Possible Partial redundancy optimization using code duplication

[anirudha-commits]

Consider this case

if (condition1)
 C1
else
 C2
end if

if (condition2)
 C1
else
 C2
end if

Now we have a path where we have redundancy of C1 when both conditions are true. However llvm is unable to optimize this and computes C1 again. Godbolt example: https://godbolt.org/z/nvYq7dcee

Clubbing the conditions solves this problem

if (condition1)
 C1
  if (condition2)
   C1
  else
   C2
  end if
else
 C2
 if (condition2)
  C1
 else
  C2
 end if
end if

in this case, the values can be stored in registers.
Refer to section 2 in https://www.brainkart.com/article/Partial-Redundancy-Elimination_8195/ for elaboration: