[Alignment][NFC] Add DebugStr and operator*

[gchatelet]

Summary

Also updates files to use them.

This is patch is part of a series to introduce an Alignment type.
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2019-July/133851.html
See this patch for the introduction of the type: https://reviews.llvm.org/D64790

[courbet]

llvm/include/llvm/Support/Alignment.h

398

What is the meaning of Align(1) * 3 ?

[courbet]

llvm/include/llvm/Support/Alignment.h

398

My point is, I think what you want is an operator<<()

[gchatelet]

llvm/include/llvm/Support/Alignment.h

398

Since we return an Align (or MaybeAlign) the result have to be a power of two (or it will assert).
I can make it clear by requesting a power of two for Rhs.

I agree that a shift operator has the correct semantic and is less error prone but then the call site would be harder to understand from

MTI->setDestAlignment(I.getDestAlign() * DFSF.DFS.ShadowWidthBytes);
MTI->setSourceAlignment(I.getSourceAlign() * DFSF.DFS.ShadowWidthBytes);

to

MTI->setDestAlignment(I.getDestAlign() << Log2_64(DFSF.DFS.ShadowWidthBytes));
MTI->setSourceAlignment(I.getSourceAlign() << Log2_64(DFSF.DFS.ShadowWidthBytes));

WDYT?

[courbet]

llvm/include/llvm/Support/Alignment.h

398

Alright, makes sense.

llvm/include/llvm/Support/Alignment.h

inline bool operator<(MaybeAlign Lhs, Align Rhs) {
   ALIGN_CHECK_ISSET(Lhs);
   return Lhs && (*Lhs).value() < Rhs.value();
 }
 inline bool operator>(MaybeAlign Lhs, Align Rhs) {
   ALIGN_CHECK_ISSET(Lhs);
   return Lhs && (*Lhs).value() > Rhs.value();
 }
 
+inline Align operator*(Align Lhs, uint64_t Rhs) {
+  assert(Rhs > 0 && "Rhs must be positive");
+  return Align(Lhs.value() * Rhs);
+}
+
+inline MaybeAlign operator*(MaybeAlign Lhs, uint64_t Rhs) {
+  assert(Rhs > 0 && "Rhs must be positive");
+  return Lhs ? Lhs.getValue() * Rhs : MaybeAlign();
+}
+
 inline Align operator/(Align Lhs, uint64_t Divisor) {
   assert(llvm::isPowerOf2_64(Divisor) &&
          "Divisor must be positive and a power of 2");
   assert(Lhs != 1 && "Can't halve byte alignment");
   return Align(Lhs.value() / Divisor);
 }
 
 inline MaybeAlign operator/(MaybeAlign Lhs, uint64_t Divisor) {
   assert(llvm::isPowerOf2_64(Divisor) &&
          "Divisor must be positive and a power of 2");
   return Lhs ? Lhs.getValue() / Divisor : MaybeAlign();
 }
 
 inline Align max(MaybeAlign Lhs, Align Rhs) {
   return Lhs && *Lhs > Rhs ? *Lhs : Rhs;
 }
 
 inline Align max(Align Lhs, MaybeAlign Rhs) {
   return Rhs && *Rhs > Lhs ? *Rhs : Lhs;
 }
 
+#ifndef NDEBUG
+// For usage in LLVM_DEBUG macros.
+inline std::string DebugStr(const Align &A) {
+  return "Align(" + std::to_string(A.value()) + ")";
+}
+// For usage in LLVM_DEBUG macros.
+inline std::string DebugStr(const MaybeAlign &MA) {
+  if (MA)
+    return "MaybeAlign(" + std::to_string(MA->value()) + ")";
+  return "MaybeAlign(None)";
+}
+#endif
+
 #undef ALIGN_CHECK_ISPOSITIVE
 #undef ALIGN_CHECK_ISSET
 
 } // namespace llvm
 
 #endif // LLVM_SUPPORT_ALIGNMENT_H_

llvm/lib/CodeGen/MachineFrameInfo.cpp

if (MaxAlignment < Alignment)
     MaxAlignment = Alignment;
 }
 
 /// Clamp the alignment if requested and emit a warning.
 static inline Align clampStackAlignment(bool ShouldClamp, Align Alignment,
                                         Align StackAlignment) {
   if (!ShouldClamp || Alignment <= StackAlignment)
     return Alignment;
-  LLVM_DEBUG(dbgs() << "Warning: requested alignment " << Alignment.value()
-                    << " exceeds the stack alignment " << StackAlignment.value()
+  LLVM_DEBUG(dbgs() << "Warning: requested alignment " << DebugStr(Alignment)
+                    << " exceeds the stack alignment "
+                    << DebugStr(StackAlignment)
                     << " when stack realignment is off" << '\n');
   return StackAlignment;
 }
 
 int MachineFrameInfo::CreateStackObject(uint64_t Size, Align Alignment,
                                         bool IsSpillSlot,
                                         const AllocaInst *Alloca,
                                         uint8_t StackID) {

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

LLVM_DEBUG(
                   "object size\n");
     return;
   }
   Align RequiredAlignment = AI->getAlign().getValueOr(
       FuncInfo.MF->getDataLayout().getABITypeAlign(AI->getAllocatedType()));
   if (MFI.getObjectAlign(FixedIndex) < RequiredAlignment) {
     LLVM_DEBUG(dbgs() << "  argument copy elision failed: alignment of alloca "
                          "greater than stack argument alignment ("
-                      << RequiredAlignment.value() << " vs "
-                      << MFI.getObjectAlign(FixedIndex).value() << ")\n");
+                      << DebugStr(RequiredAlignment) << " vs "
+                      << DebugStr(MFI.getObjectAlign(FixedIndex)) << ")\n");
     return;
   }
 
   // Perform the elision. Delete the old stack object and replace its only use
   // in the variable info map. Mark the stack object as mutable.
   LLVM_DEBUG({
     dbgs() << "Eliding argument copy from " << Arg << " to " << *AI << '\n'
            << "  Replacing frame index " << OldIndex << " with " << FixedIndex

llvm/lib/Target/Mips/MipsRegisterInfo.cpp

eliminateFrameIndex(MachineBasicBlock::iterator II, int SPAdj,
   int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
   uint64_t stackSize = MF.getFrameInfo().getStackSize();
   int64_t spOffset = MF.getFrameInfo().getObjectOffset(FrameIndex);
 
   LLVM_DEBUG(errs() << "FrameIndex : " << FrameIndex << "\n"
                     << "spOffset   : " << spOffset << "\n"
                     << "stackSize  : " << stackSize << "\n"
                     << "alignment  : "
-                    << MF.getFrameInfo().getObjectAlign(FrameIndex).value()
+                    << DebugStr(MF.getFrameInfo().getObjectAlign(FrameIndex))
                     << "\n");
 
   eliminateFI(MI, FIOperandNum, FrameIndex, stackSize, spOffset);
 }
 
 Register MipsRegisterInfo::
 getFrameRegister(const MachineFunction &MF) const {
   const MipsSubtarget &Subtarget = MF.getSubtarget<MipsSubtarget>();

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

return AttributeList::get(
       CallSiteAttrs.getRetAttributes(),
       llvm::makeArrayRef(ArgumentAttributes));
 }
 
 class DataFlowSanitizer : public ModulePass {
   friend struct DFSanFunction;
   friend class DFSanVisitor;
 
-  enum {
-    ShadowWidth = 16
-  };
+  enum { ShadowWidthBits = 16, ShadowWidthBytes = ShadowWidthBits / 8 };
 
   /// Which ABI should be used for instrumented functions?
   enum InstrumentedABI {
     /// Argument and return value labels are passed through additional
     /// arguments and by modifying the return type.
     IA_Args,
 
     /// Argument and return value labels are passed through TLS variables
bool DataFlowSanitizer::doInitialization(Module &M) {
   bool IsMIPS64 = TargetTriple.isMIPS64();
   bool IsAArch64 = TargetTriple.getArch() == Triple::aarch64 ||
                    TargetTriple.getArch() == Triple::aarch64_be;
 
   const DataLayout &DL = M.getDataLayout();
 
   Mod = &M;
   Ctx = &M.getContext();
-  ShadowTy = IntegerType::get(*Ctx, ShadowWidth);
+  ShadowTy = IntegerType::get(*Ctx, ShadowWidthBits);
   ShadowPtrTy = PointerType::getUnqual(ShadowTy);
   IntptrTy = DL.getIntPtrType(*Ctx);
   ZeroShadow = ConstantInt::getSigned(ShadowTy, 0);
-  ShadowPtrMul = ConstantInt::getSigned(IntptrTy, ShadowWidth / 8);
+  ShadowPtrMul = ConstantInt::getSigned(IntptrTy, ShadowWidthBytes);
   if (IsX86_64)
     ShadowPtrMask = ConstantInt::getSigned(IntptrTy, ~0x700000000000LL);
   else if (IsMIPS64)
     ShadowPtrMask = ConstantInt::getSigned(IntptrTy, ~0xF000000000LL);
   // AArch64 supports multiple VMAs and the shadow mask is set at runtime.
   else if (IsAArch64)
     DFSanRuntimeShadowMask = true;
   else
Value *DFSanFunction::loadShadow(Value *Addr, uint64_t Size, uint64_t Align,
   if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
     const auto i = AllocaShadowMap.find(AI);
     if (i != AllocaShadowMap.end()) {
       IRBuilder<> IRB(Pos);
       return IRB.CreateLoad(DFS.ShadowTy, i->second);
     }
   }
 
-  const MaybeAlign ShadowAlign(Align * DFS.ShadowWidth / 8);
+  const MaybeAlign ShadowAlign(Align * DFS.ShadowWidthBytes);
   SmallVector<const Value *, 2> Objs;
   GetUnderlyingObjects(Addr, Objs, Pos->getModule()->getDataLayout());
   bool AllConstants = true;
   for (const Value *Obj : Objs) {
     if (isa<Function>(Obj) || isa<BlockAddress>(Obj))
       continue;
     if (isa<GlobalVariable>(Obj) && cast<GlobalVariable>(Obj)->isConstant())
       continue;
case 2: {
     IRBuilder<> IRB(Pos);
     Value *ShadowAddr1 = IRB.CreateGEP(DFS.ShadowTy, ShadowAddr,
                                        ConstantInt::get(DFS.IntptrTy, 1));
     return combineShadows(
         IRB.CreateAlignedLoad(DFS.ShadowTy, ShadowAddr, ShadowAlign),
         IRB.CreateAlignedLoad(DFS.ShadowTy, ShadowAddr1, ShadowAlign), Pos);
   }
   }
-  if (!AvoidNewBlocks && Size % (64 / DFS.ShadowWidth) == 0) {
+  if (!AvoidNewBlocks && Size % (64 / DFS.ShadowWidthBits) == 0) {
     // Fast path for the common case where each byte has identical shadow: load
     // shadow 64 bits at a time, fall out to a __dfsan_union_load call if any
     // shadow is non-equal.
     BasicBlock *FallbackBB = BasicBlock::Create(*DFS.Ctx, "", F);
     IRBuilder<> FallbackIRB(FallbackBB);
     CallInst *FallbackCall = FallbackIRB.CreateCall(
         DFS.DFSanUnionLoadFn,
         {ShadowAddr, ConstantInt::get(DFS.IntptrTy, Size)});
     FallbackCall->addAttribute(AttributeList::ReturnIndex, Attribute::ZExt);
 
     // Compare each of the shadows stored in the loaded 64 bits to each other,
-    // by computing (WideShadow rotl ShadowWidth) == WideShadow.
+    // by computing (WideShadow rotl ShadowWidthBits) == WideShadow.
     IRBuilder<> IRB(Pos);
     Value *WideAddr =
         IRB.CreateBitCast(ShadowAddr, Type::getInt64PtrTy(*DFS.Ctx));
     Value *WideShadow =
         IRB.CreateAlignedLoad(IRB.getInt64Ty(), WideAddr, ShadowAlign);
     Value *TruncShadow = IRB.CreateTrunc(WideShadow, DFS.ShadowTy);
-    Value *ShlShadow = IRB.CreateShl(WideShadow, DFS.ShadowWidth);
-    Value *ShrShadow = IRB.CreateLShr(WideShadow, 64 - DFS.ShadowWidth);
+    Value *ShlShadow = IRB.CreateShl(WideShadow, DFS.ShadowWidthBits);
+    Value *ShrShadow = IRB.CreateLShr(WideShadow, 64 - DFS.ShadowWidthBits);
     Value *RotShadow = IRB.CreateOr(ShlShadow, ShrShadow);
     Value *ShadowsEq = IRB.CreateICmpEQ(WideShadow, RotShadow);
 
     BasicBlock *Head = Pos->getParent();
     BasicBlock *Tail = Head->splitBasicBlock(Pos->getIterator());
 
     if (DomTreeNode *OldNode = DT.getNode(Head)) {
       std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
 
       DomTreeNode *NewNode = DT.addNewBlock(Tail, Head);
       for (auto Child : Children)
         DT.changeImmediateDominator(Child, NewNode);
     }
 
     // In the following code LastBr will refer to the previous basic block's
     // conditional branch instruction, whose true successor is fixed up to point
     // to the next block during the loop below or to the tail after the final
     // iteration.
     BranchInst *LastBr = BranchInst::Create(FallbackBB, FallbackBB, ShadowsEq);
     ReplaceInstWithInst(Head->getTerminator(), LastBr);
     DT.addNewBlock(FallbackBB, Head);
 
-    for (uint64_t Ofs = 64 / DFS.ShadowWidth; Ofs != Size;
-         Ofs += 64 / DFS.ShadowWidth) {
+    for (uint64_t Ofs = 64 / DFS.ShadowWidthBits; Ofs != Size;
+         Ofs += 64 / DFS.ShadowWidthBits) {
       BasicBlock *NextBB = BasicBlock::Create(*DFS.Ctx, "", F);
       DT.addNewBlock(NextBB, LastBr->getParent());
       IRBuilder<> NextIRB(NextBB);
       WideAddr = NextIRB.CreateGEP(Type::getInt64Ty(*DFS.Ctx), WideAddr,
                                    ConstantInt::get(DFS.IntptrTy, 1));
       Value *NextWideShadow = NextIRB.CreateAlignedLoad(NextIRB.getInt64Ty(),
                                                         WideAddr, ShadowAlign);
       ShadowsEq = NextIRB.CreateICmpEQ(WideShadow, NextWideShadow);
if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
     const auto i = AllocaShadowMap.find(AI);
     if (i != AllocaShadowMap.end()) {
       IRBuilder<> IRB(Pos);
       IRB.CreateStore(Shadow, i->second);
       return;
     }
   }
 
-  const Align ShadowAlign(Alignment.value() * (DFS.ShadowWidth / 8));
+  const Align ShadowAlign(Alignment.value() * DFS.ShadowWidthBytes);
   IRBuilder<> IRB(Pos);
   Value *ShadowAddr = DFS.getShadowAddress(Addr, Pos);
   if (Shadow == DFS.ZeroShadow) {
-    IntegerType *ShadowTy = IntegerType::get(*DFS.Ctx, Size * DFS.ShadowWidth);
+    IntegerType *ShadowTy =
+        IntegerType::get(*DFS.Ctx, Size * DFS.ShadowWidthBits);
     Value *ExtZeroShadow = ConstantInt::get(ShadowTy, 0);
     Value *ExtShadowAddr =
         IRB.CreateBitCast(ShadowAddr, PointerType::getUnqual(ShadowTy));
     IRB.CreateAlignedStore(ExtZeroShadow, ExtShadowAddr, ShadowAlign);
     return;
   }
 
-  const unsigned ShadowVecSize = 128 / DFS.ShadowWidth;
+  const unsigned ShadowVecSize = 128 / DFS.ShadowWidthBits;
   uint64_t Offset = 0;
   if (Size >= ShadowVecSize) {
     VectorType *ShadowVecTy = VectorType::get(DFS.ShadowTy, ShadowVecSize);
     Value *ShadowVec = UndefValue::get(ShadowVecTy);
     for (unsigned i = 0; i != ShadowVecSize; ++i) {
       ShadowVec = IRB.CreateInsertElement(
           ShadowVec, Shadow, ConstantInt::get(Type::getInt32Ty(*DFS.Ctx), i));
     }
IRB.CreateCall(DFSF.DFS.DFSanSetLabelFn,
                                                                 *DFSF.DFS.Ctx)),
                   IRB.CreateZExtOrTrunc(I.getLength(), DFSF.DFS.IntptrTy)});
 }
 
 void DFSanVisitor::visitMemTransferInst(MemTransferInst &I) {
   IRBuilder<> IRB(&I);
   Value *RawDestShadow = DFSF.DFS.getShadowAddress(I.getDest(), &I);
   Value *SrcShadow = DFSF.DFS.getShadowAddress(I.getSource(), &I);
-  Value *LenShadow = IRB.CreateMul(
-      I.getLength(),
-      ConstantInt::get(I.getLength()->getType(), DFSF.DFS.ShadowWidth / 8));
+  Value *LenShadow =
+      IRB.CreateMul(I.getLength(), ConstantInt::get(I.getLength()->getType(),
+                                                    DFSF.DFS.ShadowWidthBytes));
   Type *Int8Ptr = Type::getInt8PtrTy(*DFSF.DFS.Ctx);
   Value *DestShadow = IRB.CreateBitCast(RawDestShadow, Int8Ptr);
   SrcShadow = IRB.CreateBitCast(SrcShadow, Int8Ptr);
   auto *MTI = cast<MemTransferInst>(
       IRB.CreateCall(I.getFunctionType(), I.getCalledValue(),
                      {DestShadow, SrcShadow, LenShadow, I.getVolatileCst()}));
   if (ClPreserveAlignment) {
-    MTI->setDestAlignment(I.getDestAlignment() * (DFSF.DFS.ShadowWidth / 8));
-    MTI->setSourceAlignment(I.getSourceAlignment() * (DFSF.DFS.ShadowWidth / 8));
+    MTI->setDestAlignment(I.getDestAlign() * DFSF.DFS.ShadowWidthBytes);
+    MTI->setSourceAlignment(I.getSourceAlign() * DFSF.DFS.ShadowWidthBytes);
   } else {
-    MTI->setDestAlignment(DFSF.DFS.ShadowWidth / 8);
-    MTI->setSourceAlignment(DFSF.DFS.ShadowWidth / 8);
+    MTI->setDestAlignment(Align(DFSF.DFS.ShadowWidthBytes));
+    MTI->setSourceAlignment(Align(DFSF.DFS.ShadowWidthBytes));
   }
   if (ClEventCallbacks) {
     IRB.CreateCall(DFSF.DFS.DFSanMemTransferCallbackFn,
                    {RawDestShadow, I.getLength()});
   }
 }
 
 void DFSanVisitor::visitReturnInst(ReturnInst &RI) {

llvm/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp

 }
 
 // Given an expression for the (constant) alignment, AlignSCEV, and an
 // expression for the displacement between a pointer and the aligned address,
 // DiffSCEV, compute the alignment of the displaced pointer if it can be reduced
 // to a constant. Using SCEV to compute alignment handles the case where
 // DiffSCEV is a recurrence with constant start such that the aligned offset
 // is constant. e.g. {16,+,32} % 32 -> 16.
-static unsigned getNewAlignmentDiff(const SCEV *DiffSCEV,
+static MaybeAlign getNewAlignmentDiff(const SCEV *DiffSCEV,
                                       const SCEV *AlignSCEV,
                                       ScalarEvolution *SE) {
   // DiffUnits = Diff % int64_t(Alignment)
   const SCEV *DiffUnitsSCEV = SE->getURemExpr(DiffSCEV, AlignSCEV);
 
   LLVM_DEBUG(dbgs() << "\talignment relative to " << *AlignSCEV << " is "
                     << *DiffUnitsSCEV << " (diff: " << *DiffSCEV << ")\n");
 
   if (const SCEVConstant *ConstDUSCEV =
       dyn_cast<SCEVConstant>(DiffUnitsSCEV)) {
     int64_t DiffUnits = ConstDUSCEV->getValue()->getSExtValue();
 
     // If the displacement is an exact multiple of the alignment, then the
     // displaced pointer has the same alignment as the aligned pointer, so
     // return the alignment value.
     if (!DiffUnits)
-      return (unsigned)
-        cast<SCEVConstant>(AlignSCEV)->getValue()->getSExtValue();
+      return cast<SCEVConstant>(AlignSCEV)->getValue()->getAlignValue();
 
     // If the displacement is not an exact multiple, but the remainder is a
     // constant, then return this remainder (but only if it is a power of 2).
     uint64_t DiffUnitsAbs = std::abs(DiffUnits);
     if (isPowerOf2_64(DiffUnitsAbs))
-      return (unsigned) DiffUnitsAbs;
+      return Align(DiffUnitsAbs);
   }
 
-  return 0;
+  return None;
 }
 
 // There is an address given by an offset OffSCEV from AASCEV which has an
 // alignment AlignSCEV. Use that information, if possible, to compute a new
 // alignment for Ptr.
-static unsigned getNewAlignment(const SCEV *AASCEV, const SCEV *AlignSCEV,
+static MaybeAlign getNewAlignment(const SCEV *AASCEV, const SCEV *AlignSCEV,
                                   const SCEV *OffSCEV, Value *Ptr,
                                   ScalarEvolution *SE) {
   const SCEV *PtrSCEV = SE->getSCEV(Ptr);
   // On a platform with 32-bit allocas, but 64-bit flat/global pointer sizes
   // (*cough* AMDGPU), the effective SCEV type of AASCEV and PtrSCEV
   // may disagree. Trunc/extend so they agree.
   PtrSCEV = SE->getTruncateOrZeroExtend(
       PtrSCEV, SE->getEffectiveSCEVType(AASCEV->getType()));
   const SCEV *DiffSCEV = SE->getMinusSCEV(PtrSCEV, AASCEV);
 
   // On 32-bit platforms, DiffSCEV might now have type i32 -- we've always
   // sign-extended OffSCEV to i64, so make sure they agree again.
   DiffSCEV = SE->getNoopOrSignExtend(DiffSCEV, OffSCEV->getType());
 
   // What we really want to know is the overall offset to the aligned
   // address. This address is displaced by the provided offset.
   DiffSCEV = SE->getMinusSCEV(DiffSCEV, OffSCEV);
 
   LLVM_DEBUG(dbgs() << "AFI: alignment of " << *Ptr << " relative to "
                     << *AlignSCEV << " and offset " << *OffSCEV
                     << " using diff " << *DiffSCEV << "\n");
 
-  unsigned NewAlignment = getNewAlignmentDiff(DiffSCEV, AlignSCEV, SE);
-  LLVM_DEBUG(dbgs() << "\tnew alignment: " << NewAlignment << "\n");
+  if (MaybeAlign NewAlignment = getNewAlignmentDiff(DiffSCEV, AlignSCEV, SE)) {
+    LLVM_DEBUG(dbgs() << "\tnew alignment: " << DebugStr(NewAlignment) << "\n");
+    return *NewAlignment;
+  }
 
-  if (NewAlignment) {
-    return NewAlignment;
-  } else if (const SCEVAddRecExpr *DiffARSCEV =
-             dyn_cast<SCEVAddRecExpr>(DiffSCEV)) {
+  if (const SCEVAddRecExpr *DiffARSCEV = dyn_cast<SCEVAddRecExpr>(DiffSCEV)) {
     // The relative offset to the alignment assumption did not yield a constant,
     // but we should try harder: if we assume that a is 32-byte aligned, then in
     // for (i = 0; i < 1024; i += 4) r += a[i]; not all of the loads from a are
     // 32-byte aligned, but instead alternate between 32 and 16-byte alignment.
     // As a result, the new alignment will not be a constant, but can still
     // be improved over the default (of 4) to 16.
 
     const SCEV *DiffStartSCEV = DiffARSCEV->getStart();
     const SCEV *DiffIncSCEV = DiffARSCEV->getStepRecurrence(*SE);
 
     LLVM_DEBUG(dbgs() << "\ttrying start/inc alignment using start "
                       << *DiffStartSCEV << " and inc " << *DiffIncSCEV << "\n");
 
     // Now compute the new alignment using the displacement to the value in the
     // first iteration, and also the alignment using the per-iteration delta.
     // If these are the same, then use that answer. Otherwise, use the smaller
     // one, but only if it divides the larger one.
-    NewAlignment = getNewAlignmentDiff(DiffStartSCEV, AlignSCEV, SE);
-    unsigned NewIncAlignment = getNewAlignmentDiff(DiffIncSCEV, AlignSCEV, SE);
-
-    LLVM_DEBUG(dbgs() << "\tnew start alignment: " << NewAlignment << "\n");
-    LLVM_DEBUG(dbgs() << "\tnew inc alignment: " << NewIncAlignment << "\n");
+    MaybeAlign NewAlignment = getNewAlignmentDiff(DiffStartSCEV, AlignSCEV, SE);
+    MaybeAlign NewIncAlignment =
+        getNewAlignmentDiff(DiffIncSCEV, AlignSCEV, SE);
 
-    if (!NewAlignment || !NewIncAlignment) {
-      return 0;
-    } else if (NewAlignment > NewIncAlignment) {
-      if (NewAlignment % NewIncAlignment == 0) {
-        LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: " << NewIncAlignment
-                          << "\n");
-        return NewIncAlignment;
-      }
-    } else if (NewIncAlignment > NewAlignment) {
-      if (NewIncAlignment % NewAlignment == 0) {
-        LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: " << NewAlignment
-                          << "\n");
-        return NewAlignment;
-      }
-    } else if (NewIncAlignment == NewAlignment) {
-      LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: " << NewAlignment
-                        << "\n");
+    LLVM_DEBUG(dbgs() << "\tnew start alignment: " << DebugStr(NewAlignment)
+    LLVM_DEBUG(dbgs() << "\tnew inc alignment: " << DebugStr(NewIncAlignment)
+
+    // Both None or set to the same value.
+    if (NewAlignment == NewIncAlignment) {
+      LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: "
+                        << DebugStr(NewAlignment) << "\n");
+    if (NewAlignment > NewIncAlignment) {
+      LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: "
+                        << DebugStr(NewIncAlignment) << "\n");
+      return NewIncAlignment;
+    }
+    if (NewIncAlignment > NewAlignment) {
+      LLVM_DEBUG(dbgs() << "\tnew start/inc alignment: "
+                        << DebugStr(NewAlignment) << "\n");
       return NewAlignment;
     }
   }
 
-  return 0;
+  return None;
 }
 
 bool AlignmentFromAssumptionsPass::extractAlignmentInfo(CallInst *I,
                                                         Value *&AAPtr,
                                                         const SCEV *&AlignSCEV,
                                                         const SCEV *&OffSCEV) {
   // An alignment assume must be a statement about the least-significant
   // bits of the pointer being zero, possibly with some offset.
if (Instruction *K = dyn_cast<Instruction>(J))
       if (isValidAssumeForContext(ACall, K, DT))
         WorkList.push_back(K);
   }
 
   while (!WorkList.empty()) {
     Instruction *J = WorkList.pop_back_val();
 
     if (LoadInst *LI = dyn_cast<LoadInst>(J)) {
-      unsigned NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
+      MaybeAlign NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
                                                 LI->getPointerOperand(), SE);
 
       if (NewAlignment > LI->getAlignment()) {
         LI->setAlignment(MaybeAlign(NewAlignment));
         ++NumLoadAlignChanged;
       }
     } else if (StoreInst *SI = dyn_cast<StoreInst>(J)) {
-      unsigned NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
+      MaybeAlign NewAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
                                                 SI->getPointerOperand(), SE);
 
       if (NewAlignment > SI->getAlignment()) {
         SI->setAlignment(MaybeAlign(NewAlignment));
         ++NumStoreAlignChanged;
       }
     } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(J)) {
-      unsigned NewDestAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
-        MI->getDest(), SE);
+      MaybeAlign NewDestAlignment =
+          getNewAlignment(AASCEV, AlignSCEV, OffSCEV, MI->getDest(), SE);
 
-      LLVM_DEBUG(dbgs() << "\tmem inst: " << NewDestAlignment << "\n";);
+      LLVM_DEBUG(dbgs() << "\tmem inst: " << DebugStr(NewDestAlignment)
+                        << "\n";);
       if (NewDestAlignment > MI->getDestAlignment()) {
         MI->setDestAlignment(NewDestAlignment);
         ++NumMemIntAlignChanged;
       }
 
       // For memory transfers, there is also a source alignment that
       // can be set.
       if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
-        unsigned NewSrcAlignment = getNewAlignment(AASCEV, AlignSCEV, OffSCEV,
-          MTI->getSource(), SE);
+        MaybeAlign NewSrcAlignment =
+            getNewAlignment(AASCEV, AlignSCEV, OffSCEV, MTI->getSource(), SE);
 
-        LLVM_DEBUG(dbgs() << "\tmem trans: " << NewSrcAlignment << "\n";);
+        LLVM_DEBUG(dbgs() << "\tmem trans: " << DebugStr(NewSrcAlignment)
+                          << "\n";);
 
         if (NewSrcAlignment > MTI->getSourceAlignment()) {
           MTI->setSourceAlignment(NewSrcAlignment);
           ++NumMemIntAlignChanged;
         }
       }
     }