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