Refactor isPointerOffset (NFC).

[eugenis]

Summary

Simplify the API using Optional<> and address comments in

https://reviews.llvm.org/D66165

[vitalybuka]

llvm/include/llvm/Analysis/ValueTracking.h

667

const Value *Ptr1?

[eugenis]

address comments

llvm/include/llvm/Analysis/ValueTracking.h

Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
                                     unsigned Depth = 0);
 
   /// Return the boolean condition value in the context of the given instruction
   /// if it is known based on dominating conditions.
   Optional<bool> isImpliedByDomCondition(const Value *Cond,
                                          const Instruction *ContextI,
                                          const DataLayout &DL);
 
-  /// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and
-  /// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2
-  /// might be &A[40]. In this case offset would be -8.
-  bool isPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
+  /// If Ptr1 is provably equal to Ptr2 plus a constant offset, return that
+  /// offset. For example, Ptr1 might be &A[42], and Ptr2 might be &A[40]. In
+  /// this case offset would be -8.
+  Optional<int64_t> isPointerOffset(Value *Ptr1, Value *Ptr2,
                                     const DataLayout &DL);
 } // end namespace llvm
 
 #endif // LLVM_ANALYSIS_VALUETRACKING_H

llvm/lib/Analysis/ValueTracking.cpp

ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) {
 
   if (auto *I = dyn_cast<Instruction>(V))
     if (auto *Range = IIQ.getMetadata(I, LLVMContext::MD_range))
       CR = CR.intersectWith(getConstantRangeFromMetadata(*Range));
 
   return CR;
 }
 
-static int64_t getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
-                                  bool &VariableIdxFound,
-                                  const DataLayout &DL) {
+static Optional<int64_t>
+getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx, const DataLayout &DL) {
   // Skip over the first indices.
   gep_type_iterator GTI = gep_type_begin(GEP);
   for (unsigned i = 1; i != Idx; ++i, ++GTI)
     /*skip along*/;
 
   // Compute the offset implied by the rest of the indices.
   int64_t Offset = 0;
   for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
     ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
     if (!OpC)
-      return VariableIdxFound = true;
+      return None;
     if (OpC->isZero())
       continue; // No offset.
 
     // Handle struct indices, which add their field offset to the pointer.
     if (StructType *STy = GTI.getStructTypeOrNull()) {
       Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
       continue;
     }
 
     // Otherwise, we have a sequential type like an array or vector.  Multiply
     // the index by the ElementSize.
     uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
     Offset += Size * OpC->getSExtValue();
   }
 
   return Offset;
 }
 
-bool llvm::isPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
+Optional<int64_t> llvm::isPointerOffset(Value *Ptr1, Value *Ptr2,
                                         const DataLayout &DL) {
   Ptr1 = Ptr1->stripPointerCasts();
   Ptr2 = Ptr2->stripPointerCasts();
 
   // Handle the trivial case first.
   if (Ptr1 == Ptr2) {
-    Offset = 0;
-    return true;
+    return 0;
   }
 
   GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
   GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
 
-  bool VariableIdxFound = false;
-
   // If one pointer is a GEP and the other isn't, then see if the GEP is a
   // constant offset from the base, as in "P" and "gep P, 1".
   if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
-    Offset = -getOffsetFromIndex(GEP1, 1, VariableIdxFound, DL);
-    return !VariableIdxFound;
+    auto Offset = getOffsetFromIndex(GEP1, 1, DL);
+    if (!Offset)
+      return None;
+    return -*Offset;
   }
 
   if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
-    Offset = getOffsetFromIndex(GEP2, 1, VariableIdxFound, DL);
-    return !VariableIdxFound;
+    return getOffsetFromIndex(GEP2, 1, DL);
   }
 
   // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
   // base.  After that base, they may have some number of common (and
   // potentially variable) indices.  After that they handle some constant
   // offset, which determines their offset from each other.  At this point, we
   // handle no other case.
   if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
-    return false;
+    return None;
 
   // Skip any common indices and track the GEP types.
   unsigned Idx = 1;
   for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
     if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
       break;
 
-  int64_t Offset1 = getOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL);
-  int64_t Offset2 = getOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL);
-  if (VariableIdxFound)
-    return false;
-
-  Offset = Offset2 - Offset1;
-  return true;
+  auto Offset1 = getOffsetFromIndex(GEP1, Idx, DL);
+  auto Offset2 = getOffsetFromIndex(GEP2, Idx, DL);
+  if (!Offset1 || !Offset2)
+    return None;
+  return *Offset2 - *Offset1;
 }

llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
       // Check to see if this stored value is of the same byte-splattable value.
       Value *StoredByte = isBytewiseValue(NextStore->getOperand(0), DL);
       if (isa<UndefValue>(ByteVal) && StoredByte)
         ByteVal = StoredByte;
       if (ByteVal != StoredByte)
         break;
 
       // Check to see if this store is to a constant offset from the start ptr.
-      int64_t Offset;
-      if (!isPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset,
-                           DL))
+      Optional<int64_t> Offset =
+          isPointerOffset(StartPtr, NextStore->getPointerOperand(), DL);
+      if (!Offset)
         break;
 
-      Ranges.addStore(Offset, NextStore);
+      Ranges.addStore(*Offset, NextStore);
     } else {
       MemSetInst *MSI = cast<MemSetInst>(BI);
 
       if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
           !isa<ConstantInt>(MSI->getLength()))
         break;
 
       // Check to see if this store is to a constant offset from the start ptr.
-      int64_t Offset;
-      if (!isPointerOffset(StartPtr, MSI->getDest(), Offset, DL))
+      Optional<int64_t> Offset = isPointerOffset(StartPtr, MSI->getDest(), DL);
+      if (!Offset)
         break;
 
-      Ranges.addMemSet(Offset, MSI);
+      Ranges.addMemSet(*Offset, MSI);
     }
   }
 
   // If we have no ranges, then we just had a single store with nothing that
   // could be merged in.  This is a very common case of course.
   if (Ranges.empty())
     return nullptr;