LLVM  6.0.0svn
BypassSlowDivision.h
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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 
25 namespace llvm {
26 
27 class BasicBlock;
28 class Value;
29 
30 struct DivRemMapKey {
31  bool SignedOp;
34 
35  DivRemMapKey(bool InSignedOp, Value *InDividend, Value *InDivisor)
36  : SignedOp(InSignedOp), Dividend(InDividend), Divisor(InDivisor) {}
37 };
38 
39 template <> 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 
46  return DivRemMapKey(false, nullptr, nullptr);
47  }
48 
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.
66  BasicBlock *BB, const DenseMap<unsigned int, unsigned int> &BypassWidth);
67 
68 } // end namespace llvm
69 
70 #endif // LLVM_TRANSFORMS_UTILS_BYPASSSLOWDIVISION_H
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
Various leaf nodes.
Definition: ISDOpcodes.h:60
bool bypassSlowDivision(BasicBlock *BB, const DenseMap< unsigned int, unsigned int > &BypassWidth)
This optimization identifies DIV instructions in a BB that can be profitably bypassed and carried out...
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
static unsigned getHashValue(const DivRemMapKey &Val)
static bool isEqual(const DivRemMapKey &Val1, const DivRemMapKey &Val2)
DivRemMapKey(bool InSignedOp, Value *InDividend, Value *InDivisor)
LLVM Value Representation.
Definition: Value.h:73