On Tue, Jun 18, 2013 at 3:52 AM, Oleg Endo <oleg.e...@t-online.de> wrote: > On Mon, 2013-06-17 at 10:41 +0200, Eric Botcazou wrote: >> > My mistake. It's because arm_legitimize_address cannot re-factor "[r105 + >> > r165*4 + (-2064)]" into "rx = r105 + (-2064); [rx + r165*4]". Do you >> > suggest that this kind of transformation should be done in backend? I can >> > think of some disadvantages by doing it in backend: >> > Different kinds of address expression might be wanted in different phase of >> > compilation, for example, sometimes GCC wants to force computation of >> > address expression out of memory access because it cannot CSE array >> > indexing. It's difficult to differentiate in backend. >> >> It's equally difficult in memory_address_addr_space and it affects all the >> architectures at once... You said in the original message that Thumb2 and >> ARM >> modes are already not equally sensitive to it, so it's not unthinkable that >> some architectures might not want it at all. Therefore, yes, this should >> preferably be handled in arm_legitimize_address. > > My observation is, that legitimizing addressing modes in the backend by > looking at one isolated address works, but doesn't give good results. > In the SH backend there is this a particular case with displacement > addressing (register + constant). On SH displacements for byte > addressing are 0..15, 0..31 for 16 bit words and 0..63 for 32 bit words. > sh_legitimize_address (or rather sh_find_mov_disp_adjust) uses a fixed > heuristic to satisfy the displacement constraint and splits out a plus > insn if needed to adjust the base address. Of course that fixed > heuristic doesn't work for some cases and thus sometimes results in > unnecessary base address adjustments. > I had the idea of replacing the current (partially defunct) auto-inc-dec > RTL pass with a more generic addressing mode selection pass: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56590 > > Any suggestions/comments/... are highly appreciated. > In PR56590, is PR50749 the only one that correlate with auto-inc-dec? Others seem just problems of wrong addressing mode.
And one point on PR50749, auto-inc-dec depends on ivopt to choose auto-increment candidate. Since you disabled ivopt, I bet GCC will miss lots of auto-increment opportunities. Thanks. bin -- Best Regards.
