jdoerfert added inline comments.
================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUAttributor.cpp:566
+ return false;
+ };
+
----------------
sameerds wrote:
> jdoerfert wrote:
> > jdoerfert wrote:
> > > sameerds wrote:
> > > > jdoerfert wrote:
> > > > > You can use AAPointerInfo for the call site return IRPosition. It
> > > > > will (through the iterations) gather all accesses and put them into
> > > > > "bins" based on offset and size. It deals with uses in calls, etc.
> > > > > and if there is stuff missing it is better to add it in one place so
> > > > > we benefit throughout.
> > > > I am not following what you have in mind. "implicitarg_ptr" is a
> > > > pointer returned by an intrinsic that reads an ABI-defined register. I
> > > > need to check that for a given call-graph, a particular range of bytes
> > > > relative to that base pointer are never accessed. The above DFS on the
> > > > uses conservatively assumes that such a load exists unless it can
> > > > conclusively trace every use of the base pointer. This may include the
> > > > pointer being passed to an extern function or being stored into a
> > > > different memory location (although we don't expect ABI registers being
> > > > capture this way). I am not seeing how to construct this around
> > > > AAPointerInfo. As far as I can see, the public interface only talks
> > > > about uses that are recognized as loads and stores.
> > > Not actually tested, replaces the function body. Depends on D119249.
> > > ```
> > > const auto PointerInfoAA = A.getAAFor<AAPointerInfo>(*this,
> > > IRPosition::callback_returned(cast<CallBase>(Ptr)), DepClassTy::Required);
> > > if (!PointerInfoAA.getState().isValidState())
> > > return true; // Abort (which is weird as false is abort in the other
> > > CB).
> > > AAPointerInfo::OffsetAndSize OAS(*Position, /* probably look pointer
> > > width up in DL */ 8);
> > > return !forallInterferingAccesses(OAS, [](const AAPointerInfo::Access
> > > &Acc, bool IsExact) {
> > > return Acc.getRemoteInst()->isDroppable(); });
> > > ```
> > You don't actually need the state check.
> > And as I said, this will take care of following pointers passed into
> > callees or through memory to other places, all while ignoring dead code,
> > etc.
> I see now. forallInterferingAccesses() does check for valid state on entry,
> which is sufficient to take care of all the opaque uses like a call to an
> extern function or a complicated phi or a capturing store. Thanks a ton ...
> this has been very educational!
Yes, all "forAll" functions will return `false` if we cannot visit "all".
Though, these methods will utilize the smarts, e.g., ignore what is dead, look
at loads if the value is stored in a way we can track it through memory,
transfer accesses in a callee to the caller "space" if a pointer is passed to
the callee,... etc.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D119216/new/
https://reviews.llvm.org/D119216
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