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Constant Propagation Transformation: Difference between revisions
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Constant Propagation Transformation (view source)
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Constant propagation is an optimization technique used in compilers to improve execution efficiency by replacing variables with known constant values during compilation. If an expression consists entirely of constants or previously propagated values, it is evaluated at compile time and replaced with its computed result. This transformation reduces runtime computations, simplifies code, and enables further optimizations by minimizing unnecessary variable assignments. By eliminating redundant calculations, constant propagation enhances program performance while preserving its original behavior. | |||
==Constant Propagation in emmtrix Studio== | |||
emmtrix Studio can implement constant propagation using #pragma directives or via the GUI. ConstPropagation is a transformation that propagates all known variable values within the block it is applied to. If an expression consists of propagated values and of constants, it will itself be evaluated to and replaced with its constant value. | |||
All arithmetic operations are supported. Function calls are not supported | |||
===Typical Usage and Benefits=== | |||
ConstPropagation is typically used to generate a clearer code, to reduce complexity for dependency analysis and increase potential for better optimization possibilities. | |||
===Example=== | |||
The following code tests ConstPropagation applied to main function. In the given example, variables a, b and c are known. They are propagated to the rest of the body of | |||
main. <syntaxhighlight lang="c"> | |||
#pragma EMX_TRANSFORMATION ConstPropagation | |||
int main(void) { | |||
int a = 2; | |||
int b = a; | |||
int c, d; | |||
c = 2 + 2; | |||
d = b + c; | |||
return 0; | |||
} | |||
</syntaxhighlight>The following code is the generated code after the transformation has been applied.<syntaxhighlight lang="c"> | |||
int main(void) { | |||
int a = 2; | |||
int b = a; | |||
int c; | |||
int d; | |||
c = 4; | |||
d = 6; | |||
return 0; | |||
} | |||
</syntaxhighlight> | |||