//===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the classes used to generate code from scalar expressions.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_UTILS_SCALAREVOLUTIONEXPANDER_H
#define LLVM_TRANSFORMS_UTILS_SCALAREVOLUTIONEXPANDER_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/InstSimplifyFolder.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionNormalization.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/InstructionCost.h"
namespace llvm {
extern cl::opt<unsigned> SCEVCheapExpansionBudget;
/// struct for holding enough information to help calculate the cost of the
/// given SCEV when expanded into IR.
struct SCEVOperand {
explicit SCEVOperand(unsigned Opc, int Idx, const SCEV *S) :
ParentOpcode(Opc), OperandIdx(Idx), S(S) { }
/// LLVM instruction opcode that uses the operand.
unsigned ParentOpcode;
/// The use index of an expanded instruction.
int OperandIdx;
/// The SCEV operand to be costed.
const SCEV* S;
};
/// This class uses information about analyze scalars to rewrite expressions
/// in canonical form.
///
/// Clients should create an instance of this class when rewriting is needed,
/// and destroy it when finished to allow the release of the associated
/// memory.
class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
ScalarEvolution &SE;
const DataLayout &DL;
// New instructions receive a name to identify them with the current pass.
const char *IVName;
/// Indicates whether LCSSA phis should be created for inserted values.
bool PreserveLCSSA;
// InsertedExpressions caches Values for reuse, so must track RAUW.
DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
InsertedExpressions;
// InsertedValues only flags inserted instructions so needs no RAUW.
DenseSet<AssertingVH<Value>> InsertedValues;
DenseSet<AssertingVH<Value>> InsertedPostIncValues;
/// Keep track of the existing IR values re-used during expansion.
/// FIXME: Ideally re-used instructions would not be added to
/// InsertedValues/InsertedPostIncValues.
SmallPtrSet<Value *, 16> ReusedValues;
// The induction variables generated.
SmallVector<WeakVH, 2> InsertedIVs;
/// A memoization of the "relevant" loop for a given SCEV.
DenseMap<const SCEV *, const Loop *> RelevantLoops;
/// Addrecs referring to any of the given loops are expanded in post-inc
/// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
/// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
/// phi starting at 1. This is only supported in non-canonical mode.
PostIncLoopSet PostIncLoops;
/// When this is non-null, addrecs expanded in the loop it indicates should
/// be inserted with increments at IVIncInsertPos.
const Loop *IVIncInsertLoop;
/// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
/// increment at this position.
Instruction *IVIncInsertPos;
/// Phis that complete an IV chain. Reuse
DenseSet<AssertingVH<PHINode>> ChainedPhis;
/// When true, SCEVExpander tries to expand expressions in "canonical" form.
/// When false, expressions are expanded in a more literal form.
///
/// In "canonical" form addrecs are expanded as arithmetic based on a
/// canonical induction variable. Note that CanonicalMode doesn't guarantee
/// that all expressions are expanded in "canonical" form. For some
/// expressions literal mode can be preferred.
bool CanonicalMode;
/// When invoked from LSR, the expander is in "strength reduction" mode. The
/// only difference is that phi's are only reused if they are already in
/// "expanded" form.
bool LSRMode;
typedef IRBuilder<InstSimplifyFolder, IRBuilderCallbackInserter> BuilderType;
BuilderType Builder;
// RAII object that stores the current insertion point and restores it when
// the object is destroyed. This includes the debug location. Duplicated
// from InsertPointGuard to add SetInsertPoint() which is used to updated
// InsertPointGuards stack when insert points are moved during SCEV
// expansion.
class SCEVInsertPointGuard {
IRBuilderBase &Builder;
AssertingVH<BasicBlock> Block;
BasicBlock::iterator Point;
DebugLoc DbgLoc;
SCEVExpander *SE;
SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
public:
SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
: Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
SE->InsertPointGuards.push_back(this);
}
~SCEVInsertPointGuard() {
// These guards should always created/destroyed in FIFO order since they
// are used to guard lexically scoped blocks of code in
// ScalarEvolutionExpander.
assert(SE->InsertPointGuards.back() == this);
SE->InsertPointGuards.pop_back();
Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
Builder.SetCurrentDebugLocation(DbgLoc);
}
BasicBlock::iterator GetInsertPoint() const { return Point; }
void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
};
/// Stack of pointers to saved insert points, used to keep insert points
/// consistent when instructions are moved.
SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS
const char *DebugType;
#endif
friend struct SCEVVisitor<SCEVExpander, Value *>;
public:
/// Construct a SCEVExpander in "canonical" mode.
explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
const char *name, bool PreserveLCSSA = true)
: SE(se), DL(DL), IVName(name), PreserveLCSSA(PreserveLCSSA),
IVIncInsertLoop(nullptr), IVIncInsertPos(nullptr), CanonicalMode(true),
LSRMode(false),
Builder(se.getContext(), InstSimplifyFolder(DL),
IRBuilderCallbackInserter(
[this](Instruction *I) { rememberInstruction(I); })) {
#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS
DebugType = "";
#endif
}
~SCEVExpander() {
// Make sure the insert point guard stack is consistent.
assert(InsertPointGuards.empty());
}
#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS
void setDebugType(const char *s) { DebugType = s; }
#endif
/// Erase the contents of the InsertedExpressions map so that users trying
/// to expand the same expression into multiple BasicBlocks or different
/// places within the same BasicBlock can do so.
void clear() {
InsertedExpressions.clear();
InsertedValues.clear();
InsertedPostIncValues.clear();
ReusedValues.clear();
ChainedPhis.clear();
InsertedIVs.clear();
}
ScalarEvolution *getSE() { return &SE; }
const SmallVectorImpl<WeakVH> &getInsertedIVs() const { return InsertedIVs; }
/// Return a vector containing all instructions inserted during expansion.
SmallVector<Instruction *, 32> getAllInsertedInstructions() const {
SmallVector<Instruction *, 32> Result;
for (const auto &VH : InsertedValues) {
Value *V = VH;
if (ReusedValues.contains(V))
continue;
if (auto *Inst = dyn_cast<Instruction>(V))
Result.push_back(Inst);
}
for (const auto &VH : InsertedPostIncValues) {
Value *V = VH;
if (ReusedValues.contains(V))
continue;
if (auto *Inst = dyn_cast<Instruction>(V))
Result.push_back(Inst);
}
return Result;
}
/// Return true for expressions that can't be evaluated at runtime
/// within given \b Budget.
///
/// \p At is a parameter which specifies point in code where user is going to
/// expand these expressions. Sometimes this knowledge can lead to
/// a less pessimistic cost estimation.
bool isHighCostExpansion(ArrayRef<const SCEV *> Exprs, Loop *L,
unsigned Budget, const TargetTransformInfo *TTI,
const Instruction *At) {
assert(TTI && "This function requires TTI to be provided.");
assert(At && "This function requires At instruction to be provided.");
if (!TTI) // In assert-less builds, avoid crashing
return true; // by always claiming to be high-cost.
SmallVector<SCEVOperand, 8> Worklist;
SmallPtrSet<const SCEV *, 8> Processed;
InstructionCost Cost = 0;
unsigned ScaledBudget = Budget * TargetTransformInfo::TCC_Basic;
for (auto *Expr : Exprs)
Worklist.emplace_back(-1, -1, Expr);
while (!Worklist.empty()) {
const SCEVOperand WorkItem = Worklist.pop_back_val();
if (isHighCostExpansionHelper(WorkItem, L, *At, Cost, ScaledBudget, *TTI,
Processed, Worklist))
return true;
}
assert(Cost <= ScaledBudget && "Should have returned from inner loop.");
return false;
}
/// Return the induction variable increment's IV operand.
Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
bool allowScale);
/// Utility for hoisting \p IncV (with all subexpressions requried for its
/// computation) before \p InsertPos. If \p RecomputePoisonFlags is set, drops
/// all poison-generating flags from instructions being hoisted and tries to
/// re-infer them in the new location. It should be used when we are going to
/// introduce a new use in the new position that didn't exist before, and may
/// trigger new UB in case of poison.
bool hoistIVInc(Instruction *IncV, Instruction *InsertPos,
bool RecomputePoisonFlags = false);
/// replace congruent phis with their most canonical representative. Return
/// the number of phis eliminated.
unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
SmallVectorImpl<WeakTrackingVH> &DeadInsts,
const TargetTransformInfo *TTI = nullptr);
/// Return true if the given expression is safe to expand in the sense that
/// all materialized values are safe to speculate anywhere their operands are
/// defined, and the expander is capable of expanding the expression.
bool isSafeToExpand(const SCEV *S) const;
/// Return true if the given expression is safe to expand in the sense that
/// all materialized values are defined and safe to speculate at the specified
/// location and their operands are defined at this location.
bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint) const;
/// Insert code to directly compute the specified SCEV expression into the
/// program. The code is inserted into the specified block.
Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I) {
return expandCodeForImpl(SH, Ty, I);
}
/// Insert code to directly compute the specified SCEV expression into the
/// program. The code is inserted into the SCEVExpander's current
/// insertion point. If a type is specified, the result will be expanded to
/// have that type, with a cast if necessary.
Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr) {
return expandCodeForImpl(SH, Ty);
}
/// Generates a code sequence that evaluates this predicate. The inserted
/// instructions will be at position \p Loc. The result will be of type i1
/// and will have a value of 0 when the predicate is false and 1 otherwise.
Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
/// A specialized variant of expandCodeForPredicate, handling the case when
/// we are expanding code for a SCEVComparePredicate.
Value *expandComparePredicate(const SCEVComparePredicate *Pred,
Instruction *Loc);
/// Generates code that evaluates if the \p AR expression will overflow.
Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
bool Signed);
/// A specialized variant of expandCodeForPredicate, handling the case when
/// we are expanding code for a SCEVWrapPredicate.
Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
/// A specialized variant of expandCodeForPredicate, handling the case when
/// we are expanding code for a SCEVUnionPredicate.
Value *expandUnionPredicate(const SCEVUnionPredicate *Pred, Instruction *Loc);
/// Set the current IV increment loop and position.
void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
assert(!CanonicalMode &&
"IV increment positions are not supported in CanonicalMode");
IVIncInsertLoop = L;
IVIncInsertPos = Pos;
}
/// Enable post-inc expansion for addrecs referring to the given
/// loops. Post-inc expansion is only supported in non-canonical mode.
void setPostInc(const PostIncLoopSet &L) {
assert(!CanonicalMode &&
"Post-inc expansion is not supported in CanonicalMode");
PostIncLoops = L;
}
/// Disable all post-inc expansion.
void clearPostInc() {
PostIncLoops.clear();
// When we change the post-inc loop set, cached expansions may no
// longer be valid.
InsertedPostIncValues.clear();
}
/// Disable the behavior of expanding expressions in canonical form rather
/// than in a more literal form. Non-canonical mode is useful for late
/// optimization passes.
void disableCanonicalMode() { CanonicalMode = false; }
void enableLSRMode() { LSRMode = true; }
/// Set the current insertion point. This is useful if multiple calls to
/// expandCodeFor() are going to be made with the same insert point and the
/// insert point may be moved during one of the expansions (e.g. if the
/// insert point is not a block terminator).
void setInsertPoint(Instruction *IP) {
assert(IP);
Builder.SetInsertPoint(IP);
}
/// Clear the current insertion point. This is useful if the instruction
/// that had been serving as the insertion point may have been deleted.
void clearInsertPoint() { Builder.ClearInsertionPoint(); }
/// Set location information used by debugging information.
void SetCurrentDebugLocation(DebugLoc L) {
Builder.SetCurrentDebugLocation(std::move(L));
}
/// Get location information used by debugging information.
DebugLoc getCurrentDebugLocation() const {
return Builder.getCurrentDebugLocation();
}
/// Return true if the specified instruction was inserted by the code
/// rewriter. If so, the client should not modify the instruction. Note that
/// this also includes instructions re-used during expansion.
bool isInsertedInstruction(Instruction *I) const {
return InsertedValues.count(I) || InsertedPostIncValues.count(I);
}
void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
/// Try to find the ValueOffsetPair for S. The function is mainly used to
/// check whether S can be expanded cheaply. If this returns a non-None
/// value, we know we can codegen the `ValueOffsetPair` into a suitable
/// expansion identical with S so that S can be expanded cheaply.
///
/// L is a hint which tells in which loop to look for the suitable value.
/// On success return value which is equivalent to the expanded S at point
/// At. Return nullptr if value was not found.
///
/// Note that this function does not perform an exhaustive search. I.e if it
/// didn't find any value it does not mean that there is no such value.
///
Value *getRelatedExistingExpansion(const SCEV *S, const Instruction *At,
Loop *L);
/// Returns a suitable insert point after \p I, that dominates \p
/// MustDominate. Skips instructions inserted by the expander.
BasicBlock::iterator findInsertPointAfter(Instruction *I,
Instruction *MustDominate) const;
private:
LLVMContext &getContext() const { return SE.getContext(); }
/// Insert code to directly compute the specified SCEV expression into the
/// program. The code is inserted into the SCEVExpander's current
/// insertion point. If a type is specified, the result will be expanded to
/// have that type, with a cast if necessary. If \p Root is true, this
/// indicates that \p SH is the top-level expression to expand passed from
/// an external client call.
Value *expandCodeForImpl(const SCEV *SH, Type *Ty);
/// Insert code to directly compute the specified SCEV expression into the
/// program. The code is inserted into the specified block. If \p
/// Root is true, this indicates that \p SH is the top-level expression to
/// expand passed from an external client call.
Value *expandCodeForImpl(const SCEV *SH, Type *Ty, Instruction *I);
/// Recursive helper function for isHighCostExpansion.
bool isHighCostExpansionHelper(const SCEVOperand &WorkItem, Loop *L,
const Instruction &At, InstructionCost &Cost,
unsigned Budget,
const TargetTransformInfo &TTI,
SmallPtrSetImpl<const SCEV *> &Processed,
SmallVectorImpl<SCEVOperand> &Worklist);
/// Insert the specified binary operator, doing a small amount of work to
/// avoid inserting an obviously redundant operation, and hoisting to an
/// outer loop when the opportunity is there and it is safe.
Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS,
SCEV::NoWrapFlags Flags, bool IsSafeToHoist);
/// We want to cast \p V. What would be the best place for such a cast?
BasicBlock::iterator GetOptimalInsertionPointForCastOf(Value *V) const;
/// Arrange for there to be a cast of V to Ty at IP, reusing an existing
/// cast if a suitable one exists, moving an existing cast if a suitable one
/// exists but isn't in the right place, or creating a new one.
Value *ReuseOrCreateCast(Value *V, Type *Ty, Instruction::CastOps Op,
BasicBlock::iterator IP);
/// Insert a cast of V to the specified type, which must be possible with a
/// noop cast, doing what we can to share the casts.
Value *InsertNoopCastOfTo(Value *V, Type *Ty);
/// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
/// ptrtoint+arithmetic+inttoptr.
Value *expandAddToGEP(const SCEV *const *op_begin, const SCEV *const *op_end,
PointerType *PTy, Type *Ty, Value *V);
Value *expandAddToGEP(const SCEV *Op, PointerType *PTy, Type *Ty, Value *V);
/// Find a previous Value in ExprValueMap for expand.
Value *FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt);
Value *expand(const SCEV *S);
/// Determine the most "relevant" loop for the given SCEV.
const Loop *getRelevantLoop(const SCEV *);
Value *expandMinMaxExpr(const SCEVNAryExpr *S, Intrinsic::ID IntrinID,
Twine Name, bool IsSequential = false);
Value *visitConstant(const SCEVConstant *S) { return S->getValue(); }
Value *visitPtrToIntExpr(const SCEVPtrToIntExpr *S);
Value *visitTruncateExpr(const SCEVTruncateExpr *S);
Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
Value *visitAddExpr(const SCEVAddExpr *S);
Value *visitMulExpr(const SCEVMulExpr *S);
Value *visitUDivExpr(const SCEVUDivExpr *S);
Value *visitAddRecExpr(const SCEVAddRecExpr *S);
Value *visitSMaxExpr(const SCEVSMaxExpr *S);
Value *visitUMaxExpr(const SCEVUMaxExpr *S);
Value *visitSMinExpr(const SCEVSMinExpr *S);
Value *visitUMinExpr(const SCEVUMinExpr *S);
Value *visitSequentialUMinExpr(const SCEVSequentialUMinExpr *S);
Value *visitUnknown(const SCEVUnknown *S) { return S->getValue(); }
void rememberInstruction(Value *I);
bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
const Loop *L, Type *ExpandTy, Type *IntTy,
Type *&TruncTy, bool &InvertStep);
Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L, Type *ExpandTy,
Type *IntTy, bool useSubtract);
void fixupInsertPoints(Instruction *I);
/// Create LCSSA PHIs for \p V, if it is required for uses at the Builder's
/// current insertion point.
Value *fixupLCSSAFormFor(Value *V);
};
/// Helper to remove instructions inserted during SCEV expansion, unless they
/// are marked as used.
class SCEVExpanderCleaner {
SCEVExpander &Expander;
/// Indicates whether the result of the expansion is used. If false, the
/// instructions added during expansion are removed.
bool ResultUsed;
public:
SCEVExpanderCleaner(SCEVExpander &Expander)
: Expander(Expander), ResultUsed(false) {}
~SCEVExpanderCleaner() { cleanup(); }
/// Indicate that the result of the expansion is used.
void markResultUsed() { ResultUsed = true; }
void cleanup();
};
} // namespace llvm
#endif