[PATCH] D27518: Moving isComplex decision to TTI

[Michael Kuperstein via Phabricator via llvm-commits]

mkuper added inline comments.


================
Comment at: include/llvm/Analysis/TargetTransformInfo.h:606
+  /// of address-computation cost 
+  struct AddressAccessInfo {
+    bool  isStrided;        /// True in case the access is strided (AddRec).
----------------
magabari wrote:
> mkuper wrote:
> > magabari wrote:
> > > mkuper wrote:
> > > > hfinkel wrote:
> > > > > mkuper wrote:
> > > > > > delena wrote:
> > > > > > > mkuper wrote:
> > > > > > > > delena wrote:
> > > > > > > > > Why do you need a struct? "Value *" will contain everything.
> > > > > > > > > 
> > > > > > > > > Value *Stride;
> > > > > > > > > 
> > > > > > > > > if (Stride == nullptr) - no stride,
> > > > > > > > > dyn_cast<ConstantInt>(Stride) - answers the question isConstant()
> > > > > > > > >  
> > > > > > > > IIUC, we don't necessarily have a Value* in hand, this originates from a SCEV, right?
> > > > > > > yes. We can use const SCEV*. 
> > > > > > I'm not sure passing a SCEV* to TTI makes sense, in terms of layering.
> > > > > I don't see why that should be a problem. The backends already depend on SCEV (and the rest of analysis) because of IR-level passes. TTI should definitely use SCEV where appropriate.
> > > > Never mind me, then. SCEV it is.
> > > passing only Value* has some cons and doesn't solve the general problem.
> > > 1. it depends on SCEV
> > > 2. currently we differentiate between strided and not strided access, but i think that there is more than those 2 cases so i thought creating some struct will be better approach
> > I agree a Value* is not appropriate.
> > I can live with either a struct or SCEV.
> SCEV can't replace the struct, since you still need more info.
> nullptr -> means default behavior
> struct->isStrided = false -> means after check it is not strided at all
> struct->isStrided = true -> you can look on the stride info or SCEV
> but SCEV can be part of the struct if needed.
> So in case there is no objections I prefer to go with struct which will contain bool and SCEV.
But aren't you figuring isStrided out based on the SCEV?
That is, if you pass a SCEV* S, it can be:
nullptr -> default
!isa<SCEVAddRecExpr>(S) -> not strided
isa<SCEVAddRecExpr>(S) -> strided?


https://reviews.llvm.org/D27518