[PATCH] D115757: [SLP]Generalize cost model.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:5840
+    if (!I)
+      return true;
     auto *Op = cast<Instruction>(V)->getOperand(OpIdx);
----------------
RKSimon wrote:
> ABataev wrote:
> > RKSimon wrote:
> > > ABataev wrote:
> > > > RKSimon wrote:
> > > > > true?
> > > > Here is my idea. Generally speaking, here we can have only undef/poison or just a pointer (as part of getelementpr node) currently (maybe, need to add an assert). I thought that because of that we can treat its (virtual) operand as power-of-2, since it can be any value. Thoughts?
> > > Still not sure about this - this undef case is fine, but the GEP I can imagine might not work in all special cases.
> > > 
> > > How good is return isa<UndefValue>(V); instead?
> > GetElementPtr may have just a pointer, which is not a GEP instructions.
> > Say, we have this:
> > ```
> > void @foo(ptr %v) {
> > ...
> > load %v
> > %n = getelementptr i32, ptr v, 1
> > load %n
> > ...
> > }
> > ```
> > and we may have a ПУЗ node which includes {%v, %n}. Here %v is not a GEP though still part of the GEP node and we consider as `gentlementptr ptr %v, 0`.
> OK - so for GEPs you're saying that either the operands will be constant or a phi of constants?
No (or I missed something). I mean, that except for GEPs we may have just a non-ПУЗ pointer value and we just treat it as getelementptr, 0. But we return true if we have just a value (which is GEP with offset 0) and all other GEPs are power-of-2 constant ints.


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  https://reviews.llvm.org/D115757/new/

https://reviews.llvm.org/D115757