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//===- HexagonGenExtract.cpp ----------------------------------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include <algorithm>
#include <cstdint>
#include <iterator>
using namespace llvm;
static cl::opt<unsigned> ExtractCutoff("extract-cutoff", cl::init(~0U),
cl::Hidden, cl::desc("Cutoff for generating \"extract\""
" instructions"));
// This prevents generating extract instructions that have the offset of 0.
// One of the reasons for "extract" is to put a sequence of bits in a regis-
// ter, starting at offset 0 (so that these bits can then be used by an
// "insert"). If the bits are already at offset 0, it is better not to gene-
// rate "extract", since logical bit operations can be merged into compound
// instructions (as opposed to "extract").
static cl::opt<bool> NoSR0("extract-nosr0", cl::init(true), cl::Hidden,
cl::desc("No extract instruction with offset 0"));
static cl::opt<bool> NeedAnd("extract-needand", cl::init(true), cl::Hidden,
cl::desc("Require & in extract patterns"));
namespace llvm {
void initializeHexagonGenExtractPass(PassRegistry&);
FunctionPass *createHexagonGenExtract();
} // end namespace llvm
namespace {
class HexagonGenExtract : public FunctionPass {
static char ID;
HexagonGenExtract() : FunctionPass(ID) {
StringRef getPassName() const override {
return "Hexagon generate \"extract\" instructions";
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool visitBlock(BasicBlock *B);
bool convert(Instruction *In);
unsigned ExtractCount = 0;
DominatorTree *DT;
} // end anonymous namespace
char HexagonGenExtract::ID = 0;
INITIALIZE_PASS_BEGIN(HexagonGenExtract, "hextract", "Hexagon generate "
"\"extract\" instructions", false, false)
INITIALIZE_PASS_END(HexagonGenExtract, "hextract", "Hexagon generate "
"\"extract\" instructions", false, false)
bool HexagonGenExtract::convert(Instruction *In) {
using namespace PatternMatch;
Value *BF = nullptr;
ConstantInt *CSL = nullptr, *CSR = nullptr, *CM = nullptr;
BasicBlock *BB = In->getParent();
LLVMContext &Ctx = BB->getContext();
bool LogicalSR;
// (and (shl (lshr x, #sr), #sl), #m)
LogicalSR = true;
bool Match = match(In, m_And(m_Shl(m_LShr(m_Value(BF), m_ConstantInt(CSR)),
if (!Match) {
// (and (shl (ashr x, #sr), #sl), #m)
LogicalSR = false;
Match = match(In, m_And(m_Shl(m_AShr(m_Value(BF), m_ConstantInt(CSR)),
if (!Match) {
// (and (shl x, #sl), #m)
LogicalSR = true;
CSR = ConstantInt::get(Type::getInt32Ty(Ctx), 0);
Match = match(In, m_And(m_Shl(m_Value(BF), m_ConstantInt(CSL)),
if (Match && NoSR0)
return false;
if (!Match) {
// (and (lshr x, #sr), #m)
LogicalSR = true;
CSL = ConstantInt::get(Type::getInt32Ty(Ctx), 0);
Match = match(In, m_And(m_LShr(m_Value(BF), m_ConstantInt(CSR)),
if (!Match) {
// (and (ashr x, #sr), #m)
LogicalSR = false;
CSL = ConstantInt::get(Type::getInt32Ty(Ctx), 0);
Match = match(In, m_And(m_AShr(m_Value(BF), m_ConstantInt(CSR)),
if (!Match) {
CM = nullptr;
// (shl (lshr x, #sr), #sl)
LogicalSR = true;
Match = match(In, m_Shl(m_LShr(m_Value(BF), m_ConstantInt(CSR)),
if (!Match) {
CM = nullptr;
// (shl (ashr x, #sr), #sl)
LogicalSR = false;
Match = match(In, m_Shl(m_AShr(m_Value(BF), m_ConstantInt(CSR)),
if (!Match)
return false;
Type *Ty = BF->getType();
if (!Ty->isIntegerTy())
return false;
unsigned BW = Ty->getPrimitiveSizeInBits();
if (BW != 32 && BW != 64)
return false;
uint32_t SR = CSR->getZExtValue();
uint32_t SL = CSL->getZExtValue();
if (!CM) {
// If there was no and, and the shift left did not remove all potential
// sign bits created by the shift right, then extractu cannot reproduce
// this value.
if (!LogicalSR && (SR > SL))
return false;
APInt A = APInt(BW, ~0ULL).lshr(SR).shl(SL);
CM = ConstantInt::get(Ctx, A);
// CM is the shifted-left mask. Shift it back right to remove the zero
// bits on least-significant positions.
APInt M = CM->getValue().lshr(SL);
uint32_t T = M.countTrailingOnes();
// During the shifts some of the bits will be lost. Calculate how many
// of the original value will remain after shift right and then left.
uint32_t U = BW - std::max(SL, SR);
// The width of the extracted field is the minimum of the original bits
// that remain after the shifts and the number of contiguous 1s in the mask.
uint32_t W = std::min(U, T);
if (W == 0)
return false;
// Check if the extracted bits are contained within the mask that it is
// and-ed with. The extract operation will copy these bits, and so the
// mask cannot any holes in it that would clear any of the bits of the
// extracted field.
if (!LogicalSR) {
// If the shift right was arithmetic, it could have included some 1 bits.
// It is still ok to generate extract, but only if the mask eliminates
// those bits (i.e. M does not have any bits set beyond U).
APInt C = APInt::getHighBitsSet(BW, BW-U);
if (M.intersects(C) || !M.isMask(W))
return false;
} else {
// Check if M starts with a contiguous sequence of W times 1 bits. Get
// the low U bits of M (which eliminates the 0 bits shifted in on the
// left), and check if the result is APInt's "mask":
if (!M.getLoBits(U).isMask(W))
return false;
IRBuilder<> IRB(In);
Intrinsic::ID IntId = (BW == 32) ? Intrinsic::hexagon_S2_extractu
: Intrinsic::hexagon_S2_extractup;
Module *Mod = BB->getParent()->getParent();
Value *ExtF = Intrinsic::getDeclaration(Mod, IntId);
Value *NewIn = IRB.CreateCall(ExtF, {BF, IRB.getInt32(W), IRB.getInt32(SR)});
if (SL != 0)
NewIn = IRB.CreateShl(NewIn, SL, CSL->getName());
return true;
bool HexagonGenExtract::visitBlock(BasicBlock *B) {
// Depth-first, bottom-up traversal.
for (auto *DTN : children<DomTreeNode*>(DT->getNode(B)))
// Allow limiting the number of generated extracts for debugging purposes.
bool HasCutoff = ExtractCutoff.getPosition();
unsigned Cutoff = ExtractCutoff;
bool Changed = false;
BasicBlock::iterator I = std::prev(B->end()), NextI, Begin = B->begin();
while (true) {
if (HasCutoff && (ExtractCount >= Cutoff))
return Changed;
bool Last = (I == Begin);
if (!Last)
NextI = std::prev(I);
Instruction *In = &*I;
bool Done = convert(In);
if (HasCutoff && Done)
Changed |= Done;
if (Last)
I = NextI;
return Changed;
bool HexagonGenExtract::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
bool Changed;
// Traverse the function bottom-up, to see super-expressions before their
// sub-expressions.
BasicBlock *Entry = GraphTraits<Function*>::getEntryNode(&F);
Changed = visitBlock(Entry);
return Changed;
FunctionPass *llvm::createHexagonGenExtract() {
return new HexagonGenExtract();