ValueTracking.cpp revision d82e511aec0ea27ddd4c1e504b37f689796e965f
1173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner//===- ValueTracking.cpp - Walk computations to compute properties --------===// 2173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// 3173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// The LLVM Compiler Infrastructure 4173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// 5173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// This file is distributed under the University of Illinois Open Source 6173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// License. See LICENSE.TXT for details. 7173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// 8173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner//===----------------------------------------------------------------------===// 9173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// 10173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// This file contains routines that help analyze properties that chains of 11173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// computations have. 12173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner// 13173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner//===----------------------------------------------------------------------===// 14173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 15173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/Analysis/ValueTracking.h" 16173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/Constants.h" 17173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/Instructions.h" 18173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/IntrinsicInst.h" 19173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/Target/TargetData.h" 20173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/Support/GetElementPtrTypeIterator.h" 21173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner#include "llvm/Support/MathExtras.h" 22173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattnerusing namespace llvm; 23173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 24173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// getOpcode - If this is an Instruction or a ConstantExpr, return the 25173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// opcode value. Otherwise return UserOp1. 26173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattnerstatic unsigned getOpcode(const Value *V) { 27173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (const Instruction *I = dyn_cast<Instruction>(V)) 28173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return I->getOpcode(); 29173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 30173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return CE->getOpcode(); 31173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Use UserOp1 to mean there's no opcode. 32173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return Instruction::UserOp1; 33173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner} 34173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 35173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 36173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// ComputeMaskedBits - Determine which of the bits specified in Mask are 37173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// known to be either zero or one and return them in the KnownZero/KnownOne 38173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// bit sets. This code only analyzes bits in Mask, in order to short-circuit 39173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// processing. 40173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that 41173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// we cannot optimize based on the assumption that it is zero without changing 42173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// it to be an explicit zero. If we don't change it to zero, other code could 43173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// optimized based on the contradictory assumption that it is non-zero. 44173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// Because instcombine aggressively folds operations with undef args anyway, 45173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// this won't lose us code quality. 46173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattnervoid llvm::ComputeMaskedBits(Value *V, const APInt &Mask, 47173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt &KnownZero, APInt &KnownOne, 48173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TargetData *TD, unsigned Depth) { 49173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert(V && "No Value?"); 50173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert(Depth <= 6 && "Limit Search Depth"); 51173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint32_t BitWidth = Mask.getBitWidth(); 52173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) && 53173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner "Not integer or pointer type!"); 54173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) && 55173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner (!isa<IntegerType>(V->getType()) || 56173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner V->getType()->getPrimitiveSizeInBits() == BitWidth) && 57173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.getBitWidth() == BitWidth && 58173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.getBitWidth() == BitWidth && 59173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner "V, Mask, KnownOne and KnownZero should have same BitWidth"); 60173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 61173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 62173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // We know all of the bits for a constant! 63173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne = CI->getValue() & Mask; 64173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = ~KnownOne & Mask; 65173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 66173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 67173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Null is all-zeros. 68173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (isa<ConstantPointerNull>(V)) { 69173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.clear(); 70173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = Mask; 71173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 72173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 73173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // The address of an aligned GlobalValue has trailing zeros. 74173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 75173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned Align = GV->getAlignment(); 76173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) 77173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Align = TD->getPrefTypeAlignment(GV->getType()->getElementType()); 78173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Align > 0) 79173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = Mask & APInt::getLowBitsSet(BitWidth, 80173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner CountTrailingZeros_32(Align)); 81173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else 82173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.clear(); 83173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.clear(); 84173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 85173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 86173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 87173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything. 88173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 89173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Depth == 6 || Mask == 0) 90173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; // Limit search depth. 91173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 92173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner User *I = dyn_cast<User>(V); 93173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (!I) return; 94173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 95173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt KnownZero2(KnownZero), KnownOne2(KnownOne); 96173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner switch (getOpcode(I)) { 97173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner default: break; 98173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::And: { 99173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If either the LHS or the RHS are Zero, the result is zero. 100173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); 101173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2(Mask & ~KnownZero); 102173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 103173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 104173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 105173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 106173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 107173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-1 bits are only known if set in both the LHS & RHS. 108173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne &= KnownOne2; 109173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-0 are known to be clear if zero in either the LHS | RHS. 110173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= KnownZero2; 111173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 112173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 113173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Or: { 114173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); 115173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2(Mask & ~KnownOne); 116173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 117173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 118173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 119173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 120173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 121173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-0 bits are only known if clear in both the LHS & RHS. 122173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero &= KnownZero2; 123173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-1 are known to be set if set in either the LHS | RHS. 124173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne |= KnownOne2; 125173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 126173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 127173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Xor: { 128173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); 129173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD, 130173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 131173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 132173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 133173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 134173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-0 bits are known if clear or set in both the LHS & RHS. 135173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2); 136173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-1 are known to be set if set in only one of the LHS, RHS. 137173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2); 138173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = KnownZeroOut; 139173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 140173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 141173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Mul: { 142173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2 = APInt::getAllOnesValue(BitWidth); 143173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1); 144173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 145173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 146173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 147173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 148173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 149173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If low bits are zero in either operand, output low known-0 bits. 150173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Also compute a conserative estimate for high known-0 bits. 151173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // More trickiness is possible, but this is sufficient for the 152173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // interesting case of alignment computation. 153173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.clear(); 154173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned TrailZ = KnownZero.countTrailingOnes() + 155173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.countTrailingOnes(); 156173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned LeadZ = std::max(KnownZero.countLeadingOnes() + 157173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.countLeadingOnes(), 158173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner BitWidth) - BitWidth; 159173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 160173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TrailZ = std::min(TrailZ, BitWidth); 161173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LeadZ = std::min(LeadZ, BitWidth); 162173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) | 163173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt::getHighBitsSet(BitWidth, LeadZ); 164173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero &= Mask; 165173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 166173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 167173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::UDiv: { 168173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // For the purposes of computing leading zeros we can conservatively 169173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // treat a udiv as a logical right shift by the power of 2 known to 170173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // be less than the denominator. 171173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt AllOnes = APInt::getAllOnesValue(BitWidth); 172173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), 173173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner AllOnes, KnownZero2, KnownOne2, TD, Depth+1); 174173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned LeadZ = KnownZero2.countLeadingOnes(); 175173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 176173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne2.clear(); 177173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.clear(); 178173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), 179173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner AllOnes, KnownZero2, KnownOne2, TD, Depth+1); 180173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros(); 181173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (RHSUnknownLeadingOnes != BitWidth) 182173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LeadZ = std::min(BitWidth, 183173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LeadZ + BitWidth - RHSUnknownLeadingOnes - 1); 184173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 185173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask; 186173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 187173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 188173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Select: 189173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1); 190173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD, 191173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 192173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 193173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 194173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 195173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Only known if known in both the LHS and RHS. 196173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne &= KnownOne2; 197173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero &= KnownZero2; 198173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 199173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::FPTrunc: 200173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::FPExt: 201173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::FPToUI: 202173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::FPToSI: 203173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::SIToFP: 204173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::UIToFP: 205173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; // Can't work with floating point. 206173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::PtrToInt: 207173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::IntToPtr: 208173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // We can't handle these if we don't know the pointer size. 209173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (!TD) return; 210173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // FALL THROUGH and handle them the same as zext/trunc. 211173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::ZExt: 212173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Trunc: { 213173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Note that we handle pointer operands here because of inttoptr/ptrtoint 214173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // which fall through here. 215173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner const Type *SrcTy = I->getOperand(0)->getType(); 216173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint32_t SrcBitWidth = TD ? 217173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TD->getTypeSizeInBits(SrcTy) : 218173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner SrcTy->getPrimitiveSizeInBits(); 219173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt MaskIn(Mask); 220173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner MaskIn.zextOrTrunc(SrcBitWidth); 221173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.zextOrTrunc(SrcBitWidth); 222173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.zextOrTrunc(SrcBitWidth); 223173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD, 224173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 225173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.zextOrTrunc(BitWidth); 226173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.zextOrTrunc(BitWidth); 227173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Any top bits are known to be zero. 228173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (BitWidth > SrcBitWidth) 229173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); 230173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 231173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 232173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::BitCast: { 233173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner const Type *SrcTy = I->getOperand(0)->getType(); 234173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) { 235173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD, 236173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 237173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 238173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 239173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 240173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 241173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::SExt: { 242173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Compute the bits in the result that are not present in the input. 243173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType()); 244173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint32_t SrcBitWidth = SrcTy->getBitWidth(); 245173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 246173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt MaskIn(Mask); 247173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner MaskIn.trunc(SrcBitWidth); 248173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.trunc(SrcBitWidth); 249173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.trunc(SrcBitWidth); 250173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD, 251173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 252173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 253173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero.zext(BitWidth); 254173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.zext(BitWidth); 255173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 256173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If the sign bit of the input is known set or clear, then we know the 257173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // top bits of the result. 258173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero 259173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); 260173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set 261173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); 262173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 263173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 264173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Shl: 265173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 266173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { 267173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); 268173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2(Mask.lshr(ShiftAmt)); 269173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, 270173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 271173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 272173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero <<= ShiftAmt; 273173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne <<= ShiftAmt; 274173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0 275173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 276173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 277173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 278173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::LShr: 279173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 280173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { 281173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Compute the new bits that are at the top now. 282173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); 283173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 284173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Unsigned shift right. 285173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2(Mask.shl(ShiftAmt)); 286173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD, 287173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 288173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 289173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); 290173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); 291173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // high bits known zero. 292173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt); 293173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 294173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 295173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 296173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::AShr: 297173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 298173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { 299173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Compute the new bits that are at the top now. 300173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); 301173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 302173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Signed shift right. 303173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2(Mask.shl(ShiftAmt)); 304173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, 305173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 306173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 307173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); 308173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); 309173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 310173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt)); 311173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero. 312173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= HighBits; 313173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one. 314173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne |= HighBits; 315173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 316173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 317173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 318173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Sub: { 319173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) { 320173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // We know that the top bits of C-X are clear if X contains less bits 321173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // than C (i.e. no wrap-around can happen). For example, 20-X is 322173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // positive if we can prove that X is >= 0 and < 16. 323173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (!CLHS->getValue().isNegative()) { 324173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros(); 325173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // NLZ can't be BitWidth with no sign bit 326173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1); 327173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2, 328173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TD, Depth+1); 329173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 330173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If all of the MaskV bits are known to be zero, then we know the 331173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // output top bits are zero, because we now know that the output is 332173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // from [0-C]. 333173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if ((KnownZero2 & MaskV) == MaskV) { 334173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned NLZ2 = CLHS->getValue().countLeadingZeros(); 335173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Top bits known zero. 336173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask; 337173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 338173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 339173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 340173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 341173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // fall through 342173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Add: { 343173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Output known-0 bits are known if clear or set in both the low clear bits 344173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // common to both LHS & RHS. For example, 8+(X<<3) is known to have the 345173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // low 3 bits clear. 346173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2 = APInt::getLowBitsSet(BitWidth, Mask.countTrailingOnes()); 347173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 348173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 349173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 350173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned KnownZeroOut = KnownZero2.countTrailingOnes(); 351173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 352173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD, 353173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 354173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 355173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZeroOut = std::min(KnownZeroOut, 356173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.countTrailingOnes()); 357173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 358173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut); 359173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return; 360173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 361173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::SRem: 362173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { 363173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt RA = Rem->getValue(); 364173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (RA.isPowerOf2() || (-RA).isPowerOf2()) { 365173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA; 366173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2 = LowBits | APInt::getSignBit(BitWidth); 367173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 368173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 369173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 370173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // The sign of a remainder is equal to the sign of the first 371173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // operand (zero being positive). 372173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits)) 373173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2 |= ~LowBits; 374173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else if (KnownOne2[BitWidth-1]) 375173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne2 |= ~LowBits; 376173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 377173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= KnownZero2 & Mask; 378173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne |= KnownOne2 & Mask; 379173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 380173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 381173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 382173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 383173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 384173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::URem: { 385173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { 386173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt RA = Rem->getValue(); 387173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (RA.isPowerOf2()) { 388173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt LowBits = (RA - 1); 389173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2 = LowBits & Mask; 390173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero |= ~LowBits & Mask; 391173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, 392173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 393173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 394173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 395173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 396173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 397173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 398173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Since the result is less than or equal to either operand, any leading 399173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // zero bits in either operand must also exist in the result. 400173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt AllOnes = APInt::getAllOnesValue(BitWidth); 401173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne, 402173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TD, Depth+1); 403173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2, 404173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TD, Depth+1); 405173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 406173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint32_t Leaders = std::max(KnownZero.countLeadingOnes(), 407173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.countLeadingOnes()); 408173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne.clear(); 409173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask; 410173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 411173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 412173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 413173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Alloca: 414173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Malloc: { 415173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner AllocationInst *AI = cast<AllocationInst>(V); 416173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned Align = AI->getAlignment(); 417173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Align == 0 && TD) { 418173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (isa<AllocaInst>(AI)) 419173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Align = TD->getPrefTypeAlignment(AI->getType()->getElementType()); 420173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else if (isa<MallocInst>(AI)) { 421173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Malloc returns maximally aligned memory. 422173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Align = TD->getABITypeAlignment(AI->getType()->getElementType()); 423173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Align = 424173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner std::max(Align, 425173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner (unsigned)TD->getABITypeAlignment(Type::DoubleTy)); 426173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Align = 427173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner std::max(Align, 428173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner (unsigned)TD->getABITypeAlignment(Type::Int64Ty)); 429173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 430173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 431173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 432173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Align > 0) 433173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = Mask & APInt::getLowBitsSet(BitWidth, 434173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner CountTrailingZeros_32(Align)); 435173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 436173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 437173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::GetElementPtr: { 438173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Analyze all of the subscripts of this getelementptr instruction 439173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // to determine if we can prove known low zero bits. 440173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt LocalMask = APInt::getAllOnesValue(BitWidth); 441173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0); 442173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(I->getOperand(0), LocalMask, 443173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LocalKnownZero, LocalKnownOne, TD, Depth+1); 444173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned TrailZ = LocalKnownZero.countTrailingOnes(); 445173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 446173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner gep_type_iterator GTI = gep_type_begin(I); 447173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) { 448173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Value *Index = I->getOperand(i); 449173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 450173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Handle struct member offset arithmetic. 451173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (!TD) return; 452173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner const StructLayout *SL = TD->getStructLayout(STy); 453173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned Idx = cast<ConstantInt>(Index)->getZExtValue(); 454173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint64_t Offset = SL->getElementOffset(Idx); 455173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TrailZ = std::min(TrailZ, 456173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner CountTrailingZeros_64(Offset)); 457173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } else { 458173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Handle array index arithmetic. 459173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner const Type *IndexedTy = GTI.getIndexedType(); 460173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (!IndexedTy->isSized()) return; 461173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned GEPOpiBits = Index->getType()->getPrimitiveSizeInBits(); 462173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner uint64_t TypeSize = TD ? TD->getABITypeSize(IndexedTy) : 1; 463173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LocalMask = APInt::getAllOnesValue(GEPOpiBits); 464173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); 465173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(Index, LocalMask, 466173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LocalKnownZero, LocalKnownOne, TD, Depth+1); 467173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TrailZ = std::min(TrailZ, 468173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner CountTrailingZeros_64(TypeSize) + 469173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner LocalKnownZero.countTrailingOnes()); 470173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 471173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 472173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 473173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask; 474173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 475173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 476173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::PHI: { 477173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner PHINode *P = cast<PHINode>(I); 478173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Handle the case of a simple two-predecessor recurrence PHI. 479173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // There's a lot more that could theoretically be done here, but 480173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // this is sufficient to catch some interesting cases. 481173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (P->getNumIncomingValues() == 2) { 482173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner for (unsigned i = 0; i != 2; ++i) { 483173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Value *L = P->getIncomingValue(i); 484173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Value *R = P->getIncomingValue(!i); 485173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner User *LU = dyn_cast<User>(L); 486173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (!LU) 487173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner continue; 488173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned Opcode = getOpcode(LU); 489173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Check for operations that have the property that if 490173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // both their operands have low zero bits, the result 491173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // will have low zero bits. 492173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Opcode == Instruction::Add || 493173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Opcode == Instruction::Sub || 494173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Opcode == Instruction::And || 495173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Opcode == Instruction::Or || 496173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Opcode == Instruction::Mul) { 497173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Value *LL = LU->getOperand(0); 498173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Value *LR = LU->getOperand(1); 499173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Find a recurrence. 500173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (LL == I) 501173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner L = LR; 502173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else if (LR == I) 503173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner L = LL; 504173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner else 505173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 506173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Ok, we have a PHI of the form L op= R. Check for low 507173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // zero bits. 508173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask2 = APInt::getAllOnesValue(BitWidth); 509173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1); 510173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Mask2 = APInt::getLowBitsSet(BitWidth, 511173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.countTrailingOnes()); 512173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownOne2.clear(); 513173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.clear(); 514173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(L, Mask2, KnownZero2, KnownOne2, TD, Depth+1); 515173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = Mask & 516173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt::getLowBitsSet(BitWidth, 517173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero2.countTrailingOnes()); 518173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 519173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 520173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 521173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 522173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 523173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 524173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Call: 525173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 526173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner switch (II->getIntrinsicID()) { 527173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner default: break; 528173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Intrinsic::ctpop: 529173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Intrinsic::ctlz: 530173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Intrinsic::cttz: { 531173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned LowBits = Log2_32(BitWidth)+1; 532173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits); 533173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 534173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 535173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 536173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 537173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 538173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 539173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner} 540173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 541173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use 542173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// this predicate to simplify operations downstream. Mask is known to be zero 543173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// for bits that V cannot have. 544173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattnerbool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, 545173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TargetData *TD, unsigned Depth) { 546173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0); 547173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth); 548173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 549173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return (KnownZero & Mask) == Mask; 550173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner} 551173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 552173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 553173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 554173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// ComputeNumSignBits - Return the number of times the sign bit of the 555173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// register is replicated into the other bits. We know that at least 1 bit 556173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// is always equal to the sign bit (itself), but other cases can give us 557173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// information. For example, immediately after an "ashr X, 2", we know that 558173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// the top 3 bits are all equal to each other, so we return 3. 559173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// 560173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// 'Op' must have a scalar integer type. 561173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner/// 562173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattnerunsigned llvm::ComputeNumSignBits(Value *V, TargetData *TD, unsigned Depth) { 563173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner const IntegerType *Ty = cast<IntegerType>(V->getType()); 564173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned TyBits = Ty->getBitWidth(); 565173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned Tmp, Tmp2; 566173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner unsigned FirstAnswer = 1; 567173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 568d82e511aec0ea27ddd4c1e504b37f689796e965fChris Lattner // Note that ConstantInt is handled by the general ComputeMaskedBits case 569d82e511aec0ea27ddd4c1e504b37f689796e965fChris Lattner // below. 570d82e511aec0ea27ddd4c1e504b37f689796e965fChris Lattner 571173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Depth == 6) 572173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return 1; // Limit search depth. 573173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 574173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner User *U = dyn_cast<User>(V); 575173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner switch (getOpcode(V)) { 576173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner default: break; 577173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::SExt: 578173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = TyBits-cast<IntegerType>(U->getOperand(0)->getType())->getBitWidth(); 579173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp; 580173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 581173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::AShr: 582173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); 583173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // ashr X, C -> adds C sign bits. 584173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) { 585173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp += C->getZExtValue(); 586173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp > TyBits) Tmp = TyBits; 587173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 588173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return Tmp; 589173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Shl: 590173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) { 591173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // shl destroys sign bits. 592173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); 593173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (C->getZExtValue() >= TyBits || // Bad shift. 594173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner C->getZExtValue() >= Tmp) break; // Shifted all sign bits out. 595173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return Tmp - C->getZExtValue(); 596173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 597173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 598173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::And: 599173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Or: 600173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Xor: // NOT is handled here. 601173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Logical binary ops preserve the number of sign bits at the worst. 602173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); 603173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp != 1) { 604173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); 605173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner FirstAnswer = std::min(Tmp, Tmp2); 606173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // We computed what we know about the sign bits as our first 607173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // answer. Now proceed to the generic code that uses 608173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // ComputeMaskedBits, and pick whichever answer is better. 609173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 610173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 611173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 612173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Select: 613173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); 614173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp == 1) return 1; // Early out. 615173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1); 616173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return std::min(Tmp, Tmp2); 617173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 618173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Add: 619173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Add can have at most one carry bit. Thus we know that the output 620173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // is, at worst, one more bit than the inputs. 621173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); 622173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp == 1) return 1; // Early out. 623173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 624173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Special case decrementing a value (ADD X, -1): 625173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(0))) 626173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (CRHS->isAllOnesValue()) { 627173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); 628173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask = APInt::getAllOnesValue(TyBits); 629173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD, 630173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Depth+1); 631173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 632173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If the input is known to be 0 or 1, the output is 0/-1, which is all 633173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // sign bits set. 634173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if ((KnownZero | APInt(TyBits, 1)) == Mask) 635173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return TyBits; 636173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 637173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If we are subtracting one from a positive number, there is no carry 638173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // out of the result. 639173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (KnownZero.isNegative()) 640173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return Tmp; 641173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 642173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 643173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); 644173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp2 == 1) return 1; 645173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return std::min(Tmp, Tmp2)-1; 646173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 647173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 648173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Sub: 649173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); 650173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp2 == 1) return 1; 651173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 652173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Handle NEG. 653173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0))) 654173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (CLHS->isNullValue()) { 655173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); 656173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask = APInt::getAllOnesValue(TyBits); 657173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne, 658173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner TD, Depth+1); 659173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If the input is known to be 0 or 1, the output is 0/-1, which is all 660173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // sign bits set. 661173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if ((KnownZero | APInt(TyBits, 1)) == Mask) 662173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return TyBits; 663173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 664173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // If the input is known to be positive (the sign bit is known clear), 665173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // the output of the NEG has the same number of sign bits as the input. 666173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (KnownZero.isNegative()) 667173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return Tmp2; 668173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 669173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Otherwise, we treat this like a SUB. 670173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 671173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 672173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Sub can have at most one carry bit. Thus we know that the output 673173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // is, at worst, one more bit than the inputs. 674173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); 675173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (Tmp == 1) return 1; // Early out. 676173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return std::min(Tmp, Tmp2)-1; 677173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 678173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner case Instruction::Trunc: 679173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // FIXME: it's tricky to do anything useful for this, but it is an important 680173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // case for targets like X86. 681173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner break; 682173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 683173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 684173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Finally, if we can prove that the top bits of the result are 0's or 1's, 685173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // use this information. 686173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); 687173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner APInt Mask = APInt::getAllOnesValue(TyBits); 688173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth); 689173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 690173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner if (KnownZero.isNegative()) { // sign bit is 0 691173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Mask = KnownZero; 692173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } else if (KnownOne.isNegative()) { // sign bit is 1; 693173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Mask = KnownOne; 694173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } else { 695173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Nothing known. 696173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return FirstAnswer; 697173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner } 698173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner 699173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Okay, we know that the sign bit in Mask is set. Use CLZ to determine 700173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // the number of identical bits in the top of the input value. 701173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Mask = ~Mask; 702173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner Mask <<= Mask.getBitWidth()-TyBits; 703173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // Return # leading zeros. We use 'min' here in case Val was zero before 704173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner // shifting. We don't want to return '64' as for an i32 "0". 705173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros())); 706173234a68fb6ece106e77da443d87f09d5906cb9Chris Lattner} 707833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 708833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner/// CannotBeNegativeZero - Return true if we can prove that the specified FP 709833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner/// value is never equal to -0.0. 710833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner/// 711833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner/// NOTE: this function will need to be revisited when we support non-default 712833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner/// rounding modes! 713833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner/// 714833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattnerbool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) { 715833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V)) 716833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner return !CFP->getValueAPF().isNegZero(); 717833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 718833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (Depth == 6) 719833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner return 1; // Limit search depth. 720833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 721833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner const Instruction *I = dyn_cast<Instruction>(V); 722833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (I == 0) return false; 723833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 724833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner // (add x, 0.0) is guaranteed to return +0.0, not -0.0. 725833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (I->getOpcode() == Instruction::Add && 726833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner isa<ConstantFP>(I->getOperand(1)) && 727833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner cast<ConstantFP>(I->getOperand(1))->isNullValue()) 728833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner return true; 729833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 730833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner // sitofp and uitofp turn into +0.0 for zero. 731833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I)) 732833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner return true; 733833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 734833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) 735833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner // sqrt(-0.0) = -0.0, no other negative results are possible. 736833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (II->getIntrinsicID() == Intrinsic::sqrt) 737833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner return CannotBeNegativeZero(II->getOperand(1), Depth+1); 738833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 739833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (const CallInst *CI = dyn_cast<CallInst>(I)) 740833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (const Function *F = CI->getCalledFunction()) { 741833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (F->isDeclaration()) { 742833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner switch (F->getNameLen()) { 743833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner case 3: // abs(x) != -0.0 744833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (!strcmp(F->getNameStart(), "abs")) return true; 745833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner break; 746833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner case 4: // abs[lf](x) != -0.0 747833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (!strcmp(F->getNameStart(), "absf")) return true; 748833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner if (!strcmp(F->getNameStart(), "absl")) return true; 749833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner break; 750833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner } 751833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner } 752833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner } 753833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 754833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner return false; 755833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner} 756833f25d79ee28f1049f9177c3d2f4c9fbad6f643Chris Lattner 757