https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99299
--- Comment #6 from Segher Boessenkool <segher at gcc dot gnu.org> --- (In reply to Richard Biener from comment #4) > I'm not sure what your proposed not noreturn trap() would do in terms of > IL semantics compared to a not specially annotated general call? Nothing I think? But __builtin_trap *is* very different: it ends BBs. > "recoverable" likely means resuming after the trap, not on an exception > path (so it'll not be a throw())? "recoverable" is super unclear. For example, on Power the hardware has a concept "recoverable interrupt", which set MSR[RI]=1, and traps never do. This is a very different concept as what is wanted here, which has nothing to do with recoverability, and is simply about not being an abort() (which __builtin_trap *is*!) > The only thing that might be useful to the middle-end would be marking > the function as not altering the memory state. But I suppose it should > still serve as a barrier for code motion of both loads and stores, even > of those loads/stores are known to not trap. The only magic we'd have > for this would be __attribute__((const,returns_twice)). Which likely > will be more detrimental to general optimization. > > So - what's the "sub-optimal code generation" you refer to from the > (presumably) volatile asm() you use for the trap? > > [yeah, asm() on GIMPLE is less optimized than a call] The rs6000 backend can optimise the used instructions: we have trap_if instructions, both with registers and with immediates. A single instruction can do a comparison and a conditional trap. This works great with __builtin_trap, *if* the kernel's trap handler has abort() semantics. __builtin_trap_no_abort() maybe?
