CODEWITHSUNDEEP
cstaticlocalcompiler-optimization
Eric Martin
Eric Martin

Reputation: 69

Is it legal for a C compiler to optimize out local static variables?

For a function like

int test(void) {
  static int x = 0;
  x++;
  return 0;
}

is a C compiler allowed to optimize out x?

For reference, neither GCC 6.3.0 or Clang 3.9 optimize out incrementing x with -O3.

Upvotes: 5

Views: 415

Answers (1)

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272517

The compiler would be within its rights to optimise away this function completely, given it has no observable side effects (from the point of view of the C standard).

As to why your compilers aren't doing so, I can't explain that! (Though of course, they're under no obligation to do so.)

Upvotes: 2

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