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//===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the classes used to generate code from scalar expressions.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Optional.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionNormalization.h"
#include "llvm/Analysis/TargetFolder.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/ValueHandle.h"
namespace llvm {
class TargetTransformInfo;
/// 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.
bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
/// 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,
ScalarEvolution &SE);
/// 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;
// InsertedExpressions caches Values for reuse, so must track RAUW.
DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
// InsertedValues only flags inserted instructions so needs no RAUW.
DenseSet<AssertingVH<Value>> InsertedValues;
DenseSet<AssertingVH<Value>> InsertedPostIncValues;
/// 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, expressions are expanded in "canonical" form. In particular,
/// addrecs are expanded as arithmetic based on a canonical induction
/// variable. When false, expression are expanded in a more literal form.
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<TargetFolder> 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;
SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
: Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
~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);
Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
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;
#ifndef NDEBUG
const char *DebugType;
friend struct SCEVVisitor<SCEVExpander, Value*>;
/// Construct a SCEVExpander in "canonical" mode.
explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
const char *name)
: SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr),
IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false),
Builder(se.getContext(), TargetFolder(DL)) {
#ifndef NDEBUG
DebugType = "";
~SCEVExpander() {
// Make sure the insert point guard stack is consistent.
#ifndef NDEBUG
void setDebugType(const char* s) { DebugType = s; }
/// 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() {
/// Return true for expressions that may incur non-trivial cost to evaluate
/// at runtime.
/// At is an optional parameter which specifies point in code where user is
/// going to expand this expression. Sometimes this knowledge can lead to a
/// more accurate cost estimation.
bool isHighCostExpansion(const SCEV *Expr, Loop *L,
const Instruction *At = nullptr) {
SmallPtrSet<const SCEV *, 8> Processed;
return isHighCostExpansionHelper(Expr, L, At, Processed);
/// This method returns the canonical induction variable of the specified
/// type for the specified loop (inserting one if there is none). A
/// canonical induction variable starts at zero and steps by one on each
/// iteration.
PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
/// Return the induction variable increment's IV operand.
Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
bool allowScale);
/// Utility for hoisting an IV increment.
bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
/// 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);
/// Insert code to directly compute the specified SCEV expression into the
/// program. The inserted code is inserted into the specified block.
Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
/// Insert code to directly compute the specified SCEV expression into the
/// program. The inserted 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);
/// 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 SCEVEqualPredicate.
Value *expandEqualPredicate(const SCEVEqualPredicate *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() {
// When we change the post-inc loop set, cached expansions may no
// longer be valid.
/// 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) {
/// 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() {
/// Return true if the specified instruction was inserted by the code
/// rewriter. If so, the client should not modify the instruction.
bool isInsertedInstruction(Instruction *I) const {
return InsertedValues.count(I) || InsertedPostIncValues.count(I);
void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
/// Try to find existing LLVM IR value for S available at the point At.
Value *getExactExistingExpansion(const SCEV *S, const Instruction *At,
Loop *L);
/// 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.
getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L);
LLVMContext &getContext() const { return SE.getContext(); }
/// Recursive helper function for isHighCostExpansion.
bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
const Instruction *At,
SmallPtrSetImpl<const SCEV *> &Processed);
/// Insert the specified binary operator, doing a small amount of work to
/// avoid inserting an obviously redundant operation.
Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
/// 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.
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 *visitConstant(const SCEVConstant *S) {
return S->getValue();
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 *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 hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist,
Instruction *Pos, PHINode *LoopPhi);
void fixupInsertPoints(Instruction *I);