include/llvm/Transforms/Utils/BypassSlowDivision.h

   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