bool InductionDescriptor::isInductionPHI(PHINode *Phi, const Loop *TheLoop,
PredicatedScalarEvolution &PSE,
InductionDescriptor &D,
bool Assume) {
Type *PhiTy = Phi->getType();
// Handle integer and pointer inductions variables.
// Now we handle also FP induction but not trying to make a
// recurrent expression from the PHI node in-place.
if (!PhiTy->isIntegerTy() && !PhiTy->isPointerTy() &&
!PhiTy->isFloatTy() && !PhiTy->isDoubleTy() && !PhiTy->isHalfTy())
return false;
if (PhiTy->isFloatingPointTy())
return isFPInductionPHI(Phi, TheLoop, PSE.getSE(), D);
const SCEV *PhiScev = PSE.getSCEV(Phi);
const auto *AR = dyn_cast<SCEVAddRecExpr>(PhiScev);
// We need this expression to be an AddRecExpr.
if (Assume && !AR)
AR = PSE.getAsAddRec(Phi);
if (!AR) {
DEBUG(dbgs() << "LV: PHI is not a poly recurrence.\n");
return false;
}
return isInductionPHI(Phi, TheLoop, PSE.getSE(), D, AR);
}
bool InductionDescriptor::isInductionPHI(PHINode *Phi, const Loop *TheLoop,
PredicatedScalarEvolution &PSE,
InductionDescriptor &D, bool Assume) {
Type *PhiTy = Phi->getType();
// Handle integer and pointer inductions variables.
// Now we handle also FP induction but not trying to make a
// recurrent expression from the PHI node in-place.
if (!PhiTy->isIntegerTy() && !PhiTy->isPointerTy() && !PhiTy->isFloatTy() &&
!PhiTy->isDoubleTy() && !PhiTy->isHalfTy())
return false;
if (PhiTy->isFloatingPointTy())
return isFPInductionPHI(Phi, TheLoop, PSE.getSE(), D);
const SCEV *PhiScev = PSE.getSCEV(Phi);
const auto *AR = dyn_cast<SCEVAddRecExpr>(PhiScev);
// We need this expression to be an AddRecExpr.
if (Assume && !AR)
AR = PSE.getAsAddRec(Phi);
if (!AR) {
LLVM_DEBUG(dbgs() << "LV: PHI is not a poly recurrence.\n");
return false;
}
// Record any Cast instructions that participate in the induction update
const auto *SymbolicPhi = dyn_cast<SCEVUnknown>(PhiScev);
// If we started from an UnknownSCEV, and managed to build an addRecurrence
// only after enabling Assume with PSCEV, this means we may have encountered
// cast instructions that required adding a runtime check in order to
// guarantee the correctness of the AddRecurrence respresentation of the
// induction.
if (PhiScev != AR && SymbolicPhi) {
SmallVector<Instruction *, 2> Casts;
if (getCastsForInductionPHI(PSE, SymbolicPhi, AR, Casts))
return isInductionPHI(Phi, TheLoop, PSE.getSE(), D, AR, &Casts);
}
return isInductionPHI(Phi, TheLoop, PSE.getSE(), D, AR);
}
bool InductionDescriptor::isInductionPHI(PHINode *Phi,
PredicatedScalarEvolution &PSE,
InductionDescriptor &D,
bool Assume) {
Type *PhiTy = Phi->getType();
// We only handle integer and pointer inductions variables.
if (!PhiTy->isIntegerTy() && !PhiTy->isPointerTy())
return false;
const SCEV *PhiScev = PSE.getSCEV(Phi);
const auto *AR = dyn_cast<SCEVAddRecExpr>(PhiScev);
// We need this expression to be an AddRecExpr.
if (Assume && !AR)
AR = PSE.getAsAddRec(Phi);
if (!AR) {
DEBUG(dbgs() << "LV: PHI is not a poly recurrence.\n");
return false;
}
return isInductionPHI(Phi, PSE.getSE(), D, AR);
}
/// This function is called when we suspect that the update-chain of a phi node
/// (whose symbolic SCEV expression sin \p PhiScev) contains redundant casts,
/// that can be ignored. (This can happen when the PSCEV rewriter adds a runtime
/// predicate P under which the SCEV expression for the phi can be the
/// AddRecurrence \p AR; See createAddRecFromPHIWithCast). We want to find the
/// cast instructions that are involved in the update-chain of this induction.
/// A caller that adds the required runtime predicate can be free to drop these
/// cast instructions, and compute the phi using \p AR (instead of some scev
/// expression with casts).
///
/// For example, without a predicate the scev expression can take the following
/// form:
/// (Ext ix (Trunc iy ( Start + i*Step ) to ix) to iy)
///
/// It corresponds to the following IR sequence:
/// %for.body:
/// %x = phi i64 [ 0, %ph ], [ %add, %for.body ]
/// %casted_phi = "ExtTrunc i64 %x"
/// %add = add i64 %casted_phi, %step
///
/// where %x is given in \p PN,
/// PSE.getSCEV(%x) is equal to PSE.getSCEV(%casted_phi) under a predicate,
/// and the IR sequence that "ExtTrunc i64 %x" represents can take one of
/// several forms, for example, such as:
/// ExtTrunc1: %casted_phi = and %x, 2^n-1
/// or:
/// ExtTrunc2: %t = shl %x, m
/// %casted_phi = ashr %t, m
///
/// If we are able to find such sequence, we return the instructions
/// we found, namely %casted_phi and the instructions on its use-def chain up
/// to the phi (not including the phi).
static bool getCastsForInductionPHI(PredicatedScalarEvolution &PSE,
const SCEVUnknown *PhiScev,
const SCEVAddRecExpr *AR,
SmallVectorImpl<Instruction *> &CastInsts) {
assert(CastInsts.empty() && "CastInsts is expected to be empty.");
auto *PN = cast<PHINode>(PhiScev->getValue());
assert(PSE.getSCEV(PN) == AR && "Unexpected phi node SCEV expression");
const Loop *L = AR->getLoop();
// Find any cast instructions that participate in the def-use chain of
// PhiScev in the loop.
// FORNOW/TODO: We currently expect the def-use chain to include only
// two-operand instructions, where one of the operands is an invariant.
// createAddRecFromPHIWithCasts() currently does not support anything more
// involved than that, so we keep the search simple. This can be
// extended/generalized as needed.
auto getDef = [&](const Value *Val) -> Value * {
const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Val);
if (!BinOp)
return nullptr;
Value *Op0 = BinOp->getOperand(0);
Value *Op1 = BinOp->getOperand(1);
Value *Def = nullptr;
if (L->isLoopInvariant(Op0))
Def = Op1;
else if (L->isLoopInvariant(Op1))
Def = Op0;
return Def;
};
// Look for the instruction that defines the induction via the
// loop backedge.
BasicBlock *Latch = L->getLoopLatch();
if (!Latch)
return false;
Value *Val = PN->getIncomingValueForBlock(Latch);
if (!Val)
return false;
// Follow the def-use chain until the induction phi is reached.
// If on the way we encounter a Value that has the same SCEV Expr as the
// phi node, we can consider the instructions we visit from that point
// as part of the cast-sequence that can be ignored.
bool InCastSequence = false;
auto *Inst = dyn_cast<Instruction>(Val);
while (Val != PN) {
// If we encountered a phi node other than PN, or if we left the loop,
// we bail out.
if (!Inst || !L->contains(Inst)) {
return false;
}
auto *AddRec = dyn_cast<SCEVAddRecExpr>(PSE.getSCEV(Val));
if (AddRec && PSE.areAddRecsEqualWithPreds(AddRec, AR))
InCastSequence = true;
if (InCastSequence) {
// Only the last instruction in the cast sequence is expected to have
// uses outside the induction def-use chain.
if (!CastInsts.empty())
if (!Inst->hasOneUse())
return false;
CastInsts.push_back(Inst);
}
Val = getDef(Val);
if (!Val)
return false;
Inst = dyn_cast<Instruction>(Val);
}
return InCastSequence;
}
