forked from OSchip/llvm-project
1308 lines
53 KiB
C++
1308 lines
53 KiB
C++
//===- InstCombineShifts.cpp ----------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the visitShl, visitLShr, and visitAShr functions.
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//
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//===----------------------------------------------------------------------===//
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#include "InstCombineInternal.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/PatternMatch.h"
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using namespace llvm;
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using namespace PatternMatch;
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#define DEBUG_TYPE "instcombine"
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// Given pattern:
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// (x shiftopcode Q) shiftopcode K
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// we should rewrite it as
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// x shiftopcode (Q+K) iff (Q+K) u< bitwidth(x)
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// This is valid for any shift, but they must be identical.
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//
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// AnalyzeForSignBitExtraction indicates that we will only analyze whether this
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// pattern has any 2 right-shifts that sum to 1 less than original bit width.
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Value *InstCombiner::reassociateShiftAmtsOfTwoSameDirectionShifts(
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BinaryOperator *Sh0, const SimplifyQuery &SQ,
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bool AnalyzeForSignBitExtraction) {
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// Look for a shift of some instruction, ignore zext of shift amount if any.
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Instruction *Sh0Op0;
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Value *ShAmt0;
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if (!match(Sh0,
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m_Shift(m_Instruction(Sh0Op0), m_ZExtOrSelf(m_Value(ShAmt0)))))
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return nullptr;
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// If there is a truncation between the two shifts, we must make note of it
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// and look through it. The truncation imposes additional constraints on the
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// transform.
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Instruction *Sh1;
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Value *Trunc = nullptr;
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match(Sh0Op0,
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m_CombineOr(m_CombineAnd(m_Trunc(m_Instruction(Sh1)), m_Value(Trunc)),
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m_Instruction(Sh1)));
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// Inner shift: (x shiftopcode ShAmt1)
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// Like with other shift, ignore zext of shift amount if any.
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Value *X, *ShAmt1;
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if (!match(Sh1, m_Shift(m_Value(X), m_ZExtOrSelf(m_Value(ShAmt1)))))
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return nullptr;
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// We have two shift amounts from two different shifts. The types of those
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// shift amounts may not match. If that's the case let's bailout now..
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if (ShAmt0->getType() != ShAmt1->getType())
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return nullptr;
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// We are only looking for signbit extraction if we have two right shifts.
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bool HadTwoRightShifts = match(Sh0, m_Shr(m_Value(), m_Value())) &&
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match(Sh1, m_Shr(m_Value(), m_Value()));
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// ... and if it's not two right-shifts, we know the answer already.
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if (AnalyzeForSignBitExtraction && !HadTwoRightShifts)
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return nullptr;
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// The shift opcodes must be identical, unless we are just checking whether
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// this pattern can be interpreted as a sign-bit-extraction.
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Instruction::BinaryOps ShiftOpcode = Sh0->getOpcode();
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bool IdenticalShOpcodes = Sh0->getOpcode() == Sh1->getOpcode();
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if (!IdenticalShOpcodes && !AnalyzeForSignBitExtraction)
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return nullptr;
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// If we saw truncation, we'll need to produce extra instruction,
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// and for that one of the operands of the shift must be one-use,
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// unless of course we don't actually plan to produce any instructions here.
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if (Trunc && !AnalyzeForSignBitExtraction &&
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!match(Sh0, m_c_BinOp(m_OneUse(m_Value()), m_Value())))
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return nullptr;
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// Can we fold (ShAmt0+ShAmt1) ?
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auto *NewShAmt = dyn_cast_or_null<Constant>(
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SimplifyAddInst(ShAmt0, ShAmt1, /*isNSW=*/false, /*isNUW=*/false,
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SQ.getWithInstruction(Sh0)));
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if (!NewShAmt)
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return nullptr; // Did not simplify.
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unsigned NewShAmtBitWidth = NewShAmt->getType()->getScalarSizeInBits();
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unsigned XBitWidth = X->getType()->getScalarSizeInBits();
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// Is the new shift amount smaller than the bit width of inner/new shift?
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if (!match(NewShAmt, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_ULT,
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APInt(NewShAmtBitWidth, XBitWidth))))
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return nullptr; // FIXME: could perform constant-folding.
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// If there was a truncation, and we have a right-shift, we can only fold if
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// we are left with the original sign bit. Likewise, if we were just checking
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// that this is a sighbit extraction, this is the place to check it.
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// FIXME: zero shift amount is also legal here, but we can't *easily* check
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// more than one predicate so it's not really worth it.
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if (HadTwoRightShifts && (Trunc || AnalyzeForSignBitExtraction)) {
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// If it's not a sign bit extraction, then we're done.
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if (!match(NewShAmt,
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m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_EQ,
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APInt(NewShAmtBitWidth, XBitWidth - 1))))
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return nullptr;
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// If it is, and that was the question, return the base value.
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if (AnalyzeForSignBitExtraction)
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return X;
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}
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assert(IdenticalShOpcodes && "Should not get here with different shifts.");
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// All good, we can do this fold.
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NewShAmt = ConstantExpr::getZExtOrBitCast(NewShAmt, X->getType());
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BinaryOperator *NewShift = BinaryOperator::Create(ShiftOpcode, X, NewShAmt);
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// The flags can only be propagated if there wasn't a trunc.
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if (!Trunc) {
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// If the pattern did not involve trunc, and both of the original shifts
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// had the same flag set, preserve the flag.
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if (ShiftOpcode == Instruction::BinaryOps::Shl) {
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NewShift->setHasNoUnsignedWrap(Sh0->hasNoUnsignedWrap() &&
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Sh1->hasNoUnsignedWrap());
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NewShift->setHasNoSignedWrap(Sh0->hasNoSignedWrap() &&
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Sh1->hasNoSignedWrap());
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} else {
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NewShift->setIsExact(Sh0->isExact() && Sh1->isExact());
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}
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}
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Instruction *Ret = NewShift;
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if (Trunc) {
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Builder.Insert(NewShift);
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Ret = CastInst::Create(Instruction::Trunc, NewShift, Sh0->getType());
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}
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return Ret;
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}
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// If we have some pattern that leaves only some low bits set, and then performs
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// left-shift of those bits, if none of the bits that are left after the final
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// shift are modified by the mask, we can omit the mask.
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//
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// There are many variants to this pattern:
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// a) (x & ((1 << MaskShAmt) - 1)) << ShiftShAmt
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// b) (x & (~(-1 << MaskShAmt))) << ShiftShAmt
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// c) (x & (-1 >> MaskShAmt)) << ShiftShAmt
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// d) (x & ((-1 << MaskShAmt) >> MaskShAmt)) << ShiftShAmt
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// e) ((x << MaskShAmt) l>> MaskShAmt) << ShiftShAmt
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// f) ((x << MaskShAmt) a>> MaskShAmt) << ShiftShAmt
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// All these patterns can be simplified to just:
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// x << ShiftShAmt
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// iff:
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// a,b) (MaskShAmt+ShiftShAmt) u>= bitwidth(x)
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// c,d,e,f) (ShiftShAmt-MaskShAmt) s>= 0 (i.e. ShiftShAmt u>= MaskShAmt)
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static Instruction *
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dropRedundantMaskingOfLeftShiftInput(BinaryOperator *OuterShift,
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const SimplifyQuery &Q,
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InstCombiner::BuilderTy &Builder) {
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assert(OuterShift->getOpcode() == Instruction::BinaryOps::Shl &&
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"The input must be 'shl'!");
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Value *Masked, *ShiftShAmt;
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match(OuterShift,
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m_Shift(m_Value(Masked), m_ZExtOrSelf(m_Value(ShiftShAmt))));
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// *If* there is a truncation between an outer shift and a possibly-mask,
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// then said truncation *must* be one-use, else we can't perform the fold.
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Value *Trunc;
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if (match(Masked, m_CombineAnd(m_Trunc(m_Value(Masked)), m_Value(Trunc))) &&
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!Trunc->hasOneUse())
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return nullptr;
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Type *NarrowestTy = OuterShift->getType();
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Type *WidestTy = Masked->getType();
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bool HadTrunc = WidestTy != NarrowestTy;
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// The mask must be computed in a type twice as wide to ensure
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// that no bits are lost if the sum-of-shifts is wider than the base type.
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Type *ExtendedTy = WidestTy->getExtendedType();
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Value *MaskShAmt;
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// ((1 << MaskShAmt) - 1)
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auto MaskA = m_Add(m_Shl(m_One(), m_Value(MaskShAmt)), m_AllOnes());
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// (~(-1 << maskNbits))
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auto MaskB = m_Xor(m_Shl(m_AllOnes(), m_Value(MaskShAmt)), m_AllOnes());
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// (-1 >> MaskShAmt)
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auto MaskC = m_Shr(m_AllOnes(), m_Value(MaskShAmt));
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// ((-1 << MaskShAmt) >> MaskShAmt)
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auto MaskD =
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m_Shr(m_Shl(m_AllOnes(), m_Value(MaskShAmt)), m_Deferred(MaskShAmt));
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Value *X;
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Constant *NewMask;
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if (match(Masked, m_c_And(m_CombineOr(MaskA, MaskB), m_Value(X)))) {
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// Peek through an optional zext of the shift amount.
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match(MaskShAmt, m_ZExtOrSelf(m_Value(MaskShAmt)));
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// We have two shift amounts from two different shifts. The types of those
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// shift amounts may not match. If that's the case let's bailout now.
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if (MaskShAmt->getType() != ShiftShAmt->getType())
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return nullptr;
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// Can we simplify (MaskShAmt+ShiftShAmt) ?
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auto *SumOfShAmts = dyn_cast_or_null<Constant>(SimplifyAddInst(
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MaskShAmt, ShiftShAmt, /*IsNSW=*/false, /*IsNUW=*/false, Q));
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if (!SumOfShAmts)
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return nullptr; // Did not simplify.
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// In this pattern SumOfShAmts correlates with the number of low bits
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// that shall remain in the root value (OuterShift).
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// An extend of an undef value becomes zero because the high bits are never
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// completely unknown. Replace the the `undef` shift amounts with final
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// shift bitwidth to ensure that the value remains undef when creating the
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// subsequent shift op.
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SumOfShAmts = Constant::replaceUndefsWith(
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SumOfShAmts, ConstantInt::get(SumOfShAmts->getType()->getScalarType(),
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ExtendedTy->getScalarSizeInBits()));
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auto *ExtendedSumOfShAmts = ConstantExpr::getZExt(SumOfShAmts, ExtendedTy);
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// And compute the mask as usual: ~(-1 << (SumOfShAmts))
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auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(ExtendedTy);
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auto *ExtendedInvertedMask =
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ConstantExpr::getShl(ExtendedAllOnes, ExtendedSumOfShAmts);
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NewMask = ConstantExpr::getNot(ExtendedInvertedMask);
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} else if (match(Masked, m_c_And(m_CombineOr(MaskC, MaskD), m_Value(X))) ||
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match(Masked, m_Shr(m_Shl(m_Value(X), m_Value(MaskShAmt)),
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m_Deferred(MaskShAmt)))) {
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// Peek through an optional zext of the shift amount.
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match(MaskShAmt, m_ZExtOrSelf(m_Value(MaskShAmt)));
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// We have two shift amounts from two different shifts. The types of those
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// shift amounts may not match. If that's the case let's bailout now.
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if (MaskShAmt->getType() != ShiftShAmt->getType())
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return nullptr;
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// Can we simplify (ShiftShAmt-MaskShAmt) ?
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auto *ShAmtsDiff = dyn_cast_or_null<Constant>(SimplifySubInst(
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ShiftShAmt, MaskShAmt, /*IsNSW=*/false, /*IsNUW=*/false, Q));
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if (!ShAmtsDiff)
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return nullptr; // Did not simplify.
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// In this pattern ShAmtsDiff correlates with the number of high bits that
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// shall be unset in the root value (OuterShift).
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// An extend of an undef value becomes zero because the high bits are never
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// completely unknown. Replace the the `undef` shift amounts with negated
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// bitwidth of innermost shift to ensure that the value remains undef when
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// creating the subsequent shift op.
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unsigned WidestTyBitWidth = WidestTy->getScalarSizeInBits();
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ShAmtsDiff = Constant::replaceUndefsWith(
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ShAmtsDiff, ConstantInt::get(ShAmtsDiff->getType()->getScalarType(),
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-WidestTyBitWidth));
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auto *ExtendedNumHighBitsToClear = ConstantExpr::getZExt(
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ConstantExpr::getSub(ConstantInt::get(ShAmtsDiff->getType(),
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WidestTyBitWidth,
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/*isSigned=*/false),
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ShAmtsDiff),
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ExtendedTy);
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// And compute the mask as usual: (-1 l>> (NumHighBitsToClear))
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auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(ExtendedTy);
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NewMask =
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ConstantExpr::getLShr(ExtendedAllOnes, ExtendedNumHighBitsToClear);
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} else
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return nullptr; // Don't know anything about this pattern.
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NewMask = ConstantExpr::getTrunc(NewMask, NarrowestTy);
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// Does this mask has any unset bits? If not then we can just not apply it.
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bool NeedMask = !match(NewMask, m_AllOnes());
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// If we need to apply a mask, there are several more restrictions we have.
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if (NeedMask) {
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// The old masking instruction must go away.
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if (!Masked->hasOneUse())
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return nullptr;
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// The original "masking" instruction must not have been`ashr`.
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if (match(Masked, m_AShr(m_Value(), m_Value())))
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return nullptr;
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}
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// If we need to apply truncation, let's do it first, since we can.
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// We have already ensured that the old truncation will go away.
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if (HadTrunc)
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X = Builder.CreateTrunc(X, NarrowestTy);
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// No 'NUW'/'NSW'! We no longer know that we won't shift-out non-0 bits.
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// We didn't change the Type of this outermost shift, so we can just do it.
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auto *NewShift = BinaryOperator::Create(OuterShift->getOpcode(), X,
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OuterShift->getOperand(1));
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if (!NeedMask)
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return NewShift;
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Builder.Insert(NewShift);
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return BinaryOperator::Create(Instruction::And, NewShift, NewMask);
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}
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/// If we have a shift-by-constant of a bitwise logic op that itself has a
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/// shift-by-constant operand with identical opcode, we may be able to convert
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/// that into 2 independent shifts followed by the logic op. This eliminates a
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/// a use of an intermediate value (reduces dependency chain).
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static Instruction *foldShiftOfShiftedLogic(BinaryOperator &I,
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InstCombiner::BuilderTy &Builder) {
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assert(I.isShift() && "Expected a shift as input");
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auto *LogicInst = dyn_cast<BinaryOperator>(I.getOperand(0));
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if (!LogicInst || !LogicInst->isBitwiseLogicOp() || !LogicInst->hasOneUse())
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return nullptr;
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const APInt *C0, *C1;
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if (!match(I.getOperand(1), m_APInt(C1)))
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return nullptr;
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Instruction::BinaryOps ShiftOpcode = I.getOpcode();
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Type *Ty = I.getType();
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// Find a matching one-use shift by constant. The fold is not valid if the sum
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// of the shift values equals or exceeds bitwidth.
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// TODO: Remove the one-use check if the other logic operand (Y) is constant.
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Value *X, *Y;
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auto matchFirstShift = [&](Value *V) {
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return !isa<ConstantExpr>(V) &&
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match(V, m_OneUse(m_Shift(m_Value(X), m_APInt(C0)))) &&
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cast<BinaryOperator>(V)->getOpcode() == ShiftOpcode &&
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(*C0 + *C1).ult(Ty->getScalarSizeInBits());
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};
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// Logic ops are commutative, so check each operand for a match.
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if (matchFirstShift(LogicInst->getOperand(0)))
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Y = LogicInst->getOperand(1);
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else if (matchFirstShift(LogicInst->getOperand(1)))
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Y = LogicInst->getOperand(0);
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else
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return nullptr;
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// shift (logic (shift X, C0), Y), C1 -> logic (shift X, C0+C1), (shift Y, C1)
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Constant *ShiftSumC = ConstantInt::get(Ty, *C0 + *C1);
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Value *NewShift1 = Builder.CreateBinOp(ShiftOpcode, X, ShiftSumC);
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Value *NewShift2 = Builder.CreateBinOp(ShiftOpcode, Y, I.getOperand(1));
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return BinaryOperator::Create(LogicInst->getOpcode(), NewShift1, NewShift2);
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}
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Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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assert(Op0->getType() == Op1->getType());
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// If the shift amount is a one-use `sext`, we can demote it to `zext`.
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Value *Y;
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if (match(Op1, m_OneUse(m_SExt(m_Value(Y))))) {
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Value *NewExt = Builder.CreateZExt(Y, I.getType(), Op1->getName());
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return BinaryOperator::Create(I.getOpcode(), Op0, NewExt);
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}
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// See if we can fold away this shift.
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if (SimplifyDemandedInstructionBits(I))
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return &I;
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// Try to fold constant and into select arguments.
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if (isa<Constant>(Op0))
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if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
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if (Instruction *R = FoldOpIntoSelect(I, SI))
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return R;
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if (Constant *CUI = dyn_cast<Constant>(Op1))
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if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
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return Res;
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if (auto *NewShift = cast_or_null<Instruction>(
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reassociateShiftAmtsOfTwoSameDirectionShifts(&I, SQ)))
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return NewShift;
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// (C1 shift (A add C2)) -> (C1 shift C2) shift A)
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// iff A and C2 are both positive.
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Value *A;
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Constant *C;
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if (match(Op0, m_Constant()) && match(Op1, m_Add(m_Value(A), m_Constant(C))))
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if (isKnownNonNegative(A, DL, 0, &AC, &I, &DT) &&
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isKnownNonNegative(C, DL, 0, &AC, &I, &DT))
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return BinaryOperator::Create(
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I.getOpcode(), Builder.CreateBinOp(I.getOpcode(), Op0, C), A);
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// X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2.
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// Because shifts by negative values (which could occur if A were negative)
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// are undefined.
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const APInt *B;
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if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) {
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// FIXME: Should this get moved into SimplifyDemandedBits by saying we don't
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// demand the sign bit (and many others) here??
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Value *Rem = Builder.CreateAnd(A, ConstantInt::get(I.getType(), *B - 1),
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Op1->getName());
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I.setOperand(1, Rem);
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return &I;
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}
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if (Instruction *Logic = foldShiftOfShiftedLogic(I, Builder))
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return Logic;
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return nullptr;
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}
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/// Return true if we can simplify two logical (either left or right) shifts
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/// that have constant shift amounts: OuterShift (InnerShift X, C1), C2.
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static bool canEvaluateShiftedShift(unsigned OuterShAmt, bool IsOuterShl,
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Instruction *InnerShift, InstCombiner &IC,
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Instruction *CxtI) {
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assert(InnerShift->isLogicalShift() && "Unexpected instruction type");
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// We need constant scalar or constant splat shifts.
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const APInt *InnerShiftConst;
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if (!match(InnerShift->getOperand(1), m_APInt(InnerShiftConst)))
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return false;
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// Two logical shifts in the same direction:
|
|
// shl (shl X, C1), C2 --> shl X, C1 + C2
|
|
// lshr (lshr X, C1), C2 --> lshr X, C1 + C2
|
|
bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
|
|
if (IsInnerShl == IsOuterShl)
|
|
return true;
|
|
|
|
// Equal shift amounts in opposite directions become bitwise 'and':
|
|
// lshr (shl X, C), C --> and X, C'
|
|
// shl (lshr X, C), C --> and X, C'
|
|
if (*InnerShiftConst == OuterShAmt)
|
|
return true;
|
|
|
|
// If the 2nd shift is bigger than the 1st, we can fold:
|
|
// lshr (shl X, C1), C2 --> and (shl X, C1 - C2), C3
|
|
// shl (lshr X, C1), C2 --> and (lshr X, C1 - C2), C3
|
|
// but it isn't profitable unless we know the and'd out bits are already zero.
|
|
// Also, check that the inner shift is valid (less than the type width) or
|
|
// we'll crash trying to produce the bit mask for the 'and'.
|
|
unsigned TypeWidth = InnerShift->getType()->getScalarSizeInBits();
|
|
if (InnerShiftConst->ugt(OuterShAmt) && InnerShiftConst->ult(TypeWidth)) {
|
|
unsigned InnerShAmt = InnerShiftConst->getZExtValue();
|
|
unsigned MaskShift =
|
|
IsInnerShl ? TypeWidth - InnerShAmt : InnerShAmt - OuterShAmt;
|
|
APInt Mask = APInt::getLowBitsSet(TypeWidth, OuterShAmt) << MaskShift;
|
|
if (IC.MaskedValueIsZero(InnerShift->getOperand(0), Mask, 0, CxtI))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// See if we can compute the specified value, but shifted logically to the left
|
|
/// or right by some number of bits. This should return true if the expression
|
|
/// can be computed for the same cost as the current expression tree. This is
|
|
/// used to eliminate extraneous shifting from things like:
|
|
/// %C = shl i128 %A, 64
|
|
/// %D = shl i128 %B, 96
|
|
/// %E = or i128 %C, %D
|
|
/// %F = lshr i128 %E, 64
|
|
/// where the client will ask if E can be computed shifted right by 64-bits. If
|
|
/// this succeeds, getShiftedValue() will be called to produce the value.
|
|
static bool canEvaluateShifted(Value *V, unsigned NumBits, bool IsLeftShift,
|
|
InstCombiner &IC, Instruction *CxtI) {
|
|
// We can always evaluate constants shifted.
|
|
if (isa<Constant>(V))
|
|
return true;
|
|
|
|
Instruction *I = dyn_cast<Instruction>(V);
|
|
if (!I) return false;
|
|
|
|
// If this is the opposite shift, we can directly reuse the input of the shift
|
|
// if the needed bits are already zero in the input. This allows us to reuse
|
|
// the value which means that we don't care if the shift has multiple uses.
|
|
// TODO: Handle opposite shift by exact value.
|
|
ConstantInt *CI = nullptr;
|
|
if ((IsLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) ||
|
|
(!IsLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) {
|
|
if (CI->getValue() == NumBits) {
|
|
// TODO: Check that the input bits are already zero with MaskedValueIsZero
|
|
#if 0
|
|
// If this is a truncate of a logical shr, we can truncate it to a smaller
|
|
// lshr iff we know that the bits we would otherwise be shifting in are
|
|
// already zeros.
|
|
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
|
|
uint32_t BitWidth = Ty->getScalarSizeInBits();
|
|
if (MaskedValueIsZero(I->getOperand(0),
|
|
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
|
|
CI->getLimitedValue(BitWidth) < BitWidth) {
|
|
return CanEvaluateTruncated(I->getOperand(0), Ty);
|
|
}
|
|
#endif
|
|
|
|
}
|
|
}
|
|
|
|
// We can't mutate something that has multiple uses: doing so would
|
|
// require duplicating the instruction in general, which isn't profitable.
|
|
if (!I->hasOneUse()) return false;
|
|
|
|
switch (I->getOpcode()) {
|
|
default: return false;
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
// Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
|
|
return canEvaluateShifted(I->getOperand(0), NumBits, IsLeftShift, IC, I) &&
|
|
canEvaluateShifted(I->getOperand(1), NumBits, IsLeftShift, IC, I);
|
|
|
|
case Instruction::Shl:
|
|
case Instruction::LShr:
|
|
return canEvaluateShiftedShift(NumBits, IsLeftShift, I, IC, CxtI);
|
|
|
|
case Instruction::Select: {
|
|
SelectInst *SI = cast<SelectInst>(I);
|
|
Value *TrueVal = SI->getTrueValue();
|
|
Value *FalseVal = SI->getFalseValue();
|
|
return canEvaluateShifted(TrueVal, NumBits, IsLeftShift, IC, SI) &&
|
|
canEvaluateShifted(FalseVal, NumBits, IsLeftShift, IC, SI);
|
|
}
|
|
case Instruction::PHI: {
|
|
// We can change a phi if we can change all operands. Note that we never
|
|
// get into trouble with cyclic PHIs here because we only consider
|
|
// instructions with a single use.
|
|
PHINode *PN = cast<PHINode>(I);
|
|
for (Value *IncValue : PN->incoming_values())
|
|
if (!canEvaluateShifted(IncValue, NumBits, IsLeftShift, IC, PN))
|
|
return false;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Fold OuterShift (InnerShift X, C1), C2.
|
|
/// See canEvaluateShiftedShift() for the constraints on these instructions.
|
|
static Value *foldShiftedShift(BinaryOperator *InnerShift, unsigned OuterShAmt,
|
|
bool IsOuterShl,
|
|
InstCombiner::BuilderTy &Builder) {
|
|
bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
|
|
Type *ShType = InnerShift->getType();
|
|
unsigned TypeWidth = ShType->getScalarSizeInBits();
|
|
|
|
// We only accept shifts-by-a-constant in canEvaluateShifted().
|
|
const APInt *C1;
|
|
match(InnerShift->getOperand(1), m_APInt(C1));
|
|
unsigned InnerShAmt = C1->getZExtValue();
|
|
|
|
// Change the shift amount and clear the appropriate IR flags.
|
|
auto NewInnerShift = [&](unsigned ShAmt) {
|
|
InnerShift->setOperand(1, ConstantInt::get(ShType, ShAmt));
|
|
if (IsInnerShl) {
|
|
InnerShift->setHasNoUnsignedWrap(false);
|
|
InnerShift->setHasNoSignedWrap(false);
|
|
} else {
|
|
InnerShift->setIsExact(false);
|
|
}
|
|
return InnerShift;
|
|
};
|
|
|
|
// Two logical shifts in the same direction:
|
|
// shl (shl X, C1), C2 --> shl X, C1 + C2
|
|
// lshr (lshr X, C1), C2 --> lshr X, C1 + C2
|
|
if (IsInnerShl == IsOuterShl) {
|
|
// If this is an oversized composite shift, then unsigned shifts get 0.
|
|
if (InnerShAmt + OuterShAmt >= TypeWidth)
|
|
return Constant::getNullValue(ShType);
|
|
|
|
return NewInnerShift(InnerShAmt + OuterShAmt);
|
|
}
|
|
|
|
// Equal shift amounts in opposite directions become bitwise 'and':
|
|
// lshr (shl X, C), C --> and X, C'
|
|
// shl (lshr X, C), C --> and X, C'
|
|
if (InnerShAmt == OuterShAmt) {
|
|
APInt Mask = IsInnerShl
|
|
? APInt::getLowBitsSet(TypeWidth, TypeWidth - OuterShAmt)
|
|
: APInt::getHighBitsSet(TypeWidth, TypeWidth - OuterShAmt);
|
|
Value *And = Builder.CreateAnd(InnerShift->getOperand(0),
|
|
ConstantInt::get(ShType, Mask));
|
|
if (auto *AndI = dyn_cast<Instruction>(And)) {
|
|
AndI->moveBefore(InnerShift);
|
|
AndI->takeName(InnerShift);
|
|
}
|
|
return And;
|
|
}
|
|
|
|
assert(InnerShAmt > OuterShAmt &&
|
|
"Unexpected opposite direction logical shift pair");
|
|
|
|
// In general, we would need an 'and' for this transform, but
|
|
// canEvaluateShiftedShift() guarantees that the masked-off bits are not used.
|
|
// lshr (shl X, C1), C2 --> shl X, C1 - C2
|
|
// shl (lshr X, C1), C2 --> lshr X, C1 - C2
|
|
return NewInnerShift(InnerShAmt - OuterShAmt);
|
|
}
|
|
|
|
/// When canEvaluateShifted() returns true for an expression, this function
|
|
/// inserts the new computation that produces the shifted value.
|
|
static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
|
|
InstCombiner &IC, const DataLayout &DL) {
|
|
// We can always evaluate constants shifted.
|
|
if (Constant *C = dyn_cast<Constant>(V)) {
|
|
if (isLeftShift)
|
|
V = IC.Builder.CreateShl(C, NumBits);
|
|
else
|
|
V = IC.Builder.CreateLShr(C, NumBits);
|
|
// If we got a constantexpr back, try to simplify it with TD info.
|
|
if (auto *C = dyn_cast<Constant>(V))
|
|
if (auto *FoldedC =
|
|
ConstantFoldConstant(C, DL, &IC.getTargetLibraryInfo()))
|
|
V = FoldedC;
|
|
return V;
|
|
}
|
|
|
|
Instruction *I = cast<Instruction>(V);
|
|
IC.Worklist.Add(I);
|
|
|
|
switch (I->getOpcode()) {
|
|
default: llvm_unreachable("Inconsistency with CanEvaluateShifted");
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
// Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
|
|
I->setOperand(
|
|
0, getShiftedValue(I->getOperand(0), NumBits, isLeftShift, IC, DL));
|
|
I->setOperand(
|
|
1, getShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
|
|
return I;
|
|
|
|
case Instruction::Shl:
|
|
case Instruction::LShr:
|
|
return foldShiftedShift(cast<BinaryOperator>(I), NumBits, isLeftShift,
|
|
IC.Builder);
|
|
|
|
case Instruction::Select:
|
|
I->setOperand(
|
|
1, getShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
|
|
I->setOperand(
|
|
2, getShiftedValue(I->getOperand(2), NumBits, isLeftShift, IC, DL));
|
|
return I;
|
|
case Instruction::PHI: {
|
|
// We can change a phi if we can change all operands. Note that we never
|
|
// get into trouble with cyclic PHIs here because we only consider
|
|
// instructions with a single use.
|
|
PHINode *PN = cast<PHINode>(I);
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
PN->setIncomingValue(i, getShiftedValue(PN->getIncomingValue(i), NumBits,
|
|
isLeftShift, IC, DL));
|
|
return PN;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If this is a bitwise operator or add with a constant RHS we might be able
|
|
// to pull it through a shift.
|
|
static bool canShiftBinOpWithConstantRHS(BinaryOperator &Shift,
|
|
BinaryOperator *BO) {
|
|
switch (BO->getOpcode()) {
|
|
default:
|
|
return false; // Do not perform transform!
|
|
case Instruction::Add:
|
|
return Shift.getOpcode() == Instruction::Shl;
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
case Instruction::And:
|
|
return true;
|
|
}
|
|
}
|
|
|
|
Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
|
|
BinaryOperator &I) {
|
|
bool isLeftShift = I.getOpcode() == Instruction::Shl;
|
|
|
|
const APInt *Op1C;
|
|
if (!match(Op1, m_APInt(Op1C)))
|
|
return nullptr;
|
|
|
|
// See if we can propagate this shift into the input, this covers the trivial
|
|
// cast of lshr(shl(x,c1),c2) as well as other more complex cases.
|
|
if (I.getOpcode() != Instruction::AShr &&
|
|
canEvaluateShifted(Op0, Op1C->getZExtValue(), isLeftShift, *this, &I)) {
|
|
LLVM_DEBUG(
|
|
dbgs() << "ICE: GetShiftedValue propagating shift through expression"
|
|
" to eliminate shift:\n IN: "
|
|
<< *Op0 << "\n SH: " << I << "\n");
|
|
|
|
return replaceInstUsesWith(
|
|
I, getShiftedValue(Op0, Op1C->getZExtValue(), isLeftShift, *this, DL));
|
|
}
|
|
|
|
// See if we can simplify any instructions used by the instruction whose sole
|
|
// purpose is to compute bits we don't care about.
|
|
unsigned TypeBits = Op0->getType()->getScalarSizeInBits();
|
|
|
|
assert(!Op1C->uge(TypeBits) &&
|
|
"Shift over the type width should have been removed already");
|
|
|
|
if (Instruction *FoldedShift = foldBinOpIntoSelectOrPhi(I))
|
|
return FoldedShift;
|
|
|
|
// Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2))
|
|
if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) {
|
|
Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0));
|
|
// If 'shift2' is an ashr, we would have to get the sign bit into a funny
|
|
// place. Don't try to do this transformation in this case. Also, we
|
|
// require that the input operand is a shift-by-constant so that we have
|
|
// confidence that the shifts will get folded together. We could do this
|
|
// xform in more cases, but it is unlikely to be profitable.
|
|
if (TrOp && I.isLogicalShift() && TrOp->isShift() &&
|
|
isa<ConstantInt>(TrOp->getOperand(1))) {
|
|
// Okay, we'll do this xform. Make the shift of shift.
|
|
Constant *ShAmt =
|
|
ConstantExpr::getZExt(cast<Constant>(Op1), TrOp->getType());
|
|
// (shift2 (shift1 & 0x00FF), c2)
|
|
Value *NSh = Builder.CreateBinOp(I.getOpcode(), TrOp, ShAmt, I.getName());
|
|
|
|
// For logical shifts, the truncation has the effect of making the high
|
|
// part of the register be zeros. Emulate this by inserting an AND to
|
|
// clear the top bits as needed. This 'and' will usually be zapped by
|
|
// other xforms later if dead.
|
|
unsigned SrcSize = TrOp->getType()->getScalarSizeInBits();
|
|
unsigned DstSize = TI->getType()->getScalarSizeInBits();
|
|
APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize));
|
|
|
|
// The mask we constructed says what the trunc would do if occurring
|
|
// between the shifts. We want to know the effect *after* the second
|
|
// shift. We know that it is a logical shift by a constant, so adjust the
|
|
// mask as appropriate.
|
|
if (I.getOpcode() == Instruction::Shl)
|
|
MaskV <<= Op1C->getZExtValue();
|
|
else {
|
|
assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
|
|
MaskV.lshrInPlace(Op1C->getZExtValue());
|
|
}
|
|
|
|
// shift1 & 0x00FF
|
|
Value *And = Builder.CreateAnd(NSh,
|
|
ConstantInt::get(I.getContext(), MaskV),
|
|
TI->getName());
|
|
|
|
// Return the value truncated to the interesting size.
|
|
return new TruncInst(And, I.getType());
|
|
}
|
|
}
|
|
|
|
if (Op0->hasOneUse()) {
|
|
if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
|
|
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
|
|
Value *V1, *V2;
|
|
ConstantInt *CC;
|
|
switch (Op0BO->getOpcode()) {
|
|
default: break;
|
|
case Instruction::Add:
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor: {
|
|
// These operators commute.
|
|
// Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C)
|
|
if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() &&
|
|
match(Op0BO->getOperand(1), m_Shr(m_Value(V1),
|
|
m_Specific(Op1)))) {
|
|
Value *YS = // (Y << C)
|
|
Builder.CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
|
|
// (X + (Y << C))
|
|
Value *X = Builder.CreateBinOp(Op0BO->getOpcode(), YS, V1,
|
|
Op0BO->getOperand(1)->getName());
|
|
unsigned Op1Val = Op1C->getLimitedValue(TypeBits);
|
|
|
|
APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
|
|
Constant *Mask = ConstantInt::get(I.getContext(), Bits);
|
|
if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
|
|
Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
|
|
return BinaryOperator::CreateAnd(X, Mask);
|
|
}
|
|
|
|
// Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C))
|
|
Value *Op0BOOp1 = Op0BO->getOperand(1);
|
|
if (isLeftShift && Op0BOOp1->hasOneUse() &&
|
|
match(Op0BOOp1,
|
|
m_And(m_OneUse(m_Shr(m_Value(V1), m_Specific(Op1))),
|
|
m_ConstantInt(CC)))) {
|
|
Value *YS = // (Y << C)
|
|
Builder.CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
|
|
// X & (CC << C)
|
|
Value *XM = Builder.CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
|
|
V1->getName()+".mask");
|
|
return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
|
|
}
|
|
LLVM_FALLTHROUGH;
|
|
}
|
|
|
|
case Instruction::Sub: {
|
|
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
|
|
if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
|
|
match(Op0BO->getOperand(0), m_Shr(m_Value(V1),
|
|
m_Specific(Op1)))) {
|
|
Value *YS = // (Y << C)
|
|
Builder.CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
|
|
// (X + (Y << C))
|
|
Value *X = Builder.CreateBinOp(Op0BO->getOpcode(), V1, YS,
|
|
Op0BO->getOperand(0)->getName());
|
|
unsigned Op1Val = Op1C->getLimitedValue(TypeBits);
|
|
|
|
APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
|
|
Constant *Mask = ConstantInt::get(I.getContext(), Bits);
|
|
if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
|
|
Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
|
|
return BinaryOperator::CreateAnd(X, Mask);
|
|
}
|
|
|
|
// Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C)
|
|
if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
|
|
match(Op0BO->getOperand(0),
|
|
m_And(m_OneUse(m_Shr(m_Value(V1), m_Value(V2))),
|
|
m_ConstantInt(CC))) && V2 == Op1) {
|
|
Value *YS = // (Y << C)
|
|
Builder.CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
|
|
// X & (CC << C)
|
|
Value *XM = Builder.CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
|
|
V1->getName()+".mask");
|
|
|
|
return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS);
|
|
}
|
|
|
|
break;
|
|
}
|
|
}
|
|
|
|
|
|
// If the operand is a bitwise operator with a constant RHS, and the
|
|
// shift is the only use, we can pull it out of the shift.
|
|
const APInt *Op0C;
|
|
if (match(Op0BO->getOperand(1), m_APInt(Op0C))) {
|
|
if (canShiftBinOpWithConstantRHS(I, Op0BO)) {
|
|
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
|
|
cast<Constant>(Op0BO->getOperand(1)), Op1);
|
|
|
|
Value *NewShift =
|
|
Builder.CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
|
|
NewShift->takeName(Op0BO);
|
|
|
|
return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
|
|
NewRHS);
|
|
}
|
|
}
|
|
|
|
// If the operand is a subtract with a constant LHS, and the shift
|
|
// is the only use, we can pull it out of the shift.
|
|
// This folds (shl (sub C1, X), C2) -> (sub (C1 << C2), (shl X, C2))
|
|
if (isLeftShift && Op0BO->getOpcode() == Instruction::Sub &&
|
|
match(Op0BO->getOperand(0), m_APInt(Op0C))) {
|
|
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
|
|
cast<Constant>(Op0BO->getOperand(0)), Op1);
|
|
|
|
Value *NewShift = Builder.CreateShl(Op0BO->getOperand(1), Op1);
|
|
NewShift->takeName(Op0BO);
|
|
|
|
return BinaryOperator::CreateSub(NewRHS, NewShift);
|
|
}
|
|
}
|
|
|
|
// If we have a select that conditionally executes some binary operator,
|
|
// see if we can pull it the select and operator through the shift.
|
|
//
|
|
// For example, turning:
|
|
// shl (select C, (add X, C1), X), C2
|
|
// Into:
|
|
// Y = shl X, C2
|
|
// select C, (add Y, C1 << C2), Y
|
|
Value *Cond;
|
|
BinaryOperator *TBO;
|
|
Value *FalseVal;
|
|
if (match(Op0, m_Select(m_Value(Cond), m_OneUse(m_BinOp(TBO)),
|
|
m_Value(FalseVal)))) {
|
|
const APInt *C;
|
|
if (!isa<Constant>(FalseVal) && TBO->getOperand(0) == FalseVal &&
|
|
match(TBO->getOperand(1), m_APInt(C)) &&
|
|
canShiftBinOpWithConstantRHS(I, TBO)) {
|
|
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
|
|
cast<Constant>(TBO->getOperand(1)), Op1);
|
|
|
|
Value *NewShift =
|
|
Builder.CreateBinOp(I.getOpcode(), FalseVal, Op1);
|
|
Value *NewOp = Builder.CreateBinOp(TBO->getOpcode(), NewShift,
|
|
NewRHS);
|
|
return SelectInst::Create(Cond, NewOp, NewShift);
|
|
}
|
|
}
|
|
|
|
BinaryOperator *FBO;
|
|
Value *TrueVal;
|
|
if (match(Op0, m_Select(m_Value(Cond), m_Value(TrueVal),
|
|
m_OneUse(m_BinOp(FBO))))) {
|
|
const APInt *C;
|
|
if (!isa<Constant>(TrueVal) && FBO->getOperand(0) == TrueVal &&
|
|
match(FBO->getOperand(1), m_APInt(C)) &&
|
|
canShiftBinOpWithConstantRHS(I, FBO)) {
|
|
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
|
|
cast<Constant>(FBO->getOperand(1)), Op1);
|
|
|
|
Value *NewShift =
|
|
Builder.CreateBinOp(I.getOpcode(), TrueVal, Op1);
|
|
Value *NewOp = Builder.CreateBinOp(FBO->getOpcode(), NewShift,
|
|
NewRHS);
|
|
return SelectInst::Create(Cond, NewShift, NewOp);
|
|
}
|
|
}
|
|
}
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
Instruction *InstCombiner::visitShl(BinaryOperator &I) {
|
|
const SimplifyQuery Q = SQ.getWithInstruction(&I);
|
|
|
|
if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1),
|
|
I.hasNoSignedWrap(), I.hasNoUnsignedWrap(), Q))
|
|
return replaceInstUsesWith(I, V);
|
|
|
|
if (Instruction *X = foldVectorBinop(I))
|
|
return X;
|
|
|
|
if (Instruction *V = commonShiftTransforms(I))
|
|
return V;
|
|
|
|
if (Instruction *V = dropRedundantMaskingOfLeftShiftInput(&I, Q, Builder))
|
|
return V;
|
|
|
|
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
|
|
Type *Ty = I.getType();
|
|
unsigned BitWidth = Ty->getScalarSizeInBits();
|
|
|
|
const APInt *ShAmtAPInt;
|
|
if (match(Op1, m_APInt(ShAmtAPInt))) {
|
|
unsigned ShAmt = ShAmtAPInt->getZExtValue();
|
|
|
|
// shl (zext X), ShAmt --> zext (shl X, ShAmt)
|
|
// This is only valid if X would have zeros shifted out.
|
|
Value *X;
|
|
if (match(Op0, m_OneUse(m_ZExt(m_Value(X))))) {
|
|
unsigned SrcWidth = X->getType()->getScalarSizeInBits();
|
|
if (ShAmt < SrcWidth &&
|
|
MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmt), 0, &I))
|
|
return new ZExtInst(Builder.CreateShl(X, ShAmt), Ty);
|
|
}
|
|
|
|
// (X >> C) << C --> X & (-1 << C)
|
|
if (match(Op0, m_Shr(m_Value(X), m_Specific(Op1)))) {
|
|
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
|
|
return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
|
|
}
|
|
|
|
// FIXME: we do not yet transform non-exact shr's. The backend (DAGCombine)
|
|
// needs a few fixes for the rotate pattern recognition first.
|
|
const APInt *ShOp1;
|
|
if (match(Op0, m_Exact(m_Shr(m_Value(X), m_APInt(ShOp1))))) {
|
|
unsigned ShrAmt = ShOp1->getZExtValue();
|
|
if (ShrAmt < ShAmt) {
|
|
// If C1 < C2: (X >>?,exact C1) << C2 --> X << (C2 - C1)
|
|
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShrAmt);
|
|
auto *NewShl = BinaryOperator::CreateShl(X, ShiftDiff);
|
|
NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
|
|
NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
|
|
return NewShl;
|
|
}
|
|
if (ShrAmt > ShAmt) {
|
|
// If C1 > C2: (X >>?exact C1) << C2 --> X >>?exact (C1 - C2)
|
|
Constant *ShiftDiff = ConstantInt::get(Ty, ShrAmt - ShAmt);
|
|
auto *NewShr = BinaryOperator::Create(
|
|
cast<BinaryOperator>(Op0)->getOpcode(), X, ShiftDiff);
|
|
NewShr->setIsExact(true);
|
|
return NewShr;
|
|
}
|
|
}
|
|
|
|
if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1)))) {
|
|
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
|
|
// Oversized shifts are simplified to zero in InstSimplify.
|
|
if (AmtSum < BitWidth)
|
|
// (X << C1) << C2 --> X << (C1 + C2)
|
|
return BinaryOperator::CreateShl(X, ConstantInt::get(Ty, AmtSum));
|
|
}
|
|
|
|
// If the shifted-out value is known-zero, then this is a NUW shift.
|
|
if (!I.hasNoUnsignedWrap() &&
|
|
MaskedValueIsZero(Op0, APInt::getHighBitsSet(BitWidth, ShAmt), 0, &I)) {
|
|
I.setHasNoUnsignedWrap();
|
|
return &I;
|
|
}
|
|
|
|
// If the shifted-out value is all signbits, then this is a NSW shift.
|
|
if (!I.hasNoSignedWrap() && ComputeNumSignBits(Op0, 0, &I) > ShAmt) {
|
|
I.setHasNoSignedWrap();
|
|
return &I;
|
|
}
|
|
}
|
|
|
|
// Transform (x >> y) << y to x & (-1 << y)
|
|
// Valid for any type of right-shift.
|
|
Value *X;
|
|
if (match(Op0, m_OneUse(m_Shr(m_Value(X), m_Specific(Op1))))) {
|
|
Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
|
|
Value *Mask = Builder.CreateShl(AllOnes, Op1);
|
|
return BinaryOperator::CreateAnd(Mask, X);
|
|
}
|
|
|
|
Constant *C1;
|
|
if (match(Op1, m_Constant(C1))) {
|
|
Constant *C2;
|
|
Value *X;
|
|
// (C2 << X) << C1 --> (C2 << C1) << X
|
|
if (match(Op0, m_OneUse(m_Shl(m_Constant(C2), m_Value(X)))))
|
|
return BinaryOperator::CreateShl(ConstantExpr::getShl(C2, C1), X);
|
|
|
|
// (X * C2) << C1 --> X * (C2 << C1)
|
|
if (match(Op0, m_Mul(m_Value(X), m_Constant(C2))))
|
|
return BinaryOperator::CreateMul(X, ConstantExpr::getShl(C2, C1));
|
|
|
|
// shl (zext i1 X), C1 --> select (X, 1 << C1, 0)
|
|
if (match(Op0, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
|
|
auto *NewC = ConstantExpr::getShl(ConstantInt::get(Ty, 1), C1);
|
|
return SelectInst::Create(X, NewC, ConstantInt::getNullValue(Ty));
|
|
}
|
|
}
|
|
|
|
// (1 << (C - x)) -> ((1 << C) >> x) if C is bitwidth - 1
|
|
if (match(Op0, m_One()) &&
|
|
match(Op1, m_Sub(m_SpecificInt(BitWidth - 1), m_Value(X))))
|
|
return BinaryOperator::CreateLShr(
|
|
ConstantInt::get(Ty, APInt::getSignMask(BitWidth)), X);
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
|
|
if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),
|
|
SQ.getWithInstruction(&I)))
|
|
return replaceInstUsesWith(I, V);
|
|
|
|
if (Instruction *X = foldVectorBinop(I))
|
|
return X;
|
|
|
|
if (Instruction *R = commonShiftTransforms(I))
|
|
return R;
|
|
|
|
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
|
|
Type *Ty = I.getType();
|
|
const APInt *ShAmtAPInt;
|
|
if (match(Op1, m_APInt(ShAmtAPInt))) {
|
|
unsigned ShAmt = ShAmtAPInt->getZExtValue();
|
|
unsigned BitWidth = Ty->getScalarSizeInBits();
|
|
auto *II = dyn_cast<IntrinsicInst>(Op0);
|
|
if (II && isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt &&
|
|
(II->getIntrinsicID() == Intrinsic::ctlz ||
|
|
II->getIntrinsicID() == Intrinsic::cttz ||
|
|
II->getIntrinsicID() == Intrinsic::ctpop)) {
|
|
// ctlz.i32(x)>>5 --> zext(x == 0)
|
|
// cttz.i32(x)>>5 --> zext(x == 0)
|
|
// ctpop.i32(x)>>5 --> zext(x == -1)
|
|
bool IsPop = II->getIntrinsicID() == Intrinsic::ctpop;
|
|
Constant *RHS = ConstantInt::getSigned(Ty, IsPop ? -1 : 0);
|
|
Value *Cmp = Builder.CreateICmpEQ(II->getArgOperand(0), RHS);
|
|
return new ZExtInst(Cmp, Ty);
|
|
}
|
|
|
|
Value *X;
|
|
const APInt *ShOp1;
|
|
if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1))) && ShOp1->ult(BitWidth)) {
|
|
if (ShOp1->ult(ShAmt)) {
|
|
unsigned ShlAmt = ShOp1->getZExtValue();
|
|
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShlAmt);
|
|
if (cast<BinaryOperator>(Op0)->hasNoUnsignedWrap()) {
|
|
// (X <<nuw C1) >>u C2 --> X >>u (C2 - C1)
|
|
auto *NewLShr = BinaryOperator::CreateLShr(X, ShiftDiff);
|
|
NewLShr->setIsExact(I.isExact());
|
|
return NewLShr;
|
|
}
|
|
// (X << C1) >>u C2 --> (X >>u (C2 - C1)) & (-1 >> C2)
|
|
Value *NewLShr = Builder.CreateLShr(X, ShiftDiff, "", I.isExact());
|
|
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
|
|
return BinaryOperator::CreateAnd(NewLShr, ConstantInt::get(Ty, Mask));
|
|
}
|
|
if (ShOp1->ugt(ShAmt)) {
|
|
unsigned ShlAmt = ShOp1->getZExtValue();
|
|
Constant *ShiftDiff = ConstantInt::get(Ty, ShlAmt - ShAmt);
|
|
if (cast<BinaryOperator>(Op0)->hasNoUnsignedWrap()) {
|
|
// (X <<nuw C1) >>u C2 --> X <<nuw (C1 - C2)
|
|
auto *NewShl = BinaryOperator::CreateShl(X, ShiftDiff);
|
|
NewShl->setHasNoUnsignedWrap(true);
|
|
return NewShl;
|
|
}
|
|
// (X << C1) >>u C2 --> X << (C1 - C2) & (-1 >> C2)
|
|
Value *NewShl = Builder.CreateShl(X, ShiftDiff);
|
|
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
|
|
return BinaryOperator::CreateAnd(NewShl, ConstantInt::get(Ty, Mask));
|
|
}
|
|
assert(*ShOp1 == ShAmt);
|
|
// (X << C) >>u C --> X & (-1 >>u C)
|
|
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
|
|
return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
|
|
}
|
|
|
|
if (match(Op0, m_OneUse(m_ZExt(m_Value(X)))) &&
|
|
(!Ty->isIntegerTy() || shouldChangeType(Ty, X->getType()))) {
|
|
assert(ShAmt < X->getType()->getScalarSizeInBits() &&
|
|
"Big shift not simplified to zero?");
|
|
// lshr (zext iM X to iN), C --> zext (lshr X, C) to iN
|
|
Value *NewLShr = Builder.CreateLShr(X, ShAmt);
|
|
return new ZExtInst(NewLShr, Ty);
|
|
}
|
|
|
|
if (match(Op0, m_SExt(m_Value(X))) &&
|
|
(!Ty->isIntegerTy() || shouldChangeType(Ty, X->getType()))) {
|
|
// Are we moving the sign bit to the low bit and widening with high zeros?
|
|
unsigned SrcTyBitWidth = X->getType()->getScalarSizeInBits();
|
|
if (ShAmt == BitWidth - 1) {
|
|
// lshr (sext i1 X to iN), N-1 --> zext X to iN
|
|
if (SrcTyBitWidth == 1)
|
|
return new ZExtInst(X, Ty);
|
|
|
|
// lshr (sext iM X to iN), N-1 --> zext (lshr X, M-1) to iN
|
|
if (Op0->hasOneUse()) {
|
|
Value *NewLShr = Builder.CreateLShr(X, SrcTyBitWidth - 1);
|
|
return new ZExtInst(NewLShr, Ty);
|
|
}
|
|
}
|
|
|
|
// lshr (sext iM X to iN), N-M --> zext (ashr X, min(N-M, M-1)) to iN
|
|
if (ShAmt == BitWidth - SrcTyBitWidth && Op0->hasOneUse()) {
|
|
// The new shift amount can't be more than the narrow source type.
|
|
unsigned NewShAmt = std::min(ShAmt, SrcTyBitWidth - 1);
|
|
Value *AShr = Builder.CreateAShr(X, NewShAmt);
|
|
return new ZExtInst(AShr, Ty);
|
|
}
|
|
}
|
|
|
|
if (match(Op0, m_LShr(m_Value(X), m_APInt(ShOp1)))) {
|
|
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
|
|
// Oversized shifts are simplified to zero in InstSimplify.
|
|
if (AmtSum < BitWidth)
|
|
// (X >>u C1) >>u C2 --> X >>u (C1 + C2)
|
|
return BinaryOperator::CreateLShr(X, ConstantInt::get(Ty, AmtSum));
|
|
}
|
|
|
|
// If the shifted-out value is known-zero, then this is an exact shift.
|
|
if (!I.isExact() &&
|
|
MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmt), 0, &I)) {
|
|
I.setIsExact();
|
|
return &I;
|
|
}
|
|
}
|
|
|
|
// Transform (x << y) >> y to x & (-1 >> y)
|
|
Value *X;
|
|
if (match(Op0, m_OneUse(m_Shl(m_Value(X), m_Specific(Op1))))) {
|
|
Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
|
|
Value *Mask = Builder.CreateLShr(AllOnes, Op1);
|
|
return BinaryOperator::CreateAnd(Mask, X);
|
|
}
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
Instruction *
|
|
InstCombiner::foldVariableSignZeroExtensionOfVariableHighBitExtract(
|
|
BinaryOperator &OldAShr) {
|
|
assert(OldAShr.getOpcode() == Instruction::AShr &&
|
|
"Must be called with arithmetic right-shift instruction only.");
|
|
|
|
// Check that constant C is a splat of the element-wise bitwidth of V.
|
|
auto BitWidthSplat = [](Constant *C, Value *V) {
|
|
return match(
|
|
C, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_EQ,
|
|
APInt(C->getType()->getScalarSizeInBits(),
|
|
V->getType()->getScalarSizeInBits())));
|
|
};
|
|
|
|
// It should look like variable-length sign-extension on the outside:
|
|
// (Val << (bitwidth(Val)-Nbits)) a>> (bitwidth(Val)-Nbits)
|
|
Value *NBits;
|
|
Instruction *MaybeTrunc;
|
|
Constant *C1, *C2;
|
|
if (!match(&OldAShr,
|
|
m_AShr(m_Shl(m_Instruction(MaybeTrunc),
|
|
m_ZExtOrSelf(m_Sub(m_Constant(C1),
|
|
m_ZExtOrSelf(m_Value(NBits))))),
|
|
m_ZExtOrSelf(m_Sub(m_Constant(C2),
|
|
m_ZExtOrSelf(m_Deferred(NBits)))))) ||
|
|
!BitWidthSplat(C1, &OldAShr) || !BitWidthSplat(C2, &OldAShr))
|
|
return nullptr;
|
|
|
|
// There may or may not be a truncation after outer two shifts.
|
|
Instruction *HighBitExtract;
|
|
match(MaybeTrunc, m_TruncOrSelf(m_Instruction(HighBitExtract)));
|
|
bool HadTrunc = MaybeTrunc != HighBitExtract;
|
|
|
|
// And finally, the innermost part of the pattern must be a right-shift.
|
|
Value *X, *NumLowBitsToSkip;
|
|
if (!match(HighBitExtract, m_Shr(m_Value(X), m_Value(NumLowBitsToSkip))))
|
|
return nullptr;
|
|
|
|
// Said right-shift must extract high NBits bits - C0 must be it's bitwidth.
|
|
Constant *C0;
|
|
if (!match(NumLowBitsToSkip,
|
|
m_ZExtOrSelf(
|
|
m_Sub(m_Constant(C0), m_ZExtOrSelf(m_Specific(NBits))))) ||
|
|
!BitWidthSplat(C0, HighBitExtract))
|
|
return nullptr;
|
|
|
|
// Since the NBits is identical for all shifts, if the outermost and
|
|
// innermost shifts are identical, then outermost shifts are redundant.
|
|
// If we had truncation, do keep it though.
|
|
if (HighBitExtract->getOpcode() == OldAShr.getOpcode())
|
|
return replaceInstUsesWith(OldAShr, MaybeTrunc);
|
|
|
|
// Else, if there was a truncation, then we need to ensure that one
|
|
// instruction will go away.
|
|
if (HadTrunc && !match(&OldAShr, m_c_BinOp(m_OneUse(m_Value()), m_Value())))
|
|
return nullptr;
|
|
|
|
// Finally, bypass two innermost shifts, and perform the outermost shift on
|
|
// the operands of the innermost shift.
|
|
Instruction *NewAShr =
|
|
BinaryOperator::Create(OldAShr.getOpcode(), X, NumLowBitsToSkip);
|
|
NewAShr->copyIRFlags(HighBitExtract); // We can preserve 'exact'-ness.
|
|
if (!HadTrunc)
|
|
return NewAShr;
|
|
|
|
Builder.Insert(NewAShr);
|
|
return TruncInst::CreateTruncOrBitCast(NewAShr, OldAShr.getType());
|
|
}
|
|
|
|
Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
|
|
if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),
|
|
SQ.getWithInstruction(&I)))
|
|
return replaceInstUsesWith(I, V);
|
|
|
|
if (Instruction *X = foldVectorBinop(I))
|
|
return X;
|
|
|
|
if (Instruction *R = commonShiftTransforms(I))
|
|
return R;
|
|
|
|
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
|
|
Type *Ty = I.getType();
|
|
unsigned BitWidth = Ty->getScalarSizeInBits();
|
|
const APInt *ShAmtAPInt;
|
|
if (match(Op1, m_APInt(ShAmtAPInt)) && ShAmtAPInt->ult(BitWidth)) {
|
|
unsigned ShAmt = ShAmtAPInt->getZExtValue();
|
|
|
|
// If the shift amount equals the difference in width of the destination
|
|
// and source scalar types:
|
|
// ashr (shl (zext X), C), C --> sext X
|
|
Value *X;
|
|
if (match(Op0, m_Shl(m_ZExt(m_Value(X)), m_Specific(Op1))) &&
|
|
ShAmt == BitWidth - X->getType()->getScalarSizeInBits())
|
|
return new SExtInst(X, Ty);
|
|
|
|
// We can't handle (X << C1) >>s C2. It shifts arbitrary bits in. However,
|
|
// we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
|
|
const APInt *ShOp1;
|
|
if (match(Op0, m_NSWShl(m_Value(X), m_APInt(ShOp1))) &&
|
|
ShOp1->ult(BitWidth)) {
|
|
unsigned ShlAmt = ShOp1->getZExtValue();
|
|
if (ShlAmt < ShAmt) {
|
|
// (X <<nsw C1) >>s C2 --> X >>s (C2 - C1)
|
|
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShlAmt);
|
|
auto *NewAShr = BinaryOperator::CreateAShr(X, ShiftDiff);
|
|
NewAShr->setIsExact(I.isExact());
|
|
return NewAShr;
|
|
}
|
|
if (ShlAmt > ShAmt) {
|
|
// (X <<nsw C1) >>s C2 --> X <<nsw (C1 - C2)
|
|
Constant *ShiftDiff = ConstantInt::get(Ty, ShlAmt - ShAmt);
|
|
auto *NewShl = BinaryOperator::Create(Instruction::Shl, X, ShiftDiff);
|
|
NewShl->setHasNoSignedWrap(true);
|
|
return NewShl;
|
|
}
|
|
}
|
|
|
|
if (match(Op0, m_AShr(m_Value(X), m_APInt(ShOp1))) &&
|
|
ShOp1->ult(BitWidth)) {
|
|
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
|
|
// Oversized arithmetic shifts replicate the sign bit.
|
|
AmtSum = std::min(AmtSum, BitWidth - 1);
|
|
// (X >>s C1) >>s C2 --> X >>s (C1 + C2)
|
|
return BinaryOperator::CreateAShr(X, ConstantInt::get(Ty, AmtSum));
|
|
}
|
|
|
|
if (match(Op0, m_OneUse(m_SExt(m_Value(X)))) &&
|
|
(Ty->isVectorTy() || shouldChangeType(Ty, X->getType()))) {
|
|
// ashr (sext X), C --> sext (ashr X, C')
|
|
Type *SrcTy = X->getType();
|
|
ShAmt = std::min(ShAmt, SrcTy->getScalarSizeInBits() - 1);
|
|
Value *NewSh = Builder.CreateAShr(X, ConstantInt::get(SrcTy, ShAmt));
|
|
return new SExtInst(NewSh, Ty);
|
|
}
|
|
|
|
// If the shifted-out value is known-zero, then this is an exact shift.
|
|
if (!I.isExact() &&
|
|
MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmt), 0, &I)) {
|
|
I.setIsExact();
|
|
return &I;
|
|
}
|
|
}
|
|
|
|
if (Instruction *R = foldVariableSignZeroExtensionOfVariableHighBitExtract(I))
|
|
return R;
|
|
|
|
// See if we can turn a signed shr into an unsigned shr.
|
|
if (MaskedValueIsZero(Op0, APInt::getSignMask(BitWidth), 0, &I))
|
|
return BinaryOperator::CreateLShr(Op0, Op1);
|
|
|
|
return nullptr;
|
|
}
|