--- /dev/null
+//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains routines that help analyze properties that chains of
+// computations have.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_VALUETRACKING_H
+#define LLVM_ANALYSIS_VALUETRACKING_H
+
+namespace llvm {
+ class Value;
+ class APInt;
+ class TargetData;
+
+ /// ComputeMaskedBits - Determine which of the bits specified in Mask are
+ /// known to be either zero or one and return them in the KnownZero/KnownOne
+ /// bit sets. This code only analyzes bits in Mask, in order to short-circuit
+ /// processing.
+ void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
+ APInt &KnownOne, TargetData *TD = 0,
+ unsigned Depth = 0);
+
+ bool MaskedValueIsZero(Value *V, const APInt &Mask,
+ TargetData *TD = 0, unsigned Depth = 0);
+
+
+ /// ComputeNumSignBits - Return the number of times the sign bit of the
+ /// register is replicated into the other bits. We know that at least 1 bit
+ /// is always equal to the sign bit (itself), but other cases can give us
+ /// information. For example, immediately after an "ashr X, 2", we know that
+ /// the top 3 bits are all equal to each other, so we return 3.
+ ///
+ /// 'Op' must have a scalar integer type.
+ ///
+ unsigned ComputeNumSignBits(Value *Op, TargetData *TD = 0,
+ unsigned Depth = 0);
+
+} // end namespace llvm
+
+#endif
--- /dev/null
+//===- ValueTracking.cpp - Walk computations to compute properties --------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains routines that help analyze properties that chains of
+// computations have.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/MathExtras.h"
+using namespace llvm;
+
+/// getOpcode - If this is an Instruction or a ConstantExpr, return the
+/// opcode value. Otherwise return UserOp1.
+static unsigned getOpcode(const Value *V) {
+ if (const Instruction *I = dyn_cast<Instruction>(V))
+ return I->getOpcode();
+ if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
+ return CE->getOpcode();
+ // Use UserOp1 to mean there's no opcode.
+ return Instruction::UserOp1;
+}
+
+
+/// ComputeMaskedBits - Determine which of the bits specified in Mask are
+/// known to be either zero or one and return them in the KnownZero/KnownOne
+/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
+/// processing.
+/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
+/// we cannot optimize based on the assumption that it is zero without changing
+/// it to be an explicit zero. If we don't change it to zero, other code could
+/// optimized based on the contradictory assumption that it is non-zero.
+/// Because instcombine aggressively folds operations with undef args anyway,
+/// this won't lose us code quality.
+void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
+ APInt &KnownZero, APInt &KnownOne,
+ TargetData *TD, unsigned Depth) {
+ assert(V && "No Value?");
+ assert(Depth <= 6 && "Limit Search Depth");
+ uint32_t BitWidth = Mask.getBitWidth();
+ assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) &&
+ "Not integer or pointer type!");
+ assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) &&
+ (!isa<IntegerType>(V->getType()) ||
+ V->getType()->getPrimitiveSizeInBits() == BitWidth) &&
+ KnownZero.getBitWidth() == BitWidth &&
+ KnownOne.getBitWidth() == BitWidth &&
+ "V, Mask, KnownOne and KnownZero should have same BitWidth");
+
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
+ // We know all of the bits for a constant!
+ KnownOne = CI->getValue() & Mask;
+ KnownZero = ~KnownOne & Mask;
+ return;
+ }
+ // Null is all-zeros.
+ if (isa<ConstantPointerNull>(V)) {
+ KnownOne.clear();
+ KnownZero = Mask;
+ return;
+ }
+ // The address of an aligned GlobalValue has trailing zeros.
+ if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
+ unsigned Align = GV->getAlignment();
+ if (Align == 0 && TD && GV->getType()->getElementType()->isSized())
+ Align = TD->getPrefTypeAlignment(GV->getType()->getElementType());
+ if (Align > 0)
+ KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
+ CountTrailingZeros_32(Align));
+ else
+ KnownZero.clear();
+ KnownOne.clear();
+ return;
+ }
+
+ KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything.
+
+ if (Depth == 6 || Mask == 0)
+ return; // Limit search depth.
+
+ User *I = dyn_cast<User>(V);
+ if (!I) return;
+
+ APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
+ switch (getOpcode(I)) {
+ default: break;
+ case Instruction::And: {
+ // If either the LHS or the RHS are Zero, the result is zero.
+ ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
+ APInt Mask2(Mask & ~KnownZero);
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-1 bits are only known if set in both the LHS & RHS.
+ KnownOne &= KnownOne2;
+ // Output known-0 are known to be clear if zero in either the LHS | RHS.
+ KnownZero |= KnownZero2;
+ return;
+ }
+ case Instruction::Or: {
+ ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
+ APInt Mask2(Mask & ~KnownOne);
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-0 bits are only known if clear in both the LHS & RHS.
+ KnownZero &= KnownZero2;
+ // Output known-1 are known to be set if set in either the LHS | RHS.
+ KnownOne |= KnownOne2;
+ return;
+ }
+ case Instruction::Xor: {
+ ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
+ ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-0 bits are known if clear or set in both the LHS & RHS.
+ APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
+ // Output known-1 are known to be set if set in only one of the LHS, RHS.
+ KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
+ KnownZero = KnownZeroOut;
+ return;
+ }
+ case Instruction::Mul: {
+ APInt Mask2 = APInt::getAllOnesValue(BitWidth);
+ ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1);
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // If low bits are zero in either operand, output low known-0 bits.
+ // Also compute a conserative estimate for high known-0 bits.
+ // More trickiness is possible, but this is sufficient for the
+ // interesting case of alignment computation.
+ KnownOne.clear();
+ unsigned TrailZ = KnownZero.countTrailingOnes() +
+ KnownZero2.countTrailingOnes();
+ unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
+ KnownZero2.countLeadingOnes(),
+ BitWidth) - BitWidth;
+
+ TrailZ = std::min(TrailZ, BitWidth);
+ LeadZ = std::min(LeadZ, BitWidth);
+ KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
+ APInt::getHighBitsSet(BitWidth, LeadZ);
+ KnownZero &= Mask;
+ return;
+ }
+ case Instruction::UDiv: {
+ // For the purposes of computing leading zeros we can conservatively
+ // treat a udiv as a logical right shift by the power of 2 known to
+ // be less than the denominator.
+ APInt AllOnes = APInt::getAllOnesValue(BitWidth);
+ ComputeMaskedBits(I->getOperand(0),
+ AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
+ unsigned LeadZ = KnownZero2.countLeadingOnes();
+
+ KnownOne2.clear();
+ KnownZero2.clear();
+ ComputeMaskedBits(I->getOperand(1),
+ AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
+ unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
+ if (RHSUnknownLeadingOnes != BitWidth)
+ LeadZ = std::min(BitWidth,
+ LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
+
+ KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
+ return;
+ }
+ case Instruction::Select:
+ ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1);
+ ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Only known if known in both the LHS and RHS.
+ KnownOne &= KnownOne2;
+ KnownZero &= KnownZero2;
+ return;
+ case Instruction::FPTrunc:
+ case Instruction::FPExt:
+ case Instruction::FPToUI:
+ case Instruction::FPToSI:
+ case Instruction::SIToFP:
+ case Instruction::UIToFP:
+ return; // Can't work with floating point.
+ case Instruction::PtrToInt:
+ case Instruction::IntToPtr:
+ // We can't handle these if we don't know the pointer size.
+ if (!TD) return;
+ // FALL THROUGH and handle them the same as zext/trunc.
+ case Instruction::ZExt:
+ case Instruction::Trunc: {
+ // Note that we handle pointer operands here because of inttoptr/ptrtoint
+ // which fall through here.
+ const Type *SrcTy = I->getOperand(0)->getType();
+ uint32_t SrcBitWidth = TD ?
+ TD->getTypeSizeInBits(SrcTy) :
+ SrcTy->getPrimitiveSizeInBits();
+ APInt MaskIn(Mask);
+ MaskIn.zextOrTrunc(SrcBitWidth);
+ KnownZero.zextOrTrunc(SrcBitWidth);
+ KnownOne.zextOrTrunc(SrcBitWidth);
+ ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
+ Depth+1);
+ KnownZero.zextOrTrunc(BitWidth);
+ KnownOne.zextOrTrunc(BitWidth);
+ // Any top bits are known to be zero.
+ if (BitWidth > SrcBitWidth)
+ KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
+ return;
+ }
+ case Instruction::BitCast: {
+ const Type *SrcTy = I->getOperand(0)->getType();
+ if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) {
+ ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD,
+ Depth+1);
+ return;
+ }
+ break;
+ }
+ case Instruction::SExt: {
+ // Compute the bits in the result that are not present in the input.
+ const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
+ uint32_t SrcBitWidth = SrcTy->getBitWidth();
+
+ APInt MaskIn(Mask);
+ MaskIn.trunc(SrcBitWidth);
+ KnownZero.trunc(SrcBitWidth);
+ KnownOne.trunc(SrcBitWidth);
+ ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ KnownZero.zext(BitWidth);
+ KnownOne.zext(BitWidth);
+
+ // If the sign bit of the input is known set or clear, then we know the
+ // top bits of the result.
+ if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
+ KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
+ else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
+ KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
+ return;
+ }
+ case Instruction::Shl:
+ // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
+ if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
+ APInt Mask2(Mask.lshr(ShiftAmt));
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ KnownZero <<= ShiftAmt;
+ KnownOne <<= ShiftAmt;
+ KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
+ return;
+ }
+ break;
+ case Instruction::LShr:
+ // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
+ if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ // Compute the new bits that are at the top now.
+ uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
+
+ // Unsigned shift right.
+ APInt Mask2(Mask.shl(ShiftAmt));
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
+ KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
+ KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
+ // high bits known zero.
+ KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
+ return;
+ }
+ break;
+ case Instruction::AShr:
+ // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
+ if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ // Compute the new bits that are at the top now.
+ uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
+
+ // Signed shift right.
+ APInt Mask2(Mask.shl(ShiftAmt));
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
+ KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
+ KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
+
+ APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
+ if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
+ KnownZero |= HighBits;
+ else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
+ KnownOne |= HighBits;
+ return;
+ }
+ break;
+ case Instruction::Sub: {
+ if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) {
+ // We know that the top bits of C-X are clear if X contains less bits
+ // than C (i.e. no wrap-around can happen). For example, 20-X is
+ // positive if we can prove that X is >= 0 and < 16.
+ if (!CLHS->getValue().isNegative()) {
+ unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
+ // NLZ can't be BitWidth with no sign bit
+ APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
+ ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
+ TD, Depth+1);
+
+ // If all of the MaskV bits are known to be zero, then we know the
+ // output top bits are zero, because we now know that the output is
+ // from [0-C].
+ if ((KnownZero2 & MaskV) == MaskV) {
+ unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
+ // Top bits known zero.
+ KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
+ }
+ }
+ }
+ }
+ // fall through
+ case Instruction::Add: {
+ // Output known-0 bits are known if clear or set in both the low clear bits
+ // common to both LHS & RHS. For example, 8+(X<<3) is known to have the
+ // low 3 bits clear.
+ APInt Mask2 = APInt::getLowBitsSet(BitWidth, Mask.countTrailingOnes());
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+ unsigned KnownZeroOut = KnownZero2.countTrailingOnes();
+
+ ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD,
+ Depth+1);
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+ KnownZeroOut = std::min(KnownZeroOut,
+ KnownZero2.countTrailingOnes());
+
+ KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut);
+ return;
+ }
+ case Instruction::SRem:
+ if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ APInt RA = Rem->getValue();
+ if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
+ APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
+ APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
+ Depth+1);
+
+ // The sign of a remainder is equal to the sign of the first
+ // operand (zero being positive).
+ if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
+ KnownZero2 |= ~LowBits;
+ else if (KnownOne2[BitWidth-1])
+ KnownOne2 |= ~LowBits;
+
+ KnownZero |= KnownZero2 & Mask;
+ KnownOne |= KnownOne2 & Mask;
+
+ assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
+ }
+ }
+ break;
+ case Instruction::URem: {
+ if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ APInt RA = Rem->getValue();
+ if (RA.isPowerOf2()) {
+ APInt LowBits = (RA - 1);
+ APInt Mask2 = LowBits & Mask;
+ KnownZero |= ~LowBits & Mask;
+ ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
+ Depth+1);
+ assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
+ break;
+ }
+ }
+
+ // Since the result is less than or equal to either operand, any leading
+ // zero bits in either operand must also exist in the result.
+ APInt AllOnes = APInt::getAllOnesValue(BitWidth);
+ ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne,
+ TD, Depth+1);
+ ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
+ TD, Depth+1);
+
+ uint32_t Leaders = std::max(KnownZero.countLeadingOnes(),
+ KnownZero2.countLeadingOnes());
+ KnownOne.clear();
+ KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
+ break;
+ }
+
+ case Instruction::Alloca:
+ case Instruction::Malloc: {
+ AllocationInst *AI = cast<AllocationInst>(V);
+ unsigned Align = AI->getAlignment();
+ if (Align == 0 && TD) {
+ if (isa<AllocaInst>(AI))
+ Align = TD->getPrefTypeAlignment(AI->getType()->getElementType());
+ else if (isa<MallocInst>(AI)) {
+ // Malloc returns maximally aligned memory.
+ Align = TD->getABITypeAlignment(AI->getType()->getElementType());
+ Align =
+ std::max(Align,
+ (unsigned)TD->getABITypeAlignment(Type::DoubleTy));
+ Align =
+ std::max(Align,
+ (unsigned)TD->getABITypeAlignment(Type::Int64Ty));
+ }
+ }
+
+ if (Align > 0)
+ KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
+ CountTrailingZeros_32(Align));
+ break;
+ }
+ case Instruction::GetElementPtr: {
+ // Analyze all of the subscripts of this getelementptr instruction
+ // to determine if we can prove known low zero bits.
+ APInt LocalMask = APInt::getAllOnesValue(BitWidth);
+ APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
+ ComputeMaskedBits(I->getOperand(0), LocalMask,
+ LocalKnownZero, LocalKnownOne, TD, Depth+1);
+ unsigned TrailZ = LocalKnownZero.countTrailingOnes();
+
+ gep_type_iterator GTI = gep_type_begin(I);
+ for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
+ Value *Index = I->getOperand(i);
+ if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
+ // Handle struct member offset arithmetic.
+ if (!TD) return;
+ const StructLayout *SL = TD->getStructLayout(STy);
+ unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
+ uint64_t Offset = SL->getElementOffset(Idx);
+ TrailZ = std::min(TrailZ,
+ CountTrailingZeros_64(Offset));
+ } else {
+ // Handle array index arithmetic.
+ const Type *IndexedTy = GTI.getIndexedType();
+ if (!IndexedTy->isSized()) return;
+ unsigned GEPOpiBits = Index->getType()->getPrimitiveSizeInBits();
+ uint64_t TypeSize = TD ? TD->getABITypeSize(IndexedTy) : 1;
+ LocalMask = APInt::getAllOnesValue(GEPOpiBits);
+ LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
+ ComputeMaskedBits(Index, LocalMask,
+ LocalKnownZero, LocalKnownOne, TD, Depth+1);
+ TrailZ = std::min(TrailZ,
+ CountTrailingZeros_64(TypeSize) +
+ LocalKnownZero.countTrailingOnes());
+ }
+ }
+
+ KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
+ break;
+ }
+ case Instruction::PHI: {
+ PHINode *P = cast<PHINode>(I);
+ // Handle the case of a simple two-predecessor recurrence PHI.
+ // There's a lot more that could theoretically be done here, but
+ // this is sufficient to catch some interesting cases.
+ if (P->getNumIncomingValues() == 2) {
+ for (unsigned i = 0; i != 2; ++i) {
+ Value *L = P->getIncomingValue(i);
+ Value *R = P->getIncomingValue(!i);
+ User *LU = dyn_cast<User>(L);
+ if (!LU)
+ continue;
+ unsigned Opcode = getOpcode(LU);
+ // Check for operations that have the property that if
+ // both their operands have low zero bits, the result
+ // will have low zero bits.
+ if (Opcode == Instruction::Add ||
+ Opcode == Instruction::Sub ||
+ Opcode == Instruction::And ||
+ Opcode == Instruction::Or ||
+ Opcode == Instruction::Mul) {
+ Value *LL = LU->getOperand(0);
+ Value *LR = LU->getOperand(1);
+ // Find a recurrence.
+ if (LL == I)
+ L = LR;
+ else if (LR == I)
+ L = LL;
+ else
+ break;
+ // Ok, we have a PHI of the form L op= R. Check for low
+ // zero bits.
+ APInt Mask2 = APInt::getAllOnesValue(BitWidth);
+ ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
+ Mask2 = APInt::getLowBitsSet(BitWidth,
+ KnownZero2.countTrailingOnes());
+ KnownOne2.clear();
+ KnownZero2.clear();
+ ComputeMaskedBits(L, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
+ KnownZero = Mask &
+ APInt::getLowBitsSet(BitWidth,
+ KnownZero2.countTrailingOnes());
+ break;
+ }
+ }
+ }
+ break;
+ }
+ case Instruction::Call:
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default: break;
+ case Intrinsic::ctpop:
+ case Intrinsic::ctlz:
+ case Intrinsic::cttz: {
+ unsigned LowBits = Log2_32(BitWidth)+1;
+ KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
+ break;
+ }
+ }
+ }
+ break;
+ }
+}
+
+/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
+/// this predicate to simplify operations downstream. Mask is known to be zero
+/// for bits that V cannot have.
+bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask,
+ TargetData *TD, unsigned Depth) {
+ APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
+ ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ return (KnownZero & Mask) == Mask;
+}
+
+
+
+/// ComputeNumSignBits - Return the number of times the sign bit of the
+/// register is replicated into the other bits. We know that at least 1 bit
+/// is always equal to the sign bit (itself), but other cases can give us
+/// information. For example, immediately after an "ashr X, 2", we know that
+/// the top 3 bits are all equal to each other, so we return 3.
+///
+/// 'Op' must have a scalar integer type.
+///
+unsigned llvm::ComputeNumSignBits(Value *V, TargetData *TD, unsigned Depth) {
+ const IntegerType *Ty = cast<IntegerType>(V->getType());
+ unsigned TyBits = Ty->getBitWidth();
+ unsigned Tmp, Tmp2;
+ unsigned FirstAnswer = 1;
+
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
+ if (CI->getValue().isNegative())
+ return CI->getValue().countLeadingOnes();
+ return CI->getValue().countLeadingZeros();
+ }
+
+ if (Depth == 6)
+ return 1; // Limit search depth.
+
+ User *U = dyn_cast<User>(V);
+ switch (getOpcode(V)) {
+ default: break;
+ case Instruction::SExt:
+ Tmp = TyBits-cast<IntegerType>(U->getOperand(0)->getType())->getBitWidth();
+ return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp;
+
+ case Instruction::AShr:
+ Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
+ // ashr X, C -> adds C sign bits.
+ if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
+ Tmp += C->getZExtValue();
+ if (Tmp > TyBits) Tmp = TyBits;
+ }
+ return Tmp;
+ case Instruction::Shl:
+ if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
+ // shl destroys sign bits.
+ Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
+ if (C->getZExtValue() >= TyBits || // Bad shift.
+ C->getZExtValue() >= Tmp) break; // Shifted all sign bits out.
+ return Tmp - C->getZExtValue();
+ }
+ break;
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor: // NOT is handled here.
+ // Logical binary ops preserve the number of sign bits at the worst.
+ Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
+ if (Tmp != 1) {
+ Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
+ FirstAnswer = std::min(Tmp, Tmp2);
+ // We computed what we know about the sign bits as our first
+ // answer. Now proceed to the generic code that uses
+ // ComputeMaskedBits, and pick whichever answer is better.
+ }
+ break;
+
+ case Instruction::Select:
+ Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
+ if (Tmp == 1) return 1; // Early out.
+ Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1);
+ return std::min(Tmp, Tmp2);
+
+ case Instruction::Add:
+ // Add can have at most one carry bit. Thus we know that the output
+ // is, at worst, one more bit than the inputs.
+ Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
+ if (Tmp == 1) return 1; // Early out.
+
+ // Special case decrementing a value (ADD X, -1):
+ if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(0)))
+ if (CRHS->isAllOnesValue()) {
+ APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
+ APInt Mask = APInt::getAllOnesValue(TyBits);
+ ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD,
+ Depth+1);
+
+ // If the input is known to be 0 or 1, the output is 0/-1, which is all
+ // sign bits set.
+ if ((KnownZero | APInt(TyBits, 1)) == Mask)
+ return TyBits;
+
+ // If we are subtracting one from a positive number, there is no carry
+ // out of the result.
+ if (KnownZero.isNegative())
+ return Tmp;
+ }
+
+ Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
+ if (Tmp2 == 1) return 1;
+ return std::min(Tmp, Tmp2)-1;
+ break;
+
+ case Instruction::Sub:
+ Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
+ if (Tmp2 == 1) return 1;
+
+ // Handle NEG.
+ if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0)))
+ if (CLHS->isNullValue()) {
+ APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
+ APInt Mask = APInt::getAllOnesValue(TyBits);
+ ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne,
+ TD, Depth+1);
+ // If the input is known to be 0 or 1, the output is 0/-1, which is all
+ // sign bits set.
+ if ((KnownZero | APInt(TyBits, 1)) == Mask)
+ return TyBits;
+
+ // If the input is known to be positive (the sign bit is known clear),
+ // the output of the NEG has the same number of sign bits as the input.
+ if (KnownZero.isNegative())
+ return Tmp2;
+
+ // Otherwise, we treat this like a SUB.
+ }
+
+ // Sub can have at most one carry bit. Thus we know that the output
+ // is, at worst, one more bit than the inputs.
+ Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
+ if (Tmp == 1) return 1; // Early out.
+ return std::min(Tmp, Tmp2)-1;
+ break;
+ case Instruction::Trunc:
+ // FIXME: it's tricky to do anything useful for this, but it is an important
+ // case for targets like X86.
+ break;
+ }
+
+ // Finally, if we can prove that the top bits of the result are 0's or 1's,
+ // use this information.
+ APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
+ APInt Mask = APInt::getAllOnesValue(TyBits);
+ ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
+
+ if (KnownZero.isNegative()) { // sign bit is 0
+ Mask = KnownZero;
+ } else if (KnownOne.isNegative()) { // sign bit is 1;
+ Mask = KnownOne;
+ } else {
+ // Nothing known.
+ return FirstAnswer;
+ }
+
+ // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
+ // the number of identical bits in the top of the input value.
+ Mask = ~Mask;
+ Mask <<= Mask.getBitWidth()-TyBits;
+ // Return # leading zeros. We use 'min' here in case Val was zero before
+ // shifting. We don't want to return '64' as for an i32 "0".
+ return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
+}
#include "llvm/DerivedTypes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
I.eraseFromParent();
return 0; // Don't do anything with FI
}
+
+ void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
+ APInt &KnownOne, unsigned Depth = 0) const {
+ return llvm::ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
+ }
+
+ bool MaskedValueIsZero(Value *V, const APInt &Mask,
+ unsigned Depth = 0) const {
+ return llvm::MaskedValueIsZero(V, Mask, TD, Depth);
+ }
+ unsigned ComputeNumSignBits(Value *Op, unsigned Depth = 0) const {
+ return llvm::ComputeNumSignBits(Op, TD, Depth);
+ }
private:
/// InsertOperandCastBefore - This inserts a cast of V to DestTy before the
Value *EvaluateInDifferentType(Value *V, const Type *Ty, bool isSigned);
- void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
- APInt& KnownOne, unsigned Depth = 0) const;
- bool MaskedValueIsZero(Value *V, const APInt& Mask, unsigned Depth = 0);
- unsigned ComputeNumSignBits(Value *Op, unsigned Depth = 0) const;
bool CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
unsigned CastOpc,
int &NumCastsRemoved);
return MulExt.ugt(APInt::getLowBitsSet(W * 2, W));
}
-/// ComputeMaskedBits - Determine which of the bits specified in Mask are
-/// known to be either zero or one and return them in the KnownZero/KnownOne
-/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
-/// processing.
-/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
-/// we cannot optimize based on the assumption that it is zero without changing
-/// it to be an explicit zero. If we don't change it to zero, other code could
-/// optimized based on the contradictory assumption that it is non-zero.
-/// Because instcombine aggressively folds operations with undef args anyway,
-/// this won't lose us code quality.
-void InstCombiner::ComputeMaskedBits(Value *V, const APInt &Mask,
- APInt& KnownZero, APInt& KnownOne,
- unsigned Depth) const {
- assert(V && "No Value?");
- assert(Depth <= 6 && "Limit Search Depth");
- uint32_t BitWidth = Mask.getBitWidth();
- assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) &&
- "Not integer or pointer type!");
- assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) &&
- (!isa<IntegerType>(V->getType()) ||
- V->getType()->getPrimitiveSizeInBits() == BitWidth) &&
- KnownZero.getBitWidth() == BitWidth &&
- KnownOne.getBitWidth() == BitWidth &&
- "V, Mask, KnownOne and KnownZero should have same BitWidth");
-
- if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
- // We know all of the bits for a constant!
- KnownOne = CI->getValue() & Mask;
- KnownZero = ~KnownOne & Mask;
- return;
- }
- // Null is all-zeros.
- if (isa<ConstantPointerNull>(V)) {
- KnownOne.clear();
- KnownZero = Mask;
- return;
- }
- // The address of an aligned GlobalValue has trailing zeros.
- if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
- unsigned Align = GV->getAlignment();
- if (Align == 0 && TD && GV->getType()->getElementType()->isSized())
- Align = TD->getPrefTypeAlignment(GV->getType()->getElementType());
- if (Align > 0)
- KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
- CountTrailingZeros_32(Align));
- else
- KnownZero.clear();
- KnownOne.clear();
- return;
- }
-
- KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything.
-
- if (Depth == 6 || Mask == 0)
- return; // Limit search depth.
-
- User *I = dyn_cast<User>(V);
- if (!I) return;
-
- APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
- switch (getOpcode(I)) {
- default: break;
- case Instruction::And: {
- // If either the LHS or the RHS are Zero, the result is zero.
- ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
- APInt Mask2(Mask & ~KnownZero);
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
-
- // Output known-1 bits are only known if set in both the LHS & RHS.
- KnownOne &= KnownOne2;
- // Output known-0 are known to be clear if zero in either the LHS | RHS.
- KnownZero |= KnownZero2;
- return;
- }
- case Instruction::Or: {
- ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
- APInt Mask2(Mask & ~KnownOne);
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
-
- // Output known-0 bits are only known if clear in both the LHS & RHS.
- KnownZero &= KnownZero2;
- // Output known-1 are known to be set if set in either the LHS | RHS.
- KnownOne |= KnownOne2;
- return;
- }
- case Instruction::Xor: {
- ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
- ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
-
- // Output known-0 bits are known if clear or set in both the LHS & RHS.
- APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
- // Output known-1 are known to be set if set in only one of the LHS, RHS.
- KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
- KnownZero = KnownZeroOut;
- return;
- }
- case Instruction::Mul: {
- APInt Mask2 = APInt::getAllOnesValue(BitWidth);
- ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, Depth+1);
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
-
- // If low bits are zero in either operand, output low known-0 bits.
- // Also compute a conserative estimate for high known-0 bits.
- // More trickiness is possible, but this is sufficient for the
- // interesting case of alignment computation.
- KnownOne.clear();
- unsigned TrailZ = KnownZero.countTrailingOnes() +
- KnownZero2.countTrailingOnes();
- unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
- KnownZero2.countLeadingOnes(),
- BitWidth) - BitWidth;
-
- TrailZ = std::min(TrailZ, BitWidth);
- LeadZ = std::min(LeadZ, BitWidth);
- KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
- APInt::getHighBitsSet(BitWidth, LeadZ);
- KnownZero &= Mask;
- return;
- }
- case Instruction::UDiv: {
- // For the purposes of computing leading zeros we can conservatively
- // treat a udiv as a logical right shift by the power of 2 known to
- // be less than the denominator.
- APInt AllOnes = APInt::getAllOnesValue(BitWidth);
- ComputeMaskedBits(I->getOperand(0),
- AllOnes, KnownZero2, KnownOne2, Depth+1);
- unsigned LeadZ = KnownZero2.countLeadingOnes();
-
- KnownOne2.clear();
- KnownZero2.clear();
- ComputeMaskedBits(I->getOperand(1),
- AllOnes, KnownZero2, KnownOne2, Depth+1);
- unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
- if (RHSUnknownLeadingOnes != BitWidth)
- LeadZ = std::min(BitWidth,
- LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
-
- KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
- return;
- }
- case Instruction::Select:
- ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, Depth+1);
- ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
-
- // Only known if known in both the LHS and RHS.
- KnownOne &= KnownOne2;
- KnownZero &= KnownZero2;
- return;
- case Instruction::FPTrunc:
- case Instruction::FPExt:
- case Instruction::FPToUI:
- case Instruction::FPToSI:
- case Instruction::SIToFP:
- case Instruction::UIToFP:
- return; // Can't work with floating point.
- case Instruction::PtrToInt:
- case Instruction::IntToPtr:
- // We can't handle these if we don't know the pointer size.
- if (!TD) return;
- // FALL THROUGH and handle them the same as zext/trunc.
- case Instruction::ZExt:
- case Instruction::Trunc: {
- // Note that we handle pointer operands here because of inttoptr/ptrtoint
- // which fall through here.
- const Type *SrcTy = I->getOperand(0)->getType();
- uint32_t SrcBitWidth = TD ?
- TD->getTypeSizeInBits(SrcTy) :
- SrcTy->getPrimitiveSizeInBits();
- APInt MaskIn(Mask);
- MaskIn.zextOrTrunc(SrcBitWidth);
- KnownZero.zextOrTrunc(SrcBitWidth);
- KnownOne.zextOrTrunc(SrcBitWidth);
- ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
- KnownZero.zextOrTrunc(BitWidth);
- KnownOne.zextOrTrunc(BitWidth);
- // Any top bits are known to be zero.
- if (BitWidth > SrcBitWidth)
- KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
- return;
- }
- case Instruction::BitCast: {
- const Type *SrcTy = I->getOperand(0)->getType();
- if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) {
- ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
- return;
- }
- break;
- }
- case Instruction::SExt: {
- // Compute the bits in the result that are not present in the input.
- const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
- uint32_t SrcBitWidth = SrcTy->getBitWidth();
-
- APInt MaskIn(Mask);
- MaskIn.trunc(SrcBitWidth);
- KnownZero.trunc(SrcBitWidth);
- KnownOne.trunc(SrcBitWidth);
- ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- KnownZero.zext(BitWidth);
- KnownOne.zext(BitWidth);
-
- // If the sign bit of the input is known set or clear, then we know the
- // top bits of the result.
- if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
- KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
- else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
- KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
- return;
- }
- case Instruction::Shl:
- // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
- if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
- uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
- APInt Mask2(Mask.lshr(ShiftAmt));
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, Depth+1);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- KnownZero <<= ShiftAmt;
- KnownOne <<= ShiftAmt;
- KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
- return;
- }
- break;
- case Instruction::LShr:
- // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
- if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
- // Compute the new bits that are at the top now.
- uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
-
- // Unsigned shift right.
- APInt Mask2(Mask.shl(ShiftAmt));
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne,Depth+1);
- assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
- KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
- KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
- // high bits known zero.
- KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
- return;
- }
- break;
- case Instruction::AShr:
- // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
- if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
- // Compute the new bits that are at the top now.
- uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
-
- // Signed shift right.
- APInt Mask2(Mask.shl(ShiftAmt));
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne,Depth+1);
- assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
- KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
- KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
-
- APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
- if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
- KnownZero |= HighBits;
- else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
- KnownOne |= HighBits;
- return;
- }
- break;
- case Instruction::Sub: {
- if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) {
- // We know that the top bits of C-X are clear if X contains less bits
- // than C (i.e. no wrap-around can happen). For example, 20-X is
- // positive if we can prove that X is >= 0 and < 16.
- if (!CLHS->getValue().isNegative()) {
- unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
- // NLZ can't be BitWidth with no sign bit
- APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
- ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
- Depth+1);
-
- // If all of the MaskV bits are known to be zero, then we know the
- // output top bits are zero, because we now know that the output is
- // from [0-C].
- if ((KnownZero2 & MaskV) == MaskV) {
- unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
- // Top bits known zero.
- KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
- }
- }
- }
- }
- // fall through
- case Instruction::Add: {
- // Output known-0 bits are known if clear or set in both the low clear bits
- // common to both LHS & RHS. For example, 8+(X<<3) is known to have the
- // low 3 bits clear.
- APInt Mask2 = APInt::getLowBitsSet(BitWidth, Mask.countTrailingOnes());
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
- unsigned KnownZeroOut = KnownZero2.countTrailingOnes();
-
- ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, Depth+1);
- assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
- KnownZeroOut = std::min(KnownZeroOut,
- KnownZero2.countTrailingOnes());
-
- KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut);
- return;
- }
- case Instruction::SRem:
- if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
- APInt RA = Rem->getValue();
- if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
- APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
- APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
- ComputeMaskedBits(I->getOperand(0), Mask2,KnownZero2,KnownOne2,Depth+1);
-
- // The sign of a remainder is equal to the sign of the first
- // operand (zero being positive).
- if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
- KnownZero2 |= ~LowBits;
- else if (KnownOne2[BitWidth-1])
- KnownOne2 |= ~LowBits;
-
- KnownZero |= KnownZero2 & Mask;
- KnownOne |= KnownOne2 & Mask;
-
- assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
- }
- }
- break;
- case Instruction::URem: {
- if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
- APInt RA = Rem->getValue();
- if (RA.isPowerOf2()) {
- APInt LowBits = (RA - 1);
- APInt Mask2 = LowBits & Mask;
- KnownZero |= ~LowBits & Mask;
- ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne,Depth+1);
- assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
- break;
- }
- }
-
- // Since the result is less than or equal to either operand, any leading
- // zero bits in either operand must also exist in the result.
- APInt AllOnes = APInt::getAllOnesValue(BitWidth);
- ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne,
- Depth+1);
- ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
- Depth+1);
-
- uint32_t Leaders = std::max(KnownZero.countLeadingOnes(),
- KnownZero2.countLeadingOnes());
- KnownOne.clear();
- KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
- break;
- }
-
- case Instruction::Alloca:
- case Instruction::Malloc: {
- AllocationInst *AI = cast<AllocationInst>(V);
- unsigned Align = AI->getAlignment();
- if (Align == 0 && TD) {
- if (isa<AllocaInst>(AI))
- Align = TD->getPrefTypeAlignment(AI->getType()->getElementType());
- else if (isa<MallocInst>(AI)) {
- // Malloc returns maximally aligned memory.
- Align = TD->getABITypeAlignment(AI->getType()->getElementType());
- Align =
- std::max(Align,
- (unsigned)TD->getABITypeAlignment(Type::DoubleTy));
- Align =
- std::max(Align,
- (unsigned)TD->getABITypeAlignment(Type::Int64Ty));
- }
- }
-
- if (Align > 0)
- KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
- CountTrailingZeros_32(Align));
- break;
- }
- case Instruction::GetElementPtr: {
- // Analyze all of the subscripts of this getelementptr instruction
- // to determine if we can prove known low zero bits.
- APInt LocalMask = APInt::getAllOnesValue(BitWidth);
- APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
- ComputeMaskedBits(I->getOperand(0), LocalMask,
- LocalKnownZero, LocalKnownOne, Depth+1);
- unsigned TrailZ = LocalKnownZero.countTrailingOnes();
-
- gep_type_iterator GTI = gep_type_begin(I);
- for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
- Value *Index = I->getOperand(i);
- if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
- // Handle struct member offset arithmetic.
- if (!TD) return;
- const StructLayout *SL = TD->getStructLayout(STy);
- unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
- uint64_t Offset = SL->getElementOffset(Idx);
- TrailZ = std::min(TrailZ,
- CountTrailingZeros_64(Offset));
- } else {
- // Handle array index arithmetic.
- const Type *IndexedTy = GTI.getIndexedType();
- if (!IndexedTy->isSized()) return;
- unsigned GEPOpiBits = Index->getType()->getPrimitiveSizeInBits();
- uint64_t TypeSize = TD ? TD->getABITypeSize(IndexedTy) : 1;
- LocalMask = APInt::getAllOnesValue(GEPOpiBits);
- LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
- ComputeMaskedBits(Index, LocalMask,
- LocalKnownZero, LocalKnownOne, Depth+1);
- TrailZ = std::min(TrailZ,
- CountTrailingZeros_64(TypeSize) +
- LocalKnownZero.countTrailingOnes());
- }
- }
-
- KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
- break;
- }
- case Instruction::PHI: {
- PHINode *P = cast<PHINode>(I);
- // Handle the case of a simple two-predecessor recurrence PHI.
- // There's a lot more that could theoretically be done here, but
- // this is sufficient to catch some interesting cases.
- if (P->getNumIncomingValues() == 2) {
- for (unsigned i = 0; i != 2; ++i) {
- Value *L = P->getIncomingValue(i);
- Value *R = P->getIncomingValue(!i);
- User *LU = dyn_cast<User>(L);
- if (!LU)
- continue;
- unsigned Opcode = getOpcode(LU);
- // Check for operations that have the property that if
- // both their operands have low zero bits, the result
- // will have low zero bits.
- if (Opcode == Instruction::Add ||
- Opcode == Instruction::Sub ||
- Opcode == Instruction::And ||
- Opcode == Instruction::Or ||
- Opcode == Instruction::Mul) {
- Value *LL = LU->getOperand(0);
- Value *LR = LU->getOperand(1);
- // Find a recurrence.
- if (LL == I)
- L = LR;
- else if (LR == I)
- L = LL;
- else
- break;
- // Ok, we have a PHI of the form L op= R. Check for low
- // zero bits.
- APInt Mask2 = APInt::getAllOnesValue(BitWidth);
- ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, Depth+1);
- Mask2 = APInt::getLowBitsSet(BitWidth,
- KnownZero2.countTrailingOnes());
- KnownOne2.clear();
- KnownZero2.clear();
- ComputeMaskedBits(L, Mask2, KnownZero2, KnownOne2, Depth+1);
- KnownZero = Mask &
- APInt::getLowBitsSet(BitWidth,
- KnownZero2.countTrailingOnes());
- break;
- }
- }
- }
- break;
- }
- case Instruction::Call:
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
- switch (II->getIntrinsicID()) {
- default: break;
- case Intrinsic::ctpop:
- case Intrinsic::ctlz:
- case Intrinsic::cttz: {
- unsigned LowBits = Log2_32(BitWidth)+1;
- KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
- break;
- }
- }
- }
- break;
- }
-}
-
-/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
-/// this predicate to simplify operations downstream. Mask is known to be zero
-/// for bits that V cannot have.
-bool InstCombiner::MaskedValueIsZero(Value *V, const APInt& Mask,
- unsigned Depth) {
- APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
- ComputeMaskedBits(V, Mask, KnownZero, KnownOne, Depth);
- assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
- return (KnownZero & Mask) == Mask;
-}
/// ShrinkDemandedConstant - Check to see if the specified operand of the
/// specified instruction is a constant integer. If so, check to see if there
return MadeChange ? I : 0;
}
-/// ComputeNumSignBits - Return the number of times the sign bit of the
-/// register is replicated into the other bits. We know that at least 1 bit
-/// is always equal to the sign bit (itself), but other cases can give us
-/// information. For example, immediately after an "ashr X, 2", we know that
-/// the top 3 bits are all equal to each other, so we return 3.
-///
-unsigned InstCombiner::ComputeNumSignBits(Value *V, unsigned Depth) const{
- const IntegerType *Ty = cast<IntegerType>(V->getType());
- unsigned TyBits = Ty->getBitWidth();
- unsigned Tmp, Tmp2;
- unsigned FirstAnswer = 1;
-
- if (Depth == 6)
- return 1; // Limit search depth.
-
- User *U = dyn_cast<User>(V);
- switch (getOpcode(V)) {
- default: break;
- case Instruction::SExt:
- Tmp = TyBits-cast<IntegerType>(U->getOperand(0)->getType())->getBitWidth();
- return ComputeNumSignBits(U->getOperand(0), Depth+1) + Tmp;
-
- case Instruction::AShr:
- Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
- // ashr X, C -> adds C sign bits.
- if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
- Tmp += C->getZExtValue();
- if (Tmp > TyBits) Tmp = TyBits;
- }
- return Tmp;
- case Instruction::Shl:
- if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
- // shl destroys sign bits.
- Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
- if (C->getZExtValue() >= TyBits || // Bad shift.
- C->getZExtValue() >= Tmp) break; // Shifted all sign bits out.
- return Tmp - C->getZExtValue();
- }
- break;
- case Instruction::And:
- case Instruction::Or:
- case Instruction::Xor: // NOT is handled here.
- // Logical binary ops preserve the number of sign bits at the worst.
- Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
- if (Tmp != 1) {
- Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
- FirstAnswer = std::min(Tmp, Tmp2);
- // We computed what we know about the sign bits as our first
- // answer. Now proceed to the generic code that uses
- // ComputeMaskedBits, and pick whichever answer is better.
- }
- break;
-
- case Instruction::Select:
- Tmp = ComputeNumSignBits(U->getOperand(1), Depth+1);
- if (Tmp == 1) return 1; // Early out.
- Tmp2 = ComputeNumSignBits(U->getOperand(2), Depth+1);
- return std::min(Tmp, Tmp2);
-
- case Instruction::Add:
- // Add can have at most one carry bit. Thus we know that the output
- // is, at worst, one more bit than the inputs.
- Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
- if (Tmp == 1) return 1; // Early out.
-
- // Special case decrementing a value (ADD X, -1):
- if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(0)))
- if (CRHS->isAllOnesValue()) {
- APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
- APInt Mask = APInt::getAllOnesValue(TyBits);
- ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
-
- // If the input is known to be 0 or 1, the output is 0/-1, which is all
- // sign bits set.
- if ((KnownZero | APInt(TyBits, 1)) == Mask)
- return TyBits;
-
- // If we are subtracting one from a positive number, there is no carry
- // out of the result.
- if (KnownZero.isNegative())
- return Tmp;
- }
-
- Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
- if (Tmp2 == 1) return 1;
- return std::min(Tmp, Tmp2)-1;
- break;
-
- case Instruction::Sub:
- Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
- if (Tmp2 == 1) return 1;
-
- // Handle NEG.
- if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0)))
- if (CLHS->isNullValue()) {
- APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
- APInt Mask = APInt::getAllOnesValue(TyBits);
- ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
- // If the input is known to be 0 or 1, the output is 0/-1, which is all
- // sign bits set.
- if ((KnownZero | APInt(TyBits, 1)) == Mask)
- return TyBits;
-
- // If the input is known to be positive (the sign bit is known clear),
- // the output of the NEG has the same number of sign bits as the input.
- if (KnownZero.isNegative())
- return Tmp2;
-
- // Otherwise, we treat this like a SUB.
- }
-
- // Sub can have at most one carry bit. Thus we know that the output
- // is, at worst, one more bit than the inputs.
- Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
- if (Tmp == 1) return 1; // Early out.
- return std::min(Tmp, Tmp2)-1;
- break;
- case Instruction::Trunc:
- // FIXME: it's tricky to do anything useful for this, but it is an important
- // case for targets like X86.
- break;
- }
-
- // Finally, if we can prove that the top bits of the result are 0's or 1's,
- // use this information.
- APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
- APInt Mask = APInt::getAllOnesValue(TyBits);
- ComputeMaskedBits(V, Mask, KnownZero, KnownOne, Depth);
-
- if (KnownZero.isNegative()) { // sign bit is 0
- Mask = KnownZero;
- } else if (KnownOne.isNegative()) { // sign bit is 1;
- Mask = KnownOne;
- } else {
- // Nothing known.
- return FirstAnswer;
- }
-
- // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
- // the number of identical bits in the top of the input value.
- Mask = ~Mask;
- Mask <<= Mask.getBitWidth()-TyBits;
- // Return # leading zeros. We use 'min' here in case Val was zero before
- // shifting. We don't want to return '64' as for an i32 "0".
- return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
-}
-
/// AssociativeOpt - Perform an optimization on an associative operator. This
/// function is designed to check a chain of associative operators for a
projects / oota-llvm.git / commitdiff