mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-17 05:29:24 +00:00
move ComputeMaskedBits, MaskedValueIsZero, and ComputeNumSignBits
out of instcombine into a new file in libanalysis. This also teaches ComputeNumSignBits about the number of sign bits in a constantint. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51863 91177308-0d34-0410-b5e6-96231b3b80d8
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48
include/llvm/Analysis/ValueTracking.h
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48
include/llvm/Analysis/ValueTracking.h
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@ -0,0 +1,48 @@
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//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains routines that help analyze properties that chains of
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// computations have.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_VALUETRACKING_H
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#define LLVM_ANALYSIS_VALUETRACKING_H
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namespace llvm {
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class Value;
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class APInt;
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class TargetData;
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/// ComputeMaskedBits - Determine which of the bits specified in Mask are
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/// known to be either zero or one and return them in the KnownZero/KnownOne
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/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
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/// processing.
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void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
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APInt &KnownOne, TargetData *TD = 0,
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unsigned Depth = 0);
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bool MaskedValueIsZero(Value *V, const APInt &Mask,
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TargetData *TD = 0, unsigned Depth = 0);
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/// ComputeNumSignBits - Return the number of times the sign bit of the
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/// register is replicated into the other bits. We know that at least 1 bit
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/// is always equal to the sign bit (itself), but other cases can give us
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/// information. For example, immediately after an "ashr X, 2", we know that
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/// the top 3 bits are all equal to each other, so we return 3.
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///
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/// 'Op' must have a scalar integer type.
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///
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unsigned ComputeNumSignBits(Value *Op, TargetData *TD = 0,
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unsigned Depth = 0);
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} // end namespace llvm
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#endif
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709
lib/Analysis/ValueTracking.cpp
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709
lib/Analysis/ValueTracking.cpp
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//===- ValueTracking.cpp - Walk computations to compute properties --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains routines that help analyze properties that chains of
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// computations have.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/MathExtras.h"
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using namespace llvm;
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/// getOpcode - If this is an Instruction or a ConstantExpr, return the
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/// opcode value. Otherwise return UserOp1.
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static unsigned getOpcode(const Value *V) {
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if (const Instruction *I = dyn_cast<Instruction>(V))
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return I->getOpcode();
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if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
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return CE->getOpcode();
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// Use UserOp1 to mean there's no opcode.
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return Instruction::UserOp1;
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}
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/// ComputeMaskedBits - Determine which of the bits specified in Mask are
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/// known to be either zero or one and return them in the KnownZero/KnownOne
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/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
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/// processing.
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/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
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/// we cannot optimize based on the assumption that it is zero without changing
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/// it to be an explicit zero. If we don't change it to zero, other code could
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/// optimized based on the contradictory assumption that it is non-zero.
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/// Because instcombine aggressively folds operations with undef args anyway,
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/// this won't lose us code quality.
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void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
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APInt &KnownZero, APInt &KnownOne,
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TargetData *TD, unsigned Depth) {
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assert(V && "No Value?");
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assert(Depth <= 6 && "Limit Search Depth");
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uint32_t BitWidth = Mask.getBitWidth();
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assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) &&
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"Not integer or pointer type!");
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assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) &&
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(!isa<IntegerType>(V->getType()) ||
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V->getType()->getPrimitiveSizeInBits() == BitWidth) &&
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KnownZero.getBitWidth() == BitWidth &&
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KnownOne.getBitWidth() == BitWidth &&
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"V, Mask, KnownOne and KnownZero should have same BitWidth");
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if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
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// We know all of the bits for a constant!
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KnownOne = CI->getValue() & Mask;
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KnownZero = ~KnownOne & Mask;
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return;
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}
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// Null is all-zeros.
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if (isa<ConstantPointerNull>(V)) {
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KnownOne.clear();
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KnownZero = Mask;
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return;
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}
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// The address of an aligned GlobalValue has trailing zeros.
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if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
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unsigned Align = GV->getAlignment();
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if (Align == 0 && TD && GV->getType()->getElementType()->isSized())
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Align = TD->getPrefTypeAlignment(GV->getType()->getElementType());
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if (Align > 0)
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KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
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CountTrailingZeros_32(Align));
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else
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KnownZero.clear();
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KnownOne.clear();
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return;
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}
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KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything.
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if (Depth == 6 || Mask == 0)
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return; // Limit search depth.
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User *I = dyn_cast<User>(V);
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if (!I) return;
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APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
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switch (getOpcode(I)) {
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default: break;
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case Instruction::And: {
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// If either the LHS or the RHS are Zero, the result is zero.
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
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APInt Mask2(Mask & ~KnownZero);
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Output known-1 bits are only known if set in both the LHS & RHS.
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KnownOne &= KnownOne2;
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// Output known-0 are known to be clear if zero in either the LHS | RHS.
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KnownZero |= KnownZero2;
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return;
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}
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case Instruction::Or: {
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
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APInt Mask2(Mask & ~KnownOne);
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Output known-0 bits are only known if clear in both the LHS & RHS.
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KnownZero &= KnownZero2;
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// Output known-1 are known to be set if set in either the LHS | RHS.
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KnownOne |= KnownOne2;
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return;
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}
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case Instruction::Xor: {
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
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ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Output known-0 bits are known if clear or set in both the LHS & RHS.
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APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
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// Output known-1 are known to be set if set in only one of the LHS, RHS.
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KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
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KnownZero = KnownZeroOut;
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return;
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}
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case Instruction::Mul: {
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APInt Mask2 = APInt::getAllOnesValue(BitWidth);
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ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1);
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// If low bits are zero in either operand, output low known-0 bits.
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// Also compute a conserative estimate for high known-0 bits.
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// More trickiness is possible, but this is sufficient for the
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// interesting case of alignment computation.
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KnownOne.clear();
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unsigned TrailZ = KnownZero.countTrailingOnes() +
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KnownZero2.countTrailingOnes();
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unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
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KnownZero2.countLeadingOnes(),
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BitWidth) - BitWidth;
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TrailZ = std::min(TrailZ, BitWidth);
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LeadZ = std::min(LeadZ, BitWidth);
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KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
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APInt::getHighBitsSet(BitWidth, LeadZ);
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KnownZero &= Mask;
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return;
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}
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case Instruction::UDiv: {
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// For the purposes of computing leading zeros we can conservatively
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// treat a udiv as a logical right shift by the power of 2 known to
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// be less than the denominator.
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APInt AllOnes = APInt::getAllOnesValue(BitWidth);
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ComputeMaskedBits(I->getOperand(0),
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AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
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unsigned LeadZ = KnownZero2.countLeadingOnes();
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KnownOne2.clear();
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KnownZero2.clear();
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ComputeMaskedBits(I->getOperand(1),
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AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
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unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
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if (RHSUnknownLeadingOnes != BitWidth)
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LeadZ = std::min(BitWidth,
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LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
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KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
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return;
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}
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case Instruction::Select:
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ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1);
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Only known if known in both the LHS and RHS.
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KnownOne &= KnownOne2;
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KnownZero &= KnownZero2;
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return;
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case Instruction::FPTrunc:
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case Instruction::FPExt:
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case Instruction::FPToUI:
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case Instruction::FPToSI:
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case Instruction::SIToFP:
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case Instruction::UIToFP:
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return; // Can't work with floating point.
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case Instruction::PtrToInt:
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case Instruction::IntToPtr:
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// We can't handle these if we don't know the pointer size.
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if (!TD) return;
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// FALL THROUGH and handle them the same as zext/trunc.
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case Instruction::ZExt:
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case Instruction::Trunc: {
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// Note that we handle pointer operands here because of inttoptr/ptrtoint
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// which fall through here.
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const Type *SrcTy = I->getOperand(0)->getType();
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uint32_t SrcBitWidth = TD ?
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TD->getTypeSizeInBits(SrcTy) :
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SrcTy->getPrimitiveSizeInBits();
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APInt MaskIn(Mask);
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MaskIn.zextOrTrunc(SrcBitWidth);
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KnownZero.zextOrTrunc(SrcBitWidth);
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KnownOne.zextOrTrunc(SrcBitWidth);
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ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
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Depth+1);
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KnownZero.zextOrTrunc(BitWidth);
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KnownOne.zextOrTrunc(BitWidth);
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// Any top bits are known to be zero.
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if (BitWidth > SrcBitWidth)
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KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
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return;
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}
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case Instruction::BitCast: {
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const Type *SrcTy = I->getOperand(0)->getType();
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if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) {
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ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD,
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Depth+1);
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return;
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}
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break;
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}
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case Instruction::SExt: {
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// Compute the bits in the result that are not present in the input.
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const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
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uint32_t SrcBitWidth = SrcTy->getBitWidth();
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APInt MaskIn(Mask);
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MaskIn.trunc(SrcBitWidth);
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KnownZero.trunc(SrcBitWidth);
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KnownOne.trunc(SrcBitWidth);
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ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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KnownZero.zext(BitWidth);
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KnownOne.zext(BitWidth);
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// If the sign bit of the input is known set or clear, then we know the
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// top bits of the result.
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if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
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KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
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else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
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KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
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return;
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}
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case Instruction::Shl:
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// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
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if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
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uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
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APInt Mask2(Mask.lshr(ShiftAmt));
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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KnownZero <<= ShiftAmt;
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KnownOne <<= ShiftAmt;
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KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
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return;
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}
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break;
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case Instruction::LShr:
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// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
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if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
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// Compute the new bits that are at the top now.
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uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
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// Unsigned shift right.
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APInt Mask2(Mask.shl(ShiftAmt));
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
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KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
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KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
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// high bits known zero.
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KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
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return;
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}
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break;
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case Instruction::AShr:
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// (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
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if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
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// Compute the new bits that are at the top now.
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uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
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// Signed shift right.
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APInt Mask2(Mask.shl(ShiftAmt));
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
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KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
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KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
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APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
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if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
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KnownZero |= HighBits;
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else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
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KnownOne |= HighBits;
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return;
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}
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break;
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case Instruction::Sub: {
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if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) {
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// We know that the top bits of C-X are clear if X contains less bits
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// than C (i.e. no wrap-around can happen). For example, 20-X is
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// positive if we can prove that X is >= 0 and < 16.
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if (!CLHS->getValue().isNegative()) {
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unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
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// NLZ can't be BitWidth with no sign bit
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APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
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ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
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TD, Depth+1);
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// If all of the MaskV bits are known to be zero, then we know the
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// output top bits are zero, because we now know that the output is
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// from [0-C].
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if ((KnownZero2 & MaskV) == MaskV) {
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unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
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// Top bits known zero.
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KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
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}
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}
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}
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}
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// fall through
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case Instruction::Add: {
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// Output known-0 bits are known if clear or set in both the low clear bits
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// common to both LHS & RHS. For example, 8+(X<<3) is known to have the
|
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// low 3 bits clear.
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APInt Mask2 = APInt::getLowBitsSet(BitWidth, Mask.countTrailingOnes());
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
|
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Depth+1);
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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unsigned KnownZeroOut = KnownZero2.countTrailingOnes();
|
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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()));
|
||||
}
|
@ -40,6 +40,7 @@
|
||||
#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"
|
||||
@ -324,6 +325,19 @@ namespace {
|
||||
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
|
||||
/// InsertBefore instruction. This is specialized a bit to avoid inserting
|
||||
@ -378,10 +392,6 @@ namespace {
|
||||
|
||||
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);
|
||||
@ -661,506 +671,6 @@ static bool MultiplyOverflows(ConstantInt *C1, ConstantInt *C2, bool sign) {
|
||||
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
|
||||
@ -2069,153 +1579,6 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, uint64_t DemandedElts,
|
||||
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
|
||||
|
Loading…
Reference in New Issue
Block a user