On Dec 17, 2007, at 11:40 AM, Bill Wendling wrote: > Hi Chris, > >>> +// M_MAY_HAVE_SIDE_EFFECTS - Set if this instruction *might* have >>> side effects, >>> +// e.g. load instructions. Note: This and M_NEVER_HAS_SIDE_EFFECTS >>> are mutually >>> +// exclusive. You can't set both! If neither flag is set, then the >>> instruction >>> +// *always* has side effects. >>> +const unsigned M_MAY_HAVE_SIDE_EFFECTS = 1 << 18; >>> + >>> +// M_NEVER_HAS_SIDE_EFFECTS - Set if this instruction *never* has >>> side effects, >>> +// e.g., xor on X86. Note: This and M_MAY_HAVE_SIDE_EFFECTS are >>> mutually >>> +// exclusive. You can't set both! If neither flag is set, then the >>> instruction >>> +// *always* has side effects. >>> +const unsigned M_NEVER_HAS_SIDE_EFFECTS = 1 << 19; >> >> As others have pointed out, we need to be much more clear about what >> these mean. Specifically, I'd list "NEVER" first (it is easier to >> explain). The pertinent point here is completely missing in the >> comments: this flag is set on an instruction where there is a side >> effect that is not captured by any *operands* of the instruction or >> *other flags*. Instructions that are "isBranch" instructions but >> have >> no other side effects should have M_NEVER_HAS_SIDE_EFFECTS set. This >> flag should only be set on an instruction when *all instances* of an >> instruction of that opcode have no side effects in this way. >> > I'm confused. If we set this for an instruction where there is a side
I am pretty sure he meant the opposite. If M_NEVER_HAS_SIDE_EFFECTS is set, that means the instruction would never have any side effects that are not captured in the operands. Evan > > effect that is not captured by any operands of the instr or other > flags, then it has a side effect, right? Or do you mean that we > *shouldn't* set it in this situation (which makes more sense to me)? > > -bw > _______________________________________________ > llvm-commits mailing list > llvm-commits@cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
