On Wed, Feb 29, 2012 at 6:02 PM, Aurelien Buhrig <aurelien.buhrig....@gmail.com> wrote: > Le 29/02/2012 17:08, Richard Guenther a écrit : >> On Wed, Feb 29, 2012 at 4:41 PM, Aurelien Buhrig >> <aurelien.buhrig....@gmail.com> wrote: >>> Le 29/02/2012 16:15, Richard Guenther a écrit : >>>> On Wed, Feb 29, 2012 at 4:08 PM, Aurelien Buhrig >>>> <aurelien.buhrig....@gmail.com> wrote: >>>>> >>>>>> The issue is most probably that on GIMPLE we only deal with ptr_mode, >>>>>> not Pmode, and IVOPTs thinks that pointer induction variables will >>>>>> have ptr_mode. To fix this the cost computation would need to take >>>>>> into account ptr_mode to Pmode conversions _and_ would need to >>>>>> consider Pmode IVs in the first place (I'm not sure that will be easy). >>>>> >>>>> >>>>> Thank you Richard for you reply. >>>>> >>>>> I guess such an issue is not in the top priority tasks of main >>>>> developers. So I think I'll have to look at it myself if I feel >>>>> confident enough to carry out such a job (I've never worked at tree >>>>> level). >>>>> >>>>> My main wonder is about Pmode IVs: since GIMPLE representation only >>>>> deals with ptr_mode, what differentiates a Pmode IV from a ptr_mode one? >>>> >>>> Its TREE_TYPE. In your case you'd have a POINTER_TYPE with >>>> PSImode for Pmode and a POINTER_TYPE with SImode for ptr_mode >>>> pointers. They will differ in TYPE_MODE and TYPE_PRECISION. >>> >>> Thanks, I will look at it. >>> >>>>> BTW, this wonder is not limited to IVs. What does control the choice of >>>>> Pmode vs ptr_mode when mapping to RTL? >>>> >>>> ptr_mode is the C language specified mode for all pointers. Pmode is >>>> the mode used for pointers in address operands of CPU instructions. >>>> Usually they are the same. When mapping to RTL all ptr_mode uses >>>> for memory accesses are translated to Pmode while operations on >>>> the value of ptr_mode quantities are done on ptr_mode (IIRC). >>> >>> Another point that is not optimal for my backend is when computing the >>> address of an array element (M[i]). Now, both the M address and i are >>> extended to ptr_mode and the sum is truncated in Pmode; whereas it would >>> be much better to extend i to Pmode, and then perform the add in Pmode. >>> So if I understand correctly, the later option cannot be generated. Right? >> >> Not by IVOPTs at least. There is also the long-standing issue that >> POINTER_PLUS_EXPR only accepts sizetype offsets - that may cause >> issues if your target does not define sizetype having the same mode as >> ptr_mode. (And of course complicates using Pmode on the gimple level) > > Sorry, it wasn't related to ivopts, but on the use of Pmode from Gimple, > and especially when computing a M[i] address. (My ptr_mode and SIZE_TYPE > mode are the same). Can you confirm that it's not possible to compute > the address of M[i] in Pmode without truncating from ptr_mode? Because > mapping POINTER_PLUS_EXPR directly to Pmode would also be (with ivopts > PSI support) a great improvement for Pmode=PSImode targets.
Not sure what you mean with "not possible", it's not done. Richard. > Thanks for your help, > Aurélien > >> Richard. >> >>>> Richard. >>>> >>>>> Thanks, >>>>> Aurélien >>>>> >>> >
