Sohail Aslam Compiler Construction Notes
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Here is the bottom-up parse of the assignment statement a = b*-c + b*-c and the
syntax-directed translation into three-address code.
Parser action attribute Three- address code
id=id โ โid + id โ โid
id=E1 โ โid + id โ โid E1.place = b
id=E1 โ โE2 + id โ โid E2.place = c
id=E1 โ E2 + id โ โid E2.place = t1 t1 = โ c
id=E1 + id โ โid E1.place = t2 t2 = bโt1
id=E1 + E2 โ โid E2.place = b
id=E1 + E2 โ โE3 E3.place = c
id=E1 + E2 โ E3 E3.place = t3 t3 = โ c
id=E1 + E2 E2.place = t4 t4 = bโt3
id=E1 E1.place = t5 t5 = t2+t4
S a = t5
Representing Linear Codes
Three-address codes are often implemented as a set of quadruples. Each quadruple has
four fields: an operator, two operands (or sources) and a destination. In C++, for
example, one can design a quadruple class and then declare a simple array of quadruples.
This leads to the following arrangement; the index of the array element acts as the
number of quadruple generated.
Target Op Arg1 Arg2
t1 โ 2
t2 โ y
t3 ร t1 t2
t4 โ x
t5 โ t4 t3
