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. Thanks for your help, Aurélien > Richard. > >>> Richard. >>> >>>> Thanks, >>>> Aurélien >>>> >>
