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//===- AggressiveInstCombineInternal.h --------------------------*- 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 implements the instruction pattern combiner classes.
// Currently, it handles pattern expressions for:
// * Truncate instruction
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallVector.h"
using namespace llvm;
// TruncInstCombine - looks for expression dags dominated by trunc instructions
// and for each eligible dag, it will create a reduced bit-width expression and
// replace the old expression with this new one and remove the old one.
// Eligible expression dag is such that:
// 1. Contains only supported instructions.
// 2. Supported leaves: ZExtInst, SExtInst, TruncInst and Constant value.
// 3. Can be evaluated into type with reduced legal bit-width (or Trunc type).
// 4. All instructions in the dag must not have users outside the dag.
// Only exception is for {ZExt, SExt}Inst with operand type equal to the
// new reduced type chosen in (3).
// The motivation for this optimization is that evaluating and expression using
// smaller bit-width is preferable, especially for vectorization where we can
// fit more values in one vectorized instruction. In addition, this optimization
// may decrease the number of cast instructions, but will not increase it.
namespace llvm {
class DataLayout;
class DominatorTree;
class Function;
class Instruction;
class TargetLibraryInfo;
class TruncInst;
class Type;
class Value;
class TruncInstCombine {
TargetLibraryInfo &TLI;
const DataLayout &DL;
const DominatorTree &DT;
/// List of all TruncInst instructions to be processed.
SmallVector<TruncInst *, 4> Worklist;
/// Current processed TruncInst instruction.
TruncInst *CurrentTruncInst;
/// Information per each instruction in the expression dag.
struct Info {
/// Number of LSBs that are needed to generate a valid expression.
unsigned ValidBitWidth = 0;
/// Minimum number of LSBs needed to generate the ValidBitWidth.
unsigned MinBitWidth = 0;
/// The reduced value generated to replace the old instruction.
Value *NewValue = nullptr;
/// An ordered map representing expression dag post-dominated by current
/// processed TruncInst. It maps each instruction in the dag to its Info
/// structure. The map is ordered such that each instruction appears before
/// all other instructions in the dag that uses it.
MapVector<Instruction *, Info> InstInfoMap;
TruncInstCombine(TargetLibraryInfo &TLI, const DataLayout &DL,
const DominatorTree &DT)
: TLI(TLI), DL(DL), DT(DT), CurrentTruncInst(nullptr) {}
/// Perform TruncInst pattern optimization on given function.
bool run(Function &F);
/// Build expression dag dominated by the /p CurrentTruncInst and append it to
/// the InstInfoMap container.
/// \return true only if succeed to generate an eligible sub expression dag.
bool buildTruncExpressionDag();
/// Calculate the minimal allowed bit-width of the chain ending with the
/// currently visited truncate's operand.
/// \return minimum number of bits to which the chain ending with the
/// truncate's operand can be shrunk to.
unsigned getMinBitWidth();
/// Build an expression dag dominated by the current processed TruncInst and
/// Check if it is eligible to be reduced to a smaller type.
/// \return the scalar version of the new type to be used for the reduced
/// expression dag, or nullptr if the expression dag is not eligible
/// to be reduced.
Type *getBestTruncatedType();
/// Given a \p V value and a \p SclTy scalar type return the generated reduced
/// value of \p V based on the type \p SclTy.
/// \param V value to be reduced.
/// \param SclTy scalar version of new type to reduce to.
/// \return the new reduced value.
Value *getReducedOperand(Value *V, Type *SclTy);
/// Create a new expression dag using the reduced /p SclTy type and replace
/// the old expression dag with it. Also erase all instructions in the old
/// dag, except those that are still needed outside the dag.
/// \param SclTy scalar version of new type to reduce expression dag into.
void ReduceExpressionDag(Type *SclTy);
} // end namespace llvm.