llvm/lib/Analysis/CmpInstAnalysis.cpp

   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
  19 using namespace llvm;
  20
  21 unsigned llvm::getICmpCode(CmpInst::Predicate Pred) {
  22   switch (Pred) {
  23       // False -> 0
  24     case ICmpInst::ICMP_UGT: return 1;  // 001
  25     case ICmpInst::ICMP_SGT: return 1;  // 001
  26     case ICmpInst::ICMP_EQ:  return 2;  // 010
  27     case ICmpInst::ICMP_UGE: return 3;  // 011
  28     case ICmpInst::ICMP_SGE: return 3;  // 011
  29     case ICmpInst::ICMP_ULT: return 4;  // 100
  30     case ICmpInst::ICMP_SLT: return 4;  // 100
  31     case ICmpInst::ICMP_NE:  return 5;  // 101
  32     case ICmpInst::ICMP_ULE: return 6;  // 110
  33     case ICmpInst::ICMP_SLE: return 6;  // 110
  34       // True -> 7
  35     default:
  36       llvm_unreachable("Invalid ICmp predicate!");
  37   }
  38 }
  39
  40 Constant *llvm::getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
  41                                    CmpInst::Predicate &Pred) {
  42   switch (Code) {
  43     default: llvm_unreachable("Illegal ICmp code!");
  44     case 0: // False.
  45       return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 0);
  46     case 1: Pred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break;
  47     case 2: Pred = ICmpInst::ICMP_EQ; break;
  48     case 3: Pred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break;
  49     case 4: Pred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break;
  50     case 5: Pred = ICmpInst::ICMP_NE; break;
  51     case 6: Pred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break;
  52     case 7: // True.
  53       return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 1);
  54   }
  55   return nullptr;
  56 }
  57
  58 bool llvm::predicatesFoldable(ICmpInst::Predicate P1, ICmpInst::Predicate P2) {
  59   return (CmpInst::isSigned(P1) == CmpInst::isSigned(P2)) ||
  60          (CmpInst::isSigned(P1) && ICmpInst::isEquality(P2)) ||
  61          (CmpInst::isSigned(P2) && ICmpInst::isEquality(P1));
  62 }
  63
  64 Constant *llvm::getPredForFCmpCode(unsigned Code, Type *OpTy,
  65                                    CmpInst::Predicate &Pred) {
  66   Pred = static_cast<FCmpInst::Predicate>(Code);
  67   assert(FCmpInst::FCMP_FALSE <= Pred && Pred <= FCmpInst::FCMP_TRUE &&
  68          "Unexpected FCmp predicate!");
  69   if (Pred == FCmpInst::FCMP_FALSE)
  70     return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 0);
  71   if (Pred == FCmpInst::FCMP_TRUE)
  72     return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 1);
  73   return nullptr;
  74 }
  75
  76 bool llvm::decomposeBitTestICmp(Value *LHS, Value *RHS,
  77                                 CmpInst::Predicate &Pred,
  78                                 Value *&X, APInt &Mask, bool LookThruTrunc) {
  79   using namespace PatternMatch;
  80
  81   const APInt *C;
  82   if (!match(RHS, m_APIntAllowUndef(C)))
  83     return false;
  84
  85   switch (Pred) {
  86   default:
  87     return false;
  88   case ICmpInst::ICMP_SLT:
  89     // X < 0 is equivalent to (X & SignMask) != 0.
  90     if (!C->isZero())
  91       return false;
  92     Mask = APInt::getSignMask(C->getBitWidth());
  93     Pred = ICmpInst::ICMP_NE;
  94     break;
  95   case ICmpInst::ICMP_SLE:
  96     // X <= -1 is equivalent to (X & SignMask) != 0.
  97     if (!C->isAllOnes())
  98       return false;
  99     Mask = APInt::getSignMask(C->getBitWidth());
 100     Pred = ICmpInst::ICMP_NE;
 101     break;
 102   case ICmpInst::ICMP_SGT:
 103     // X > -1 is equivalent to (X & SignMask) == 0.
 104     if (!C->isAllOnes())
 105       return false;
 106     Mask = APInt::getSignMask(C->getBitWidth());
 107     Pred = ICmpInst::ICMP_EQ;
 108     break;
 109   case ICmpInst::ICMP_SGE:
 110     // X >= 0 is equivalent to (X & SignMask) == 0.
 111     if (!C->isZero())
 112       return false;
 113     Mask = APInt::getSignMask(C->getBitWidth());
 114     Pred = ICmpInst::ICMP_EQ;
 115     break;
 116   case ICmpInst::ICMP_ULT:
 117     // X <u 2^n is equivalent to (X & ~(2^n-1)) == 0.
 118     if (!C->isPowerOf2())
 119       return false;
 120     Mask = -*C;
 121     Pred = ICmpInst::ICMP_EQ;
 122     break;
 123   case ICmpInst::ICMP_ULE:
 124     // X <=u 2^n-1 is equivalent to (X & ~(2^n-1)) == 0.
 125     if (!(*C + 1).isPowerOf2())
 126       return false;
 127     Mask = ~*C;
 128     Pred = ICmpInst::ICMP_EQ;
 129     break;
 130   case ICmpInst::ICMP_UGT:
 131     // X >u 2^n-1 is equivalent to (X & ~(2^n-1)) != 0.
 132     if (!(*C + 1).isPowerOf2())
 133       return false;
 134     Mask = ~*C;
 135     Pred = ICmpInst::ICMP_NE;
 136     break;
 137   case ICmpInst::ICMP_UGE:
 138     // X >=u 2^n is equivalent to (X & ~(2^n-1)) != 0.
 139     if (!C->isPowerOf2())
 140       return false;
 141     Mask = -*C;
 142     Pred = ICmpInst::ICMP_NE;
 143     break;
 144   }
 145
 146   if (LookThruTrunc && match(LHS, m_Trunc(m_Value(X)))) {
 147     Mask = Mask.zext(X->getType()->getScalarSizeInBits());
 148   } else {
 149     X = LHS;
 150   }
 151
 152   return true;
 153 }