Reaching Definition Analysis
A definition d reaches end of a block iff either
- It is generated in the block
- It reaches block and not killed
Kill & gen known for each block. A program with N blocks has 2N equations with 2N unknowns and therefore, solution is possible.
- Use iterative forward bit vector approach
for each block B do
in(B) =
 ;
out(B) = gen(B)
endfor;
change = true;
while change do
change = false;
for each block B do
newin = S out(P)
if newin 6= in(B) then {
change = true;
in(B) = newin;
out(B) = in(B) - kill(B) S gen(B);
}
endfor
endwhile |
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