Consider the following code: int foo() { for (int y = 0; !y;) for (/*decl*/; !y; ++y) return 1; } This generates a -Wreturn-type warning, despite that the inner loop body will *always* execute. Moreover, with optimization enabled, the compiler does (as expected) successfully remove the loops entirely. (This is a simplified version of a pre-C++17 `with` statement. The purpose of this code, which is usually a macro, is to look like the opening statement of a block, where `/*decl*/` — omitted in this example — is in scope only until the end of the block. FWIW, the C++17 form, `if (/*decl*/; true)` does not exhibit the problem.) Live example: https://godbolt.org/g/5xM6C3. Possibly related to #67629 and/or #85914.
The warning happens in the front-end, so there is no concept of always-executed. You don't need a loop. This also warns. int foo() { int y=0; if (!y) return 1; } *** This bug has been marked as a duplicate of bug 67629 ***