[el_pollo_diablo]

Sure, that sort of language-specific idiosyncrasy must be dealt with in the compiler's front-end. In TFA's C example, consider that their loop

  while (i <= x) {
      // ...
  }

just needs a slight transformation to

  while (1) {
      if (i > x)
          break;
      // ...
  }

and C11's special permission does not apply any more since the controlling expression has become constant.

Analyzes and optimizations in compiler backends often normalize those two loops to a common representation (e.g. control-flow graph) at some point, so whatever treatment that sees them differently must happen early on.

[pjmlp]

In theory, in practice it depends on the compiler.

It is no accident that there is ongoing discussion that clang should get its own IR, just like it happens with the other frontends, instead of spewing LLVM IR directly into the next phase.