> It's literally undecidable in principle whether some assembler correctly restores some register R. No, it's literally undecidable in principle whether every

> It's literally undecidable in principle whether some assembler correctly restores some register R. No, it's literally undecidable in principle whether every bit of assembler correctly restores some register R. For any given bit of inline assembler, it's quite likely to be trivial. In any case, we can have a useful safety feature without requiring the compiler to decide. The compiler can easily work out all the registers which get written to (right?), just not which get restored. So in addition to the clobber list, we could have a list of registers which the programmer asserts that the code restores. A register which is written to has to be on either the clobber list or the restore list (or be an output). This certainly isn't foolproof, but it would catch accidental clobbers.