Three-Address Code
Three-address code is a sequence of statements of the form:
x := y op z
where x, y, and z are names, constants, or compiler generated temporaries; op is any operator. Three-address code is a linearization of an abstract syntax tree. This approach requires compiler generated temporaries. It is abstract and leaves the hard work of temporary management to the code generator which maps temporaries to registers and generates code to use the registers effectively.
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Assignment Statement |
x := y op z |
x, y, z are names, constants, or compiler generated temporaries; op is any binary operator |
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x := op y |
op is a unary operator |
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Indexed Assignment |
x := y[i] |
x, y, i are data objects |
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Copy Statement |
x := y |
x, y |
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Unconditional jump |
goto L |
L is the label of the next statement to be executed |
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Conditional jump |
if x relop y goto L |
x |
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Procedure calls and returns |
param x |
x is a parameter |
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call p, n |
p is the procedure, n is the number of parameters |
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return y |
y is an optional return value |
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Address and pointer assignments |
x := &y *x := y |
x is set to the location of y x is set to the value at the location y |
Three-address statements are implemented as records with fields for the operator and operands. A quadruple (quad) is a record with four fields, op, arg1, arg2, result. The contents of the fields may be pointers to entries in the symbol table. Other forms of three-address code are triples and indirect triples. Neither of which are covered here.
Posted in Computer Science, Information Technology, Compiler Design, Compiler Design | 