1 //===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- 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 holds routines to help analyse compare instructions 11 // and fold them into constants or other compare instructions 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_ANALYSIS_CMPINSTANALYSIS_H 16 #define LLVM_ANALYSIS_CMPINSTANALYSIS_H 17 18 #include "llvm/IR/InstrTypes.h" 19 20 namespace llvm { 21 class ICmpInst; 22 class Value; 23 24 /// Encode a icmp predicate into a three bit mask. These bits are carefully 25 /// arranged to allow folding of expressions such as: 26 /// 27 /// (A < B) | (A > B) --> (A != B) 28 /// 29 /// Note that this is only valid if the first and second predicates have the 30 /// same sign. It is illegal to do: (A u< B) | (A s> B) 31 /// 32 /// Three bits are used to represent the condition, as follows: 33 /// 0 A > B 34 /// 1 A == B 35 /// 2 A < B 36 /// 37 /// <=> Value Definition 38 /// 000 0 Always false 39 /// 001 1 A > B 40 /// 010 2 A == B 41 /// 011 3 A >= B 42 /// 100 4 A < B 43 /// 101 5 A != B 44 /// 110 6 A <= B 45 /// 111 7 Always true 46 /// 47 unsigned getICmpCode(const ICmpInst *ICI, bool InvertPred = false); 48 49 /// This is the complement of getICmpCode, which turns an opcode and two 50 /// operands into either a constant true or false, or the predicate for a new 51 /// ICmp instruction. The sign is passed in to determine which kind of 52 /// predicate to use in the new icmp instruction. 53 /// Non-NULL return value will be a true or false constant. 54 /// NULL return means a new ICmp is needed. The predicate for which is output 55 /// in NewICmpPred. 56 Value *getICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS, 57 CmpInst::Predicate &NewICmpPred); 58 59 /// Return true if both predicates match sign or if at least one of them is an 60 /// equality comparison (which is signless). 61 bool PredicatesFoldable(CmpInst::Predicate p1, CmpInst::Predicate p2); 62 63 /// Decompose an icmp into the form ((X & Mask) pred 0) if possible. The 64 /// returned predicate is either == or !=. Returns false if decomposition 65 /// fails. 66 bool decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate &Pred, 67 Value *&X, APInt &Mask, 68 bool LookThroughTrunc = true); 69 70 } // end namespace llvm 71 72 #endif 73
