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;
32   Value *Dividend;
33   Value *Divisor;
34 
DivRemMapKeyDivRemMapKey35   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 
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.
65 bool 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