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) Richard. >> Richard. >> >>> Thanks, >>> Aurélien >>> >
