Example: Copy Constant Propagation (CCP)

Variable V is a copy constant (i) if V is assigned a constant, or

(ii)if V is defined by a copy V:= is a copy constant

call Q

a = 0

b = a

c = b

Write b

A = b + c

Procedure Main

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2

3

4

5

6

7

f2(xa,xb,xc)=(0,xb,xc)

f3(xa,xb,xc)=(xa,xa,xc)

f4(xa,xb,xc)=(xa,xb,xb)

f6(xa,xb,xc)= (?,xb,xc)

Procedure P

entry

Write(a,b,c)

Read(b)

exit

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9

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F9(xa,xb,xc)=(xa,xb,xc)

F10(xa,xb,xc)=(xa,?,xc)

P

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