1//===- CmpInstAnalysis.cpp - Utils to help fold compares ---------------===//
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 holds routines to help analyse compare instructions
11// and fold them into constants or other compare instructions
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Transforms/Utils/CmpInstAnalysis.h"
16#include "llvm/Constants.h"
17#include "llvm/Instructions.h"
18
19using namespace llvm;
20
21/// getICmpCode - Encode a icmp predicate into a three bit mask.  These bits
22/// are carefully arranged to allow folding of expressions such as:
23///
24///      (A < B) | (A > B) --> (A != B)
25///
26/// Note that this is only valid if the first and second predicates have the
27/// same sign. Is illegal to do: (A u< B) | (A s> B)
28///
29/// Three bits are used to represent the condition, as follows:
30///   0  A > B
31///   1  A == B
32///   2  A < B
33///
34/// <=>  Value  Definition
35/// 000     0   Always false
36/// 001     1   A >  B
37/// 010     2   A == B
38/// 011     3   A >= B
39/// 100     4   A <  B
40/// 101     5   A != B
41/// 110     6   A <= B
42/// 111     7   Always true
43///
44unsigned llvm::getICmpCode(const ICmpInst *ICI, bool InvertPred) {
45  ICmpInst::Predicate Pred = InvertPred ? ICI->getInversePredicate()
46                                        : ICI->getPredicate();
47  switch (Pred) {
48      // False -> 0
49    case ICmpInst::ICMP_UGT: return 1;  // 001
50    case ICmpInst::ICMP_SGT: return 1;  // 001
51    case ICmpInst::ICMP_EQ:  return 2;  // 010
52    case ICmpInst::ICMP_UGE: return 3;  // 011
53    case ICmpInst::ICMP_SGE: return 3;  // 011
54    case ICmpInst::ICMP_ULT: return 4;  // 100
55    case ICmpInst::ICMP_SLT: return 4;  // 100
56    case ICmpInst::ICMP_NE:  return 5;  // 101
57    case ICmpInst::ICMP_ULE: return 6;  // 110
58    case ICmpInst::ICMP_SLE: return 6;  // 110
59      // True -> 7
60    default:
61      llvm_unreachable("Invalid ICmp predicate!");
62  }
63}
64
65/// getICmpValue - This is the complement of getICmpCode, which turns an
66/// opcode and two operands into either a constant true or false, or the
67/// predicate for a new ICmp instruction. The sign is passed in to determine
68/// which kind of predicate to use in the new icmp instruction.
69/// Non-NULL return value will be a true or false constant.
70/// NULL return means a new ICmp is needed.  The predicate for which is
71/// output in NewICmpPred.
72Value *llvm::getICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS,
73                          CmpInst::Predicate &NewICmpPred) {
74  switch (Code) {
75    default: llvm_unreachable("Illegal ICmp code!");
76    case 0: // False.
77      return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
78    case 1: NewICmpPred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break;
79    case 2: NewICmpPred = ICmpInst::ICMP_EQ; break;
80    case 3: NewICmpPred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break;
81    case 4: NewICmpPred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break;
82    case 5: NewICmpPred = ICmpInst::ICMP_NE; break;
83    case 6: NewICmpPred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break;
84    case 7: // True.
85      return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1);
86  }
87  return NULL;
88}
89
90/// PredicatesFoldable - Return true if both predicates match sign or if at
91/// least one of them is an equality comparison (which is signless).
92bool llvm::PredicatesFoldable(ICmpInst::Predicate p1, ICmpInst::Predicate p2) {
93  return (CmpInst::isSigned(p1) == CmpInst::isSigned(p2)) ||
94         (CmpInst::isSigned(p1) && ICmpInst::isEquality(p2)) ||
95         (CmpInst::isSigned(p2) && ICmpInst::isEquality(p1));
96}
97