http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55288
--- Comment #2 from Ryan Johnson <scovich at gmail dot com> 2012-11-12 21:11:43 UTC --- (In reply to comment #1) > Why don't just initialize the variable? It seems simpler than implementing yet > another special attribute in GCC. In the original program, the "variable" is a largish struct, the function is hot, and the 'valid' execution path is not the most common one. Avoiding unnecessary initialization there has a measurable impact on performance. Note that, in other parts of the code that gcc understands better, the initialization is unnecessary (no warning) and gets optimized away even if I do have it in place... much to my chagrin once, after I did a lot of work to refactor a complex function, only to realize that gcc emitted *exactly* the same machine code afterward, because it had already noticed and eliminated the dead stores. There's also a philosophical argument to be made... if we agree that all warnings subject to false positives should be supressible, the current mechanism for maybe-uninitialized is inadequate, and a variable attribute would resolve the issue very nicely. There's precedent for this: you *could* use #ifndef NDEBUG (or even pragma diagnostic) to avoid unused-variable warnings for helper variables used by multiple assertions scattered over a region of code, but setting ((unused)) on the offending variable is much easier to read and maintain, while still allowing other unused variables to be flagged properly.
