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      1 //===- llvm/Transforms/Utils/BypassSlowDivision.h ---------------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 // This file contains an optimization for div and rem on architectures that
     10 // execute short instructions significantly faster than longer instructions.
     11 // For example, on Intel Atom 32-bit divides are slow enough that during
     12 // runtime it is profitable to check the value of the operands, and if they are
     13 // positive and less than 256 use an unsigned 8-bit divide.
     14 //
     15 //===----------------------------------------------------------------------===//
     16 
     17 #ifndef LLVM_TRANSFORMS_UTILS_BYPASSSLOWDIVISION_H
     18 #define LLVM_TRANSFORMS_UTILS_BYPASSSLOWDIVISION_H
     19 
     20 #include "llvm/ADT/DenseMap.h"
     21 #include "llvm/ADT/DenseMapInfo.h"
     22 #include "llvm/IR/ValueHandle.h"
     23 #include <cstdint>
     24 
     25 namespace llvm {
     26 
     27 class BasicBlock;
     28 class Value;
     29 
     30 struct DivRemMapKey {
     31   bool SignedOp;
     32   AssertingVH<Value> Dividend;
     33   AssertingVH<Value> Divisor;
     34 
     35   DivRemMapKey() = default;
     36 
     37   DivRemMapKey(bool InSignedOp, Value *InDividend, Value *InDivisor)
     38       : SignedOp(InSignedOp), Dividend(InDividend), Divisor(InDivisor) {}
     39 };
     40 
     41 template <> struct DenseMapInfo<DivRemMapKey> {
     42   static bool isEqual(const DivRemMapKey &Val1, const DivRemMapKey &Val2) {
     43     return Val1.SignedOp == Val2.SignedOp && Val1.Dividend == Val2.Dividend &&
     44            Val1.Divisor == Val2.Divisor;
     45   }
     46 
     47   static DivRemMapKey getEmptyKey() {
     48     return DivRemMapKey(false, nullptr, nullptr);
     49   }
     50 
     51   static DivRemMapKey getTombstoneKey() {
     52     return DivRemMapKey(true, nullptr, nullptr);
     53   }
     54 
     55   static unsigned getHashValue(const DivRemMapKey &Val) {
     56     return (unsigned)(reinterpret_cast<uintptr_t>(
     57                           static_cast<Value *>(Val.Dividend)) ^
     58                       reinterpret_cast<uintptr_t>(
     59                           static_cast<Value *>(Val.Divisor))) ^
     60            (unsigned)Val.SignedOp;
     61   }
     62 };
     63 
     64 /// This optimization identifies DIV instructions in a BB that can be
     65 /// profitably bypassed and carried out with a shorter, faster divide.
     66 ///
     67 /// This optimization may add basic blocks immediately after BB; for obvious
     68 /// reasons, you shouldn't pass those blocks to bypassSlowDivision.
     69 bool bypassSlowDivision(
     70     BasicBlock *BB, const DenseMap<unsigned int, unsigned int> &BypassWidth);
     71 
     72 } // end namespace llvm
     73 
     74 #endif // LLVM_TRANSFORMS_UTILS_BYPASSSLOWDIVISION_H
     75