[llvm] [VPlan] Extract reverse interleave pointer adjustment into VPReverseInterleavePtrRecipe (PR #144864)

[Mel Chen via llvm-commits]

================
@@ -3223,25 +3251,6 @@ void VPInterleaveRecipe::execute(VPTransformState &State) {
   if (auto *I = dyn_cast<Instruction>(ResAddr))
     State.setDebugLocFrom(I->getDebugLoc());
 
-  // If the group is reverse, adjust the index to refer to the last vector lane
-  // instead of the first. We adjust the index from the first vector lane,
-  // rather than directly getting the pointer for lane VF - 1, because the
-  // pointer operand of the interleaved access is supposed to be uniform.
-  if (Group->isReverse()) {
-    Value *RuntimeVF =
-        getRuntimeVF(State.Builder, State.Builder.getInt32Ty(), State.VF);
-    Value *Index =
-        State.Builder.CreateSub(RuntimeVF, State.Builder.getInt32(1));
-    Index = State.Builder.CreateMul(Index,
-                                    State.Builder.getInt32(Group->getFactor()));
-    Index = State.Builder.CreateNeg(Index);
-
-    bool InBounds = false;
-    if (auto *Gep = dyn_cast<GetElementPtrInst>(ResAddr->stripPointerCasts()))
-      InBounds = Gep->isInBounds();
----------------
Mel-Chen wrote:

@alexey-bataev @fhahn The GEPNoWrapFlags setting for reverse interleave access doesn't seem to account for tail folding by mask. Could it have the same issue as noted in VPVectorEndPointerRecipe?
```
        // When folding the tail, we may compute an address that we don't in the
        // original scalar loop and it may not be inbounds. Drop Inbounds in that
        // case.
        GEPNoWrapFlags Flags =
            (CM.foldTailByMasking() || !GEP || !GEP->isInBounds())
                ? GEPNoWrapFlags::none()
                : GEPNoWrapFlags::inBounds();
```

https://github.com/llvm/llvm-project/pull/144864