> > Unfortunately there is 40% regression on mgrid with -flto (and also > > noticeable > > regression without LTO). First thing I noticed is that we stop omitting > > frame > > pointer in the hottest function. This is because we see: > > Does it happen with both 32-bit and 64-bit? No, 32bit only. > > > (set (reg/f:SI 7 sp) > > (plus:SI (reg/f:SI 7 sp) > > (const_int -8 [0xfffffffffffffff8]))) > > > > and we end up marking SP as as uneliminable in: > > > > /* See if this is setting the replacement hard register for > > an elimination. > > > > If DEST is the hard frame pointer, we do nothing because > > we assume that all assignments to the frame pointer are > > for non-local gotos and are being done at a time when > > they are valid and do not disturb anything else. Some > > machines want to eliminate a fake argument pointer (or > > even a fake frame pointer) with either the real frame > > pointer or the stack pointer. Assignments to the hard > > frame pointer must not prevent this elimination. */ > > > > for (ep = reg_eliminate; > > ep < ®_eliminate[NUM_ELIMINABLE_REGS]; > > ep++) > > if (ep->to_rtx == SET_DEST (x) > > && SET_DEST (x) != hard_frame_pointer_rtx > > && (! (SUPPORTS_STACK_ALIGNMENT && stack_realign_fp > > && REGNO (ep->to_rtx) == STACK_POINTER_REGNUM) > > || GET_CODE (SET_SRC (x)) != PLUS > > || XEXP (SET_SRC (x), 0) != SET_DEST (x) > > || ! CONST_INT_P (XEXP (SET_SRC (x), 1)))) > > setup_can_eliminate (ep, false); > > > > It is because of > > > > && (! (SUPPORTS_STACK_ALIGNMENT && stack_realign_fp > > && REGNO (ep->to_rtx) == STACK_POINTER_REGNUM) > > > > I am somewhat confused why do we need to stop eliminating. Function is not > > marked as needing drap (and in that case stack_realign_fp would be true) > > What is this conditional shooting for? > > Why is stack_realign_fp true? It is false, but htere is ! in the conditional.
Honza > > > -- > H.J.
