InstructionSimplify.h

Go to the documentation of this file.

//===-- InstructionSimplify.h - Fold instrs into simpler forms --*- 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 declares routines for folding instructions into simpler forms
// that do not require creating new instructions.  This does constant folding
// ("add i32 1, 1" -> "2") but can also handle non-constant operands, either
// returning a constant ("and i32 %x, 0" -> "0") or an already existing value
// ("and i32 %x, %x" -> "%x").  If the simplification is also an instruction
// then it dominates the original instruction.
//
// These routines implicitly resolve undef uses. The easiest way to be safe when
// using these routines to obtain simplified values for existing instructions is
// to always replace all uses of the instructions with the resulting simplified
// values. This will prevent other code from seeing the same undef uses and
// resolving them to different values.
//
// These routines are designed to tolerate moderately incomplete IR, such as
// instructions that are not connected to basic blocks yet. However, they do
// require that all the IR that they encounter be valid. In particular, they
// require that all non-constant values be defined in the same function, and the
// same call context of that function (and not split between caller and callee
// contexts of a directly recursive call, for example).
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_INSTRUCTIONSIMPLIFY_H
#define LLVM_ANALYSIS_INSTRUCTIONSIMPLIFY_H

#include "llvm/IR/Instruction.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/User.h"

namespace llvm {
class Function;
template <typename T, typename... TArgs> class AnalysisManager;
template <class T> class ArrayRef;
class AssumptionCache;
class CallBase;
class DominatorTree;
class DataLayout;
class FastMathFlags;
struct LoopStandardAnalysisResults;
class OptimizationRemarkEmitter;
class Pass;
class TargetLibraryInfo;
class Type;
class Value;
class MDNode;
class BinaryOperator;

/// InstrInfoQuery provides an interface to query additional information for
/// instructions like metadata or keywords like nsw, which provides conservative
/// results if the users specified it is safe to use.
struct InstrInfoQuery {
  InstrInfoQuery(bool UMD) : UseInstrInfo(UMD) {}
  InstrInfoQuery() : UseInstrInfo(true) {}
  bool UseInstrInfo = true;

  MDNode *getMetadata(const Instruction *I, unsigned KindID) const {
    if (UseInstrInfo)
      return I->getMetadata(KindID);
    return nullptr;
  }

  template <class InstT> bool hasNoUnsignedWrap(const InstT *Op) const {
    if (UseInstrInfo)
      return Op->hasNoUnsignedWrap();
    return false;
  }

  template <class InstT> bool hasNoSignedWrap(const InstT *Op) const {
    if (UseInstrInfo)
      return Op->hasNoSignedWrap();
    return false;
  }

  bool isExact(const BinaryOperator *Op) const {
    if (UseInstrInfo && isa<PossiblyExactOperator>(Op))
      return cast<PossiblyExactOperator>(Op)->isExact();
    return false;
  }
};

struct SimplifyQuery {
  const DataLayout &DL;
  const TargetLibraryInfo *TLI = nullptr;
  const DominatorTree *DT = nullptr;
  AssumptionCache *AC = nullptr;
  const Instruction *CxtI = nullptr;

  // Wrapper to query additional information for instructions like metadata or
  // keywords like nsw, which provides conservative results if those cannot
  // be safely used.
  const InstrInfoQuery IIQ;

  SimplifyQuery(const DataLayout &DL, const Instruction *CXTI = nullptr)
      : DL(DL), CxtI(CXTI) {}

  SimplifyQuery(const DataLayout &DL, const TargetLibraryInfo *TLI,
                const DominatorTree *DT = nullptr,
                AssumptionCache *AC = nullptr,
                const Instruction *CXTI = nullptr, bool UseInstrInfo = true)
      : DL(DL), TLI(TLI), DT(DT), AC(AC), CxtI(CXTI), IIQ(UseInstrInfo) {}
  SimplifyQuery getWithInstruction(Instruction *I) const {
    SimplifyQuery Copy(*this);
    Copy.CxtI = I;
    return Copy;
  }
};

// NOTE: the explicit multiple argument versions of these functions are
// deprecated.
// Please use the SimplifyQuery versions in new code.

/// Given operand for an FNeg, fold the result or return null.
Value *SimplifyFNegInst(Value *Op, FastMathFlags FMF,
                        const SimplifyQuery &Q);

/// Given operands for an Add, fold the result or return null.
Value *SimplifyAddInst(Value *LHS, Value *RHS, bool isNSW, bool isNUW,
                       const SimplifyQuery &Q);

/// Given operands for a Sub, fold the result or return null.
Value *SimplifySubInst(Value *LHS, Value *RHS, bool isNSW, bool isNUW,
                       const SimplifyQuery &Q);

/// Given operands for an FAdd, fold the result or return null.
Value *SimplifyFAddInst(Value *LHS, Value *RHS, FastMathFlags FMF,
                        const SimplifyQuery &Q);

/// Given operands for an FSub, fold the result or return null.
Value *SimplifyFSubInst(Value *LHS, Value *RHS, FastMathFlags FMF,
                        const SimplifyQuery &Q);

/// Given operands for an FMul, fold the result or return null.
Value *SimplifyFMulInst(Value *LHS, Value *RHS, FastMathFlags FMF,
                        const SimplifyQuery &Q);

/// Given operands for a Mul, fold the result or return null.
Value *SimplifyMulInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for an SDiv, fold the result or return null.
Value *SimplifySDivInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for a UDiv, fold the result or return null.
Value *SimplifyUDivInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for an FDiv, fold the result or return null.
Value *SimplifyFDivInst(Value *LHS, Value *RHS, FastMathFlags FMF,
                        const SimplifyQuery &Q);

/// Given operands for an SRem, fold the result or return null.
Value *SimplifySRemInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for a URem, fold the result or return null.
Value *SimplifyURemInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for an FRem, fold the result or return null.
Value *SimplifyFRemInst(Value *LHS, Value *RHS, FastMathFlags FMF,
                        const SimplifyQuery &Q);

/// Given operands for a Shl, fold the result or return null.
Value *SimplifyShlInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
                       const SimplifyQuery &Q);

/// Given operands for a LShr, fold the result or return null.
Value *SimplifyLShrInst(Value *Op0, Value *Op1, bool isExact,
                        const SimplifyQuery &Q);

/// Given operands for a AShr, fold the result or return nulll.
Value *SimplifyAShrInst(Value *Op0, Value *Op1, bool isExact,
                        const SimplifyQuery &Q);

/// Given operands for an And, fold the result or return null.
Value *SimplifyAndInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for an Or, fold the result or return null.
Value *SimplifyOrInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for an Xor, fold the result or return null.
Value *SimplifyXorInst(Value *LHS, Value *RHS, const SimplifyQuery &Q);

/// Given operands for an ICmpInst, fold the result or return null.
Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
                        const SimplifyQuery &Q);

/// Given operands for an FCmpInst, fold the result or return null.
Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
                        FastMathFlags FMF, const SimplifyQuery &Q);

/// Given operands for a SelectInst, fold the result or return null.
Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
                          const SimplifyQuery &Q);

/// Given operands for a GetElementPtrInst, fold the result or return null.
Value *SimplifyGEPInst(Type *SrcTy, ArrayRef<Value *> Ops,
                       const SimplifyQuery &Q);

/// Given operands for an InsertValueInst, fold the result or return null.
Value *SimplifyInsertValueInst(Value *Agg, Value *Val, ArrayRef<unsigned> Idxs,
                               const SimplifyQuery &Q);

/// Given operands for an InsertElement, fold the result or return null.
Value *SimplifyInsertElementInst(Value *Vec, Value *Elt, Value *Idx,
                                 const SimplifyQuery &Q);

/// Given operands for an ExtractValueInst, fold the result or return null.
Value *SimplifyExtractValueInst(Value *Agg, ArrayRef<unsigned> Idxs,
                                const SimplifyQuery &Q);

/// Given operands for an ExtractElementInst, fold the result or return null.
Value *SimplifyExtractElementInst(Value *Vec, Value *Idx,
                                  const SimplifyQuery &Q);

/// Given operands for a CastInst, fold the result or return null.
Value *SimplifyCastInst(unsigned CastOpc, Value *Op, Type *Ty,
                        const SimplifyQuery &Q);

/// Given operands for a ShuffleVectorInst, fold the result or return null.
Value *SimplifyShuffleVectorInst(Value *Op0, Value *Op1, Constant *Mask,
                                 Type *RetTy, const SimplifyQuery &Q);

//=== Helper functions for higher up the class hierarchy.

/// Given operands for a CmpInst, fold the result or return null.
Value *SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
                       const SimplifyQuery &Q);

/// Given operand for a UnaryOperator, fold the result or return null.
Value *SimplifyUnOp(unsigned Opcode, Value *Op, const SimplifyQuery &Q);

/// Given operand for an FP UnaryOperator, fold the result or return null.
/// In contrast to SimplifyUnOp, try to use FastMathFlag when folding the
/// result. In case we don't need FastMathFlags, simply fall to SimplifyUnOp.
Value *SimplifyFPUnOp(unsigned Opcode, Value *Op, FastMathFlags FMF,
                      const SimplifyQuery &Q);

/// Given operands for a BinaryOperator, fold the result or return null.
Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
                     const SimplifyQuery &Q);

/// Given operands for an FP BinaryOperator, fold the result or return null.
/// In contrast to SimplifyBinOp, try to use FastMathFlag when folding the
/// result. In case we don't need FastMathFlags, simply fall to SimplifyBinOp.
Value *SimplifyFPBinOp(unsigned Opcode, Value *LHS, Value *RHS,
                       FastMathFlags FMF, const SimplifyQuery &Q);

/// Given a callsite, fold the result or return null.
Value *SimplifyCall(CallBase *Call, const SimplifyQuery &Q);

/// See if we can compute a simplified version of this instruction. If not,
/// return null.
Value *SimplifyInstruction(Instruction *I, const SimplifyQuery &Q,
                           OptimizationRemarkEmitter *ORE = nullptr);

/// Replace all uses of 'I' with 'SimpleV' and simplify the uses recursively.
///
/// This first performs a normal RAUW of I with SimpleV. It then recursively
/// attempts to simplify those users updated by the operation. The 'I'
/// instruction must not be equal to the simplified value 'SimpleV'.
///
/// The function returns true if any simplifications were performed.
bool replaceAndRecursivelySimplify(Instruction *I, Value *SimpleV,
                                   const TargetLibraryInfo *TLI = nullptr,
                                   const DominatorTree *DT = nullptr,
                                   AssumptionCache *AC = nullptr);

/// Recursively attempt to simplify an instruction.
///
/// This routine uses SimplifyInstruction to simplify 'I', and if successful
/// replaces uses of 'I' with the simplified value. It then recurses on each
/// of the users impacted. It returns true if any simplifications were
/// performed.
bool recursivelySimplifyInstruction(Instruction *I,
                                    const TargetLibraryInfo *TLI = nullptr,
                                    const DominatorTree *DT = nullptr,
                                    AssumptionCache *AC = nullptr);

// These helper functions return a SimplifyQuery structure that contains as
// many of the optional analysis we use as are currently valid.  This is the
// strongly preferred way of constructing SimplifyQuery in passes.
const SimplifyQuery getBestSimplifyQuery(Pass &, Function &);
template <class T, class... TArgs>
const SimplifyQuery getBestSimplifyQuery(AnalysisManager<T, TArgs...> &,
                                         Function &);
const SimplifyQuery getBestSimplifyQuery(LoopStandardAnalysisResults &,
                                         const DataLayout &);
} // end namespace llvm

#endif