[VPlan] Add VPRecipeBase::mayHaveSideEffects.

[a.elovikov]

LGTM, please wait a day or two to let others take a look.

[fhahn]

Rebase directly on top of main.

llvm/lib/Transforms/Vectorize/VPlan.h

const Instruction *getUnderlyingInstr() const {
     return cast<Instruction>(getVPValue()->getUnderlyingValue());
   }
 
   /// Method to support type inquiry through isa, cast, and dyn_cast.
   static inline bool classof(const VPDef *D) {
     // All VPDefs are also VPRecipeBases.
     return true;
   }
+
+  /// Returns true if the recipe may have side-effects.
+  bool mayHaveSideEffects() const;
 };
 
 inline bool VPUser::classof(const VPDef *Def) {
   return Def->getVPDefID() == VPRecipeBase::VPInstructionSC ||
          Def->getVPDefID() == VPRecipeBase::VPWidenSC ||
          Def->getVPDefID() == VPRecipeBase::VPWidenCallSC ||
          Def->getVPDefID() == VPRecipeBase::VPWidenSelectSC ||
          Def->getVPDefID() == VPRecipeBase::VPWidenGEPSC ||

llvm/lib/Transforms/Vectorize/VPlan.cpp

void VPRegionBlock::print(raw_ostream &O, const Twine &Indent,
   for (auto *BlockBase : depth_first(Entry)) {
     O << '\n';
     BlockBase->print(O, NewIndent, SlotTracker);
   }
   O << Indent << "}\n";
 }
 #endif
 
+bool VPRecipeBase::mayHaveSideEffects() const {
+  switch (getVPDefID()) {
+  case VPBlendSC:
+  case VPBranchOnMaskSC:
+  case VPWidenSC:
+  case VPWidenGEPSC:
+  case VPReductionSC:
+  case VPWidenSelectSC: {
+    const Instruction *I =
+        dyn_cast_or_null<Instruction>(getVPValue()->getUnderlyingValue());
+    (void)I;
+    assert((!I || !I->mayHaveSideEffects()) &&
+           "underlying instruction has side-effects");
+    return false;
+  }
+  case VPReplicateSC: {
+    auto *R = cast<VPReplicateRecipe>(this);
+    return R->getUnderlyingInstr()->mayHaveSideEffects();
+  }
+  default:
+    return true;
+  }
+}
+
 void VPRecipeBase::insertBefore(VPRecipeBase *InsertPos) {
   assert(!Parent && "Recipe already in some VPBasicBlock");
   assert(InsertPos->getParent() &&
          "Insertion position not in any VPBasicBlock");
   Parent = InsertPos->getParent();
   Parent->getRecipeList().insert(InsertPos->getIterator(), this);
 }