+/// expandAddToGEP - Expand an addition expression with a pointer type into
+/// a GEP instead of using ptrtoint+arithmetic+inttoptr. This helps
+/// BasicAliasAnalysis and other passes analyze the result. See the rules
+/// for getelementptr vs. inttoptr in
+/// http://llvm.org/docs/LangRef.html#pointeraliasing
+/// for details.
+///
+/// Design note: The correctness of using getelementptr here depends on
+/// ScalarEvolution not recognizing inttoptr and ptrtoint operators, as
+/// they may introduce pointer arithmetic which may not be safely converted
+/// into getelementptr.
+///
+/// Design note: It might seem desirable for this function to be more
+/// loop-aware. If some of the indices are loop-invariant while others
+/// aren't, it might seem desirable to emit multiple GEPs, keeping the
+/// loop-invariant portions of the overall computation outside the loop.
+/// However, there are a few reasons this is not done here. Hoisting simple
+/// arithmetic is a low-level optimization that often isn't very
+/// important until late in the optimization process. In fact, passes
+/// like InstructionCombining will combine GEPs, even if it means
+/// pushing loop-invariant computation down into loops, so even if the
+/// GEPs were split here, the work would quickly be undone. The
+/// LoopStrengthReduction pass, which is usually run quite late (and
+/// after the last InstructionCombining pass), takes care of hoisting
+/// loop-invariant portions of expressions, after considering what
+/// can be folded using target addressing modes.
+///
+Value *SCEVExpander::expandAddToGEP(const SCEV *const *op_begin,
+ const SCEV *const *op_end,
+ const PointerType *PTy,
+ const Type *Ty,
+ Value *V) {
+ const Type *ElTy = PTy->getElementType();
+ SmallVector<Value *, 4> GepIndices;
+ SmallVector<const SCEV *, 8> Ops(op_begin, op_end);
+ bool AnyNonZeroIndices = false;
+
+ // Split AddRecs up into parts as either of the parts may be usable
+ // without the other.
+ SplitAddRecs(Ops, Ty, SE);
+
+ // Descend down the pointer's type and attempt to convert the other
+ // operands into GEP indices, at each level. The first index in a GEP
+ // indexes into the array implied by the pointer operand; the rest of
+ // the indices index into the element or field type selected by the
+ // preceding index.
+ for (;;) {
+ // If the scale size is not 0, attempt to factor out a scale for
+ // array indexing.
+ SmallVector<const SCEV *, 8> ScaledOps;
+ if (ElTy->isSized()) {
+ const SCEV *ElSize = SE.getSizeOfExpr(ElTy);
+ if (!ElSize->isZero()) {
+ SmallVector<const SCEV *, 8> NewOps;
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
+ const SCEV *Op = Ops[i];
+ const SCEV *Remainder = SE.getIntegerSCEV(0, Ty);
+ if (FactorOutConstant(Op, Remainder, ElSize, SE, SE.TD)) {
+ // Op now has ElSize factored out.
+ ScaledOps.push_back(Op);
+ if (!Remainder->isZero())
+ NewOps.push_back(Remainder);
+ AnyNonZeroIndices = true;
+ } else {
+ // The operand was not divisible, so add it to the list of operands
+ // we'll scan next iteration.
+ NewOps.push_back(Ops[i]);
+ }
+ }
+ // If we made any changes, update Ops.
+ if (!ScaledOps.empty()) {
+ Ops = NewOps;
+ SimplifyAddOperands(Ops, Ty, SE);
+ }
+ }
+ }
+
+ // Record the scaled array index for this level of the type. If
+ // we didn't find any operands that could be factored, tentatively
+ // assume that element zero was selected (since the zero offset
+ // would obviously be folded away).
+ Value *Scaled = ScaledOps.empty() ?
+ Constant::getNullValue(Ty) :
+ expandCodeFor(SE.getAddExpr(ScaledOps), Ty);
+ GepIndices.push_back(Scaled);
+
+ // Collect struct field index operands.
+ while (const StructType *STy = dyn_cast<StructType>(ElTy)) {
+ bool FoundFieldNo = false;
+ // An empty struct has no fields.
+ if (STy->getNumElements() == 0) break;
+ if (SE.TD) {
+ // With TargetData, field offsets are known. See if a constant offset
+ // falls within any of the struct fields.
+ if (Ops.empty()) break;
+ if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[0]))
+ if (SE.getTypeSizeInBits(C->getType()) <= 64) {
+ const StructLayout &SL = *SE.TD->getStructLayout(STy);
+ uint64_t FullOffset = C->getValue()->getZExtValue();
+ if (FullOffset < SL.getSizeInBytes()) {
+ unsigned ElIdx = SL.getElementContainingOffset(FullOffset);
+ GepIndices.push_back(
+ ConstantInt::get(Type::getInt32Ty(Ty->getContext()), ElIdx));
+ ElTy = STy->getTypeAtIndex(ElIdx);
+ Ops[0] =
+ SE.getConstant(Ty, FullOffset - SL.getElementOffset(ElIdx));
+ AnyNonZeroIndices = true;
+ FoundFieldNo = true;
+ }
+ }
+ } else {
+ // Without TargetData, just check for an offsetof expression of the
+ // appropriate struct type.
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i)
+ if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Ops[i])) {
+ const Type *CTy;
+ Constant *FieldNo;
+ if (U->isOffsetOf(CTy, FieldNo) && CTy == STy) {
+ GepIndices.push_back(FieldNo);
+ ElTy =
+ STy->getTypeAtIndex(cast<ConstantInt>(FieldNo)->getZExtValue());
+ Ops[i] = SE.getConstant(Ty, 0);
+ AnyNonZeroIndices = true;
+ FoundFieldNo = true;
+ break;
+ }
+ }
+ }
+ // If no struct field offsets were found, tentatively assume that
+ // field zero was selected (since the zero offset would obviously
+ // be folded away).
+ if (!FoundFieldNo) {
+ ElTy = STy->getTypeAtIndex(0u);
+ GepIndices.push_back(
+ Constant::getNullValue(Type::getInt32Ty(Ty->getContext())));
+ }
+ }
+
+ if (const ArrayType *ATy = dyn_cast<ArrayType>(ElTy))
+ ElTy = ATy->getElementType();
+ else
+ break;
+ }
+
+ // If none of the operands were convertible to proper GEP indices, cast
+ // the base to i8* and do an ugly getelementptr with that. It's still
+ // better than ptrtoint+arithmetic+inttoptr at least.
+ if (!AnyNonZeroIndices) {
+ // Cast the base to i8*.
+ V = InsertNoopCastOfTo(V,
+ Type::getInt8PtrTy(Ty->getContext(), PTy->getAddressSpace()));
+
+ // Expand the operands for a plain byte offset.
+ Value *Idx = expandCodeFor(SE.getAddExpr(Ops), Ty);
+
+ // Fold a GEP with constant operands.
+ if (Constant *CLHS = dyn_cast<Constant>(V))
+ if (Constant *CRHS = dyn_cast<Constant>(Idx))
+ return ConstantExpr::getGetElementPtr(CLHS, &CRHS, 1);
+
+ // Do a quick scan to see if we have this GEP nearby. If so, reuse it.
+ unsigned ScanLimit = 6;
+ BasicBlock::iterator BlockBegin = Builder.GetInsertBlock()->begin();
+ // Scanning starts from the last instruction before the insertion point.
+ BasicBlock::iterator IP = Builder.GetInsertPoint();
+ if (IP != BlockBegin) {
+ --IP;
+ for (; ScanLimit; --IP, --ScanLimit) {
+ // Don't count dbg.value against the ScanLimit, to avoid perturbing the
+ // generated code.
+ if (isa<DbgInfoIntrinsic>(IP))
+ ScanLimit++;
+ if (IP->getOpcode() == Instruction::GetElementPtr &&
+ IP->getOperand(0) == V && IP->getOperand(1) == Idx)
+ return IP;
+ if (IP == BlockBegin) break;
+ }
+ }
+
+ // Save the original insertion point so we can restore it when we're done.
+ BasicBlock *SaveInsertBB = Builder.GetInsertBlock();
+ BasicBlock::iterator SaveInsertPt = Builder.GetInsertPoint();
+
+ // Move the insertion point out of as many loops as we can.
+ while (const Loop *L = SE.LI->getLoopFor(Builder.GetInsertBlock())) {
+ if (!L->isLoopInvariant(V) || !L->isLoopInvariant(Idx)) break;
+ BasicBlock *Preheader = L->getLoopPreheader();
+ if (!Preheader) break;
+
+ // Ok, move up a level.
+ Builder.SetInsertPoint(Preheader, Preheader->getTerminator());
+ }
+
+ // Emit a GEP.
+ Value *GEP = Builder.CreateGEP(V, Idx, "uglygep");
+ rememberInstruction(GEP);
+
+ // Restore the original insert point.
+ if (SaveInsertBB)
+ restoreInsertPoint(SaveInsertBB, SaveInsertPt);
+
+ return GEP;
+ }
+
+ // Save the original insertion point so we can restore it when we're done.
+ BasicBlock *SaveInsertBB = Builder.GetInsertBlock();
+ BasicBlock::iterator SaveInsertPt = Builder.GetInsertPoint();
+
+ // Move the insertion point out of as many loops as we can.
+ while (const Loop *L = SE.LI->getLoopFor(Builder.GetInsertBlock())) {
+ if (!L->isLoopInvariant(V)) break;
+
+ bool AnyIndexNotLoopInvariant = false;
+ for (SmallVectorImpl<Value *>::const_iterator I = GepIndices.begin(),
+ E = GepIndices.end(); I != E; ++I)
+ if (!L->isLoopInvariant(*I)) {
+ AnyIndexNotLoopInvariant = true;
+ break;
+ }
+ if (AnyIndexNotLoopInvariant)
+ break;
+
+ BasicBlock *Preheader = L->getLoopPreheader();
+ if (!Preheader) break;
+
+ // Ok, move up a level.
+ Builder.SetInsertPoint(Preheader, Preheader->getTerminator());
+ }
+
+ // Insert a pretty getelementptr. Note that this GEP is not marked inbounds,
+ // because ScalarEvolution may have changed the address arithmetic to
+ // compute a value which is beyond the end of the allocated object.
+ Value *Casted = V;
+ if (V->getType() != PTy)
+ Casted = InsertNoopCastOfTo(Casted, PTy);
+ Value *GEP = Builder.CreateGEP(Casted,
+ GepIndices.begin(),
+ GepIndices.end(),
+ "scevgep");
+ Ops.push_back(SE.getUnknown(GEP));
+ rememberInstruction(GEP);
+
+ // Restore the original insert point.
+ if (SaveInsertBB)
+ restoreInsertPoint(SaveInsertBB, SaveInsertPt);
+
+ return expand(SE.getAddExpr(Ops));
+}
+
+/// isNonConstantNegative - Return true if the specified scev is negated, but
+/// not a constant.
+static bool isNonConstantNegative(const SCEV *F) {
+ const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(F);
+ if (!Mul) return false;
+
+ // If there is a constant factor, it will be first.
+ const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0));
+ if (!SC) return false;
+
+ // Return true if the value is negative, this matches things like (-42 * V).
+ return SC->getValue()->getValue().isNegative();
+}
+
+/// PickMostRelevantLoop - Given two loops pick the one that's most relevant for
+/// SCEV expansion. If they are nested, this is the most nested. If they are
+/// neighboring, pick the later.
+static const Loop *PickMostRelevantLoop(const Loop *A, const Loop *B,
+ DominatorTree &DT) {
+ if (!A) return B;
+ if (!B) return A;
+ if (A->contains(B)) return B;
+ if (B->contains(A)) return A;
+ if (DT.dominates(A->getHeader(), B->getHeader())) return B;
+ if (DT.dominates(B->getHeader(), A->getHeader())) return A;
+ return A; // Arbitrarily break the tie.
+}
+
+/// GetRelevantLoop - Get the most relevant loop associated with the given
+/// expression, according to PickMostRelevantLoop.
+static const Loop *GetRelevantLoop(const SCEV *S, LoopInfo &LI,
+ DominatorTree &DT) {
+ if (isa<SCEVConstant>(S))
+ return 0;
+ if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+ if (const Instruction *I = dyn_cast<Instruction>(U->getValue()))
+ return LI.getLoopFor(I->getParent());
+ return 0;
+ }
+ if (const SCEVNAryExpr *N = dyn_cast<SCEVNAryExpr>(S)) {
+ const Loop *L = 0;
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
+ L = AR->getLoop();
+ for (SCEVNAryExpr::op_iterator I = N->op_begin(), E = N->op_end();
+ I != E; ++I)
+ L = PickMostRelevantLoop(L, GetRelevantLoop(*I, LI, DT), DT);
+ return L;
+ }
+ if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
+ return GetRelevantLoop(C->getOperand(), LI, DT);
+ if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S))
+ return PickMostRelevantLoop(GetRelevantLoop(D->getLHS(), LI, DT),
+ GetRelevantLoop(D->getRHS(), LI, DT),
+ DT);
+ llvm_unreachable("Unexpected SCEV type!");
+}
+
+/// LoopCompare - Compare loops by PickMostRelevantLoop.
+class LoopCompare {
+ DominatorTree &DT;
+public:
+ explicit LoopCompare(DominatorTree &dt) : DT(dt) {}
+
+ bool operator()(std::pair<const Loop *, const SCEV *> LHS,
+ std::pair<const Loop *, const SCEV *> RHS) const {
+ // Compare loops with PickMostRelevantLoop.
+ if (LHS.first != RHS.first)
+ return PickMostRelevantLoop(LHS.first, RHS.first, DT) != LHS.first;
+
+ // If one operand is a non-constant negative and the other is not,
+ // put the non-constant negative on the right so that a sub can
+ // be used instead of a negate and add.
+ if (isNonConstantNegative(LHS.second)) {
+ if (!isNonConstantNegative(RHS.second))
+ return false;
+ } else if (isNonConstantNegative(RHS.second))
+ return true;
+
+ // Otherwise they are equivalent according to this comparison.
+ return false;
+ }
+};
+
+Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
+ const Type *Ty = SE.getEffectiveSCEVType(S->getType());
+
+ // Collect all the add operands in a loop, along with their associated loops.
+ // Iterate in reverse so that constants are emitted last, all else equal, and
+ // so that pointer operands are inserted first, which the code below relies on
+ // to form more involved GEPs.
+ SmallVector<std::pair<const Loop *, const SCEV *>, 8> OpsAndLoops;
+ for (std::reverse_iterator<SCEVAddExpr::op_iterator> I(S->op_end()),
+ E(S->op_begin()); I != E; ++I)
+ OpsAndLoops.push_back(std::make_pair(GetRelevantLoop(*I, *SE.LI, *SE.DT),
+ *I));
+
+ // Sort by loop. Use a stable sort so that constants follow non-constants and
+ // pointer operands precede non-pointer operands.
+ std::stable_sort(OpsAndLoops.begin(), OpsAndLoops.end(), LoopCompare(*SE.DT));
+
+ // Emit instructions to add all the operands. Hoist as much as possible
+ // out of loops, and form meaningful getelementptrs where possible.
+ Value *Sum = 0;
+ for (SmallVectorImpl<std::pair<const Loop *, const SCEV *> >::iterator
+ I = OpsAndLoops.begin(), E = OpsAndLoops.end(); I != E; ) {
+ const Loop *CurLoop = I->first;
+ const SCEV *Op = I->second;
+ if (!Sum) {
+ // This is the first operand. Just expand it.
+ Sum = expand(Op);
+ ++I;
+ } else if (const PointerType *PTy = dyn_cast<PointerType>(Sum->getType())) {
+ // The running sum expression is a pointer. Try to form a getelementptr
+ // at this level with that as the base.
+ SmallVector<const SCEV *, 4> NewOps;
+ for (; I != E && I->first == CurLoop; ++I)
+ NewOps.push_back(I->second);
+ Sum = expandAddToGEP(NewOps.begin(), NewOps.end(), PTy, Ty, Sum);
+ } else if (const PointerType *PTy = dyn_cast<PointerType>(Op->getType())) {
+ // The running sum is an integer, and there's a pointer at this level.
+ // Try to form a getelementptr.
+ SmallVector<const SCEV *, 4> NewOps;
+ NewOps.push_back(SE.getUnknown(Sum));
+ for (++I; I != E && I->first == CurLoop; ++I)
+ NewOps.push_back(I->second);
+ Sum = expandAddToGEP(NewOps.begin(), NewOps.end(), PTy, Ty, expand(Op));
+ } else if (isNonConstantNegative(Op)) {
+ // Instead of doing a negate and add, just do a subtract.
+ Value *W = expandCodeFor(SE.getNegativeSCEV(Op), Ty);
+ Sum = InsertNoopCastOfTo(Sum, Ty);
+ Sum = InsertBinop(Instruction::Sub, Sum, W);
+ ++I;
+ } else {
+ // A simple add.
+ Value *W = expandCodeFor(Op, Ty);
+ Sum = InsertNoopCastOfTo(Sum, Ty);
+ // Canonicalize a constant to the RHS.
+ if (isa<Constant>(Sum)) std::swap(Sum, W);
+ Sum = InsertBinop(Instruction::Add, Sum, W);
+ ++I;
+ }
+ }