1//===- CmpInstAnalysis.cpp - Utils to help fold compares ---------------===//
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 holds routines to help analyse compare instructions
10// and fold them into constants or other compare instructions
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Analysis/CmpInstAnalysis.h"
15#include "llvm/IR/Constants.h"
16#include "llvm/IR/Instructions.h"
17#include "llvm/IR/PatternMatch.h"
18
19using namespace llvm;
20
21unsigned llvm::getICmpCode(const ICmpInst *ICI, bool InvertPred) {
22  ICmpInst::Predicate Pred = InvertPred ? ICI->getInversePredicate()
23                                        : ICI->getPredicate();
24  switch (Pred) {
25      // False -> 0
26    case ICmpInst::ICMP_UGT: return 1;  // 001
27    case ICmpInst::ICMP_SGT: return 1;  // 001
28    case ICmpInst::ICMP_EQ:  return 2;  // 010
29    case ICmpInst::ICMP_UGE: return 3;  // 011
30    case ICmpInst::ICMP_SGE: return 3;  // 011
31    case ICmpInst::ICMP_ULT: return 4;  // 100
32    case ICmpInst::ICMP_SLT: return 4;  // 100
33    case ICmpInst::ICMP_NE:  return 5;  // 101
34    case ICmpInst::ICMP_ULE: return 6;  // 110
35    case ICmpInst::ICMP_SLE: return 6;  // 110
36      // True -> 7
37    default:
38      llvm_unreachable("Invalid ICmp predicate!");
39  }
40}
41
42Constant *llvm::getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
43                                   CmpInst::Predicate &Pred) {
44  switch (Code) {
45    default: llvm_unreachable("Illegal ICmp code!");
46    case 0: // False.
47      return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 0);
48    case 1: Pred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break;
49    case 2: Pred = ICmpInst::ICMP_EQ; break;
50    case 3: Pred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break;
51    case 4: Pred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break;
52    case 5: Pred = ICmpInst::ICMP_NE; break;
53    case 6: Pred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break;
54    case 7: // True.
55      return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 1);
56  }
57  return nullptr;
58}
59
60bool llvm::predicatesFoldable(ICmpInst::Predicate P1, ICmpInst::Predicate P2) {
61  return (CmpInst::isSigned(P1) == CmpInst::isSigned(P2)) ||
62         (CmpInst::isSigned(P1) && ICmpInst::isEquality(P2)) ||
63         (CmpInst::isSigned(P2) && ICmpInst::isEquality(P1));
64}
65
66bool llvm::decomposeBitTestICmp(Value *LHS, Value *RHS,
67                                CmpInst::Predicate &Pred,
68                                Value *&X, APInt &Mask, bool LookThruTrunc) {
69  using namespace PatternMatch;
70
71  const APInt *C;
72  if (!match(RHS, m_APInt(C)))
73    return false;
74
75  switch (Pred) {
76  default:
77    return false;
78  case ICmpInst::ICMP_SLT:
79    // X < 0 is equivalent to (X & SignMask) != 0.
80    if (!C->isNullValue())
81      return false;
82    Mask = APInt::getSignMask(C->getBitWidth());
83    Pred = ICmpInst::ICMP_NE;
84    break;
85  case ICmpInst::ICMP_SLE:
86    // X <= -1 is equivalent to (X & SignMask) != 0.
87    if (!C->isAllOnesValue())
88      return false;
89    Mask = APInt::getSignMask(C->getBitWidth());
90    Pred = ICmpInst::ICMP_NE;
91    break;
92  case ICmpInst::ICMP_SGT:
93    // X > -1 is equivalent to (X & SignMask) == 0.
94    if (!C->isAllOnesValue())
95      return false;
96    Mask = APInt::getSignMask(C->getBitWidth());
97    Pred = ICmpInst::ICMP_EQ;
98    break;
99  case ICmpInst::ICMP_SGE:
100    // X >= 0 is equivalent to (X & SignMask) == 0.
101    if (!C->isNullValue())
102      return false;
103    Mask = APInt::getSignMask(C->getBitWidth());
104    Pred = ICmpInst::ICMP_EQ;
105    break;
106  case ICmpInst::ICMP_ULT:
107    // X <u 2^n is equivalent to (X & ~(2^n-1)) == 0.
108    if (!C->isPowerOf2())
109      return false;
110    Mask = -*C;
111    Pred = ICmpInst::ICMP_EQ;
112    break;
113  case ICmpInst::ICMP_ULE:
114    // X <=u 2^n-1 is equivalent to (X & ~(2^n-1)) == 0.
115    if (!(*C + 1).isPowerOf2())
116      return false;
117    Mask = ~*C;
118    Pred = ICmpInst::ICMP_EQ;
119    break;
120  case ICmpInst::ICMP_UGT:
121    // X >u 2^n-1 is equivalent to (X & ~(2^n-1)) != 0.
122    if (!(*C + 1).isPowerOf2())
123      return false;
124    Mask = ~*C;
125    Pred = ICmpInst::ICMP_NE;
126    break;
127  case ICmpInst::ICMP_UGE:
128    // X >=u 2^n is equivalent to (X & ~(2^n-1)) != 0.
129    if (!C->isPowerOf2())
130      return false;
131    Mask = -*C;
132    Pred = ICmpInst::ICMP_NE;
133    break;
134  }
135
136  if (LookThruTrunc && match(LHS, m_Trunc(m_Value(X)))) {
137    Mask = Mask.zext(X->getType()->getScalarSizeInBits());
138  } else {
139    X = LHS;
140  }
141
142  return true;
143}
144