On 12/07/19 15:02, Arnd Bergmann wrote: > I think what happens here is that clang does not treat the return > code of track the return code of is_64_bit_mode() as a constant > expression, and therefore assumes that the if() condition > may or may not be true, for the purpose of determining whether > the variable is used without an inialization. This would hold even > if it later eliminates the code leading up to the if() in an optimization > stage. IS_ENABLED(CONFIG_X86_64) however is a constant > expression, so with the patch, it understands this. > > In contrast, gcc seems to perform all the inlining first, and > then see if some variable is used uninitialized in the final code. > This gives additional information to the compiler, but makes the > outcome less predictable since it depends on optimization flags > and architecture specific behavior. > > Both approaches have their own sets of false positive and false > negative warnings. True, on the other hand constant returns are not really rocket science. :) Maybe change is_long_mode to a macro if !CONFIG_X86_64? That would be better if clang likes it. Paolo
