

for(i=0; i<limit ; i+=2)

{

acc = (acc OP data[i]) OP data[i+1];

}

for(; i<length ; i++)

{

acc = acc OP data[i];

}

*dest = acc;

}

Memory aliasing:

• It denotes a case where two pointers might designate to memory location that is same.
• The compiler should assume that unlike pointers might be aliased for safe optimizations.
• The program aspects that could limit chances for a compiler in generating optimized code denote optimization blockers.
• If a compiler is unable to determine whether two pointers might be aliased, it should adopt that either case would be possible.
• The possible optimization set is been limited in this case.

Loop unrolling:

• It denotes a program transformation that would reduce count of iterations for a loop.
• It increases count of elements computed in each iteration.
• It reduces number of operations that is not dependent to program directly.
• It reduces count of operations in critical paths of overall computations.