In computer science, three-address code[1] (often abbreviated to TAC or 3AC) is an intermediate code used by optimizing compilers to aid in the implementation of code-improving transformations. Each TAC instruction has at most three operands and is typically a combination of assignment and a binary operator. For example, t1 := t2 + t3. The name derives from the use of three operands in these statements even though instructions with fewer operands may occur.
Since three-address code is used as an intermediate language within compilers, the operands will most likely not be concrete memory addresses or processor registers, but rather symbolic addresses that will be translated into actual addresses during register allocation. It is also not uncommon that operand names are numbered sequentially since three-address code is typically generated by the compiler.
A refinement of three-address code is A-normal form (ANF).
Examplesedit
In three-address code, this would be broken down into several separate instructions. These instructions translate more easily to assembly language. It is also easier to detect common sub-expressions for shortening the code. In the following example, one calculation is composed of several smaller ones:
# Calculate one solution to the [[Quadratic equation]]. x = (-b + sqrt(b^2 - 4*a*c)) / (2*a)
t1 := b * b t2 := 4 * a t3 := t2 * c t4 := t1 - t3 t5 := sqrt(t4) t6 := 0 - b t7 := t5 + t6 t8 := 2 * a t9 := t7 / t8 x := t9
Three-address code may have conditional and unconditional jumps and methods of accessing memory. It may also have methods of calling functions, or it may reduce these to jumps. In this way, three-address code may be useful in control-flow analysis. In the following C-like example, a loop stores the squares of the numbers between 0 and 9:
...for(i=0;i<10;++i){b[i]=i*i;}...
t1 := 0 ; initialize i L1: if t1 >= 10 goto L2 ; conditional jump t2 := t1 * t1 ; square of i t3 := t1 * 4 ; word-align address t4 := b + t3 ; address to store i*i *t4 := t2 ; store through pointer t1 := t1 + 1 ; increase i goto L1 ; repeat loop L2:
^V., Aho, Alfred (1986). Compilers, principles, techniques, and tools. Sethi, Ravi., Ullman, Jeffrey D., 1942-. Reading, Mass.: Addison-Wesley Pub. Co. pp. 466. ISBN0201100886. OCLC 12285707.{{cite book}}: CS1 maint: multiple names: authors list (link)
April 10, 2024
three, address, code, computer, science, three, address, code, often, abbreviated, intermediate, code, used, optimizing, compilers, implementation, code, improving, transformations, each, instruction, most, three, operands, typically, combination, assignment, . In computer science three address code 1 often abbreviated to TAC or 3AC is an intermediate code used by optimizing compilers to aid in the implementation of code improving transformations Each TAC instruction has at most three operands and is typically a combination of assignment and a binary operator For example t1 t2 t3 The name derives from the use of three operands in these statements even though instructions with fewer operands may occur Since three address code is used as an intermediate language within compilers the operands will most likely not be concrete memory addresses or processor registers but rather symbolic addresses that will be translated into actual addresses during register allocation It is also not uncommon that operand names are numbered sequentially since three address code is typically generated by the compiler A refinement of three address code is A normal form ANF Examples editIn three address code this would be broken down into several separate instructions These instructions translate more easily to assembly language It is also easier to detect common sub expressions for shortening the code In the following example one calculation is composed of several smaller ones Calculate one solution to the Quadratic equation x b sqrt b 2 4 a c 2 a t1 b b t2 4 a t3 t2 c t4 t1 t3 t5 sqrt t4 t6 0 b t7 t5 t6 t8 2 a t9 t7 t8 x t9 Three address code may have conditional and unconditional jumps and methods of accessing memory It may also have methods of calling functions or it may reduce these to jumps In this way three address code may be useful in control flow analysis In the following C like example a loop stores the squares of the numbers between 0 and 9 for i 0 i lt 10 i b i i i t1 0 initialize i L1 if t1 gt 10 goto L2 conditional jump t2 t1 t1 square of i t3 t1 4 word align address t4 b t3 address to store i i t4 t2 store through pointer t1 t1 1 increase i goto L1 repeat loop L2 See also edit nbsp Computer programming portalIntermediate language Reduced instruction set computer Static single assignment form SSA References edit V Aho Alfred 1986 Compilers principles techniques and tools Sethi Ravi Ullman Jeffrey D 1942 Reading Mass Addison Wesley Pub Co pp 466 ISBN 0201100886 OCLC 12285707 a href Template Cite book html title Template Cite book cite book a CS1 maint multiple names authors list link Retrieved from https en wikipedia org w index php title Three address code amp oldid 1152049378, wikipedia, wiki, book, books, library,
