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/IR/Constants.h" 17 #include "llvm/IR/Instructions.h" 18 19 using 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 /// 44 unsigned 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. 72 Value *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 nullptr; 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). 92 bool 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
