Peractice Problem $54$

At times, GCC does its own version of converting array code to pointer code.

For example, with integer data and addition as the combining operation, it

generates the following code for the inner loop of a variant of combine $5$ that

uses eight$-$way loop unrolling:

$.$L$6$:

addl $(8$eax

addl $4($seax$),$ sedx

addl $8($seax$),$ sedx

addl $12($seax$),$ sedx

addl $16($seax$),$ sedx

addl $20($seax$),$ gedx

addl $24($feax$),$ sedx

addl $28($feax$),$ fedx

add $1$$$32,$ qeax

addl $$8,$ qecx

cmpl fesi, fecx

j$1.$L$6$

Observe how register reax is being incremented by $32$ on each iteration.

Write $C$ code for a procedure combine $5px8$ that shows how pointers,

loop variables, and termination conditions are being computed by this code.

Show the general form with arbitrary data and combining operation in the

style of Figure $5\mathrm{.}19.$ Describe how it differs from our handwritten pointer code

$($Figure $5\mathrm{.}22).$