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An expression is available at a point if

  • A.it has been computed on every path and no operand has changed since
  • B.it has been computed on at least one of the paths reaching the point
  • C.all of its operands are compile time constants
  • D.it appears at least twice in the procedure being analysed

Answer: A

Available expressions is a forward analysis with intersection as its meet, because the value must be valid along every path. It is what justifies common subexpression elimination. An expression available on only some paths is a case for partial redundancy elimination.

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