BypassSlowDivision.h revision 360784 
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
25namespace llvm {
26
27class BasicBlock;
28class Value;
29
30struct 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
41template <> 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.
69bool 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