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629 lines
24 KiB
629 lines
24 KiB
//===- ConstantHoisting.cpp - Prepare code for expensive constants --------===//
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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 pass identifies expensive constants to hoist and coalesces them to
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// better prepare it for SelectionDAG-based code generation. This works around
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// the limitations of the basic-block-at-a-time approach.
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//
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// First it scans all instructions for integer constants and calculates its
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// cost. If the constant can be folded into the instruction (the cost is
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// TCC_Free) or the cost is just a simple operation (TCC_BASIC), then we don't
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// consider it expensive and leave it alone. This is the default behavior and
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// the default implementation of getIntImmCost will always return TCC_Free.
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//
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// If the cost is more than TCC_BASIC, then the integer constant can't be folded
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// into the instruction and it might be beneficial to hoist the constant.
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// Similar constants are coalesced to reduce register pressure and
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// materialization code.
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//
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// When a constant is hoisted, it is also hidden behind a bitcast to force it to
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// be live-out of the basic block. Otherwise the constant would be just
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// duplicated and each basic block would have its own copy in the SelectionDAG.
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// The SelectionDAG recognizes such constants as opaque and doesn't perform
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// certain transformations on them, which would create a new expensive constant.
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//
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// This optimization is only applied to integer constants in instructions and
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// simple (this means not nested) constant cast expressions. For example:
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// %0 = load i64* inttoptr (i64 big_constant to i64*)
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/ConstantHoisting.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Scalar.h"
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#include <tuple>
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using namespace llvm;
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using namespace consthoist;
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#define DEBUG_TYPE "consthoist"
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STATISTIC(NumConstantsHoisted, "Number of constants hoisted");
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STATISTIC(NumConstantsRebased, "Number of constants rebased");
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namespace {
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/// \brief The constant hoisting pass.
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class ConstantHoistingLegacyPass : public FunctionPass {
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public:
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static char ID; // Pass identification, replacement for typeid
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ConstantHoistingLegacyPass() : FunctionPass(ID) {
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initializeConstantHoistingLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &Fn) override;
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const char *getPassName() const override { return "Constant Hoisting"; }
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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}
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void releaseMemory() override { Impl.releaseMemory(); }
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private:
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ConstantHoistingPass Impl;
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};
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}
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char ConstantHoistingLegacyPass::ID = 0;
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INITIALIZE_PASS_BEGIN(ConstantHoistingLegacyPass, "consthoist",
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"Constant Hoisting", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_END(ConstantHoistingLegacyPass, "consthoist",
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"Constant Hoisting", false, false)
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FunctionPass *llvm::createConstantHoistingPass() {
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return new ConstantHoistingLegacyPass();
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}
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/// \brief Perform the constant hoisting optimization for the given function.
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bool ConstantHoistingLegacyPass::runOnFunction(Function &Fn) {
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if (skipFunction(Fn))
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return false;
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DEBUG(dbgs() << "********** Begin Constant Hoisting **********\n");
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DEBUG(dbgs() << "********** Function: " << Fn.getName() << '\n');
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bool MadeChange = Impl.runImpl(
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Fn, getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn),
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getAnalysis<DominatorTreeWrapperPass>().getDomTree(), Fn.getEntryBlock());
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if (MadeChange) {
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DEBUG(dbgs() << "********** Function after Constant Hoisting: "
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<< Fn.getName() << '\n');
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DEBUG(dbgs() << Fn);
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}
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DEBUG(dbgs() << "********** End Constant Hoisting **********\n");
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return MadeChange;
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}
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/// \brief Find the constant materialization insertion point.
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Instruction *ConstantHoistingPass::findMatInsertPt(Instruction *Inst,
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unsigned Idx) const {
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// If the operand is a cast instruction, then we have to materialize the
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// constant before the cast instruction.
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if (Idx != ~0U) {
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Value *Opnd = Inst->getOperand(Idx);
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if (auto CastInst = dyn_cast<Instruction>(Opnd))
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if (CastInst->isCast())
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return CastInst;
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}
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// The simple and common case. This also includes constant expressions.
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if (!isa<PHINode>(Inst) && !Inst->isEHPad())
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return Inst;
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// We can't insert directly before a phi node or an eh pad. Insert before
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// the terminator of the incoming or dominating block.
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assert(Entry != Inst->getParent() && "PHI or landing pad in entry block!");
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if (Idx != ~0U && isa<PHINode>(Inst))
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return cast<PHINode>(Inst)->getIncomingBlock(Idx)->getTerminator();
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BasicBlock *IDom = DT->getNode(Inst->getParent())->getIDom()->getBlock();
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return IDom->getTerminator();
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}
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/// \brief Find an insertion point that dominates all uses.
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Instruction *ConstantHoistingPass::findConstantInsertionPoint(
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const ConstantInfo &ConstInfo) const {
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assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
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// Collect all basic blocks.
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SmallPtrSet<BasicBlock *, 8> BBs;
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for (auto const &RCI : ConstInfo.RebasedConstants)
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for (auto const &U : RCI.Uses)
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BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());
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if (BBs.count(Entry))
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return &Entry->front();
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while (BBs.size() >= 2) {
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BasicBlock *BB, *BB1, *BB2;
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BB1 = *BBs.begin();
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BB2 = *std::next(BBs.begin());
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BB = DT->findNearestCommonDominator(BB1, BB2);
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if (BB == Entry)
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return &Entry->front();
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BBs.erase(BB1);
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BBs.erase(BB2);
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BBs.insert(BB);
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}
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assert((BBs.size() == 1) && "Expected only one element.");
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Instruction &FirstInst = (*BBs.begin())->front();
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return findMatInsertPt(&FirstInst);
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}
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/// \brief Record constant integer ConstInt for instruction Inst at operand
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/// index Idx.
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///
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/// The operand at index Idx is not necessarily the constant integer itself. It
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/// could also be a cast instruction or a constant expression that uses the
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// constant integer.
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void ConstantHoistingPass::collectConstantCandidates(
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ConstCandMapType &ConstCandMap, Instruction *Inst, unsigned Idx,
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ConstantInt *ConstInt) {
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unsigned Cost;
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// Ask the target about the cost of materializing the constant for the given
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// instruction and operand index.
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if (auto IntrInst = dyn_cast<IntrinsicInst>(Inst))
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Cost = TTI->getIntImmCost(IntrInst->getIntrinsicID(), Idx,
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ConstInt->getValue(), ConstInt->getType());
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else
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Cost = TTI->getIntImmCost(Inst->getOpcode(), Idx, ConstInt->getValue(),
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ConstInt->getType());
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// Ignore cheap integer constants.
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if (Cost > TargetTransformInfo::TCC_Basic) {
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ConstCandMapType::iterator Itr;
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bool Inserted;
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std::tie(Itr, Inserted) = ConstCandMap.insert(std::make_pair(ConstInt, 0));
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if (Inserted) {
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ConstCandVec.push_back(ConstantCandidate(ConstInt));
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Itr->second = ConstCandVec.size() - 1;
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}
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ConstCandVec[Itr->second].addUser(Inst, Idx, Cost);
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DEBUG(if (isa<ConstantInt>(Inst->getOperand(Idx)))
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dbgs() << "Collect constant " << *ConstInt << " from " << *Inst
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<< " with cost " << Cost << '\n';
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else
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dbgs() << "Collect constant " << *ConstInt << " indirectly from "
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<< *Inst << " via " << *Inst->getOperand(Idx) << " with cost "
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<< Cost << '\n';
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);
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}
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}
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/// \brief Scan the instruction for expensive integer constants and record them
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/// in the constant candidate vector.
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void ConstantHoistingPass::collectConstantCandidates(
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ConstCandMapType &ConstCandMap, Instruction *Inst) {
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// Skip all cast instructions. They are visited indirectly later on.
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if (Inst->isCast())
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return;
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// Can't handle inline asm. Skip it.
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if (auto Call = dyn_cast<CallInst>(Inst))
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if (isa<InlineAsm>(Call->getCalledValue()))
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return;
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// Switch cases must remain constant, and if the value being tested is
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// constant the entire thing should disappear.
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if (isa<SwitchInst>(Inst))
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return;
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// Static allocas (constant size in the entry block) are handled by
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// prologue/epilogue insertion so they're free anyway. We definitely don't
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// want to make them non-constant.
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auto AI = dyn_cast<AllocaInst>(Inst);
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if (AI && AI->isStaticAlloca())
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return;
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// Scan all operands.
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for (unsigned Idx = 0, E = Inst->getNumOperands(); Idx != E; ++Idx) {
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Value *Opnd = Inst->getOperand(Idx);
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// Visit constant integers.
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if (auto ConstInt = dyn_cast<ConstantInt>(Opnd)) {
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collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
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continue;
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}
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// Visit cast instructions that have constant integers.
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if (auto CastInst = dyn_cast<Instruction>(Opnd)) {
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// Only visit cast instructions, which have been skipped. All other
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// instructions should have already been visited.
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if (!CastInst->isCast())
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continue;
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if (auto *ConstInt = dyn_cast<ConstantInt>(CastInst->getOperand(0))) {
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// Pretend the constant is directly used by the instruction and ignore
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// the cast instruction.
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collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
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continue;
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}
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}
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// Visit constant expressions that have constant integers.
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if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) {
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// Only visit constant cast expressions.
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if (!ConstExpr->isCast())
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continue;
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if (auto ConstInt = dyn_cast<ConstantInt>(ConstExpr->getOperand(0))) {
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// Pretend the constant is directly used by the instruction and ignore
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// the constant expression.
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collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
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continue;
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}
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}
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} // end of for all operands
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}
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/// \brief Collect all integer constants in the function that cannot be folded
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/// into an instruction itself.
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void ConstantHoistingPass::collectConstantCandidates(Function &Fn) {
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ConstCandMapType ConstCandMap;
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for (BasicBlock &BB : Fn)
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for (Instruction &Inst : BB)
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collectConstantCandidates(ConstCandMap, &Inst);
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}
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// This helper function is necessary to deal with values that have different
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// bit widths (APInt Operator- does not like that). If the value cannot be
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// represented in uint64 we return an "empty" APInt. This is then interpreted
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// as the value is not in range.
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static llvm::Optional<APInt> calculateOffsetDiff(APInt V1, APInt V2)
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{
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llvm::Optional<APInt> Res = None;
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unsigned BW = V1.getBitWidth() > V2.getBitWidth() ?
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V1.getBitWidth() : V2.getBitWidth();
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uint64_t LimVal1 = V1.getLimitedValue();
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uint64_t LimVal2 = V2.getLimitedValue();
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if (LimVal1 == ~0ULL || LimVal2 == ~0ULL)
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return Res;
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uint64_t Diff = LimVal1 - LimVal2;
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return APInt(BW, Diff, true);
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}
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// From a list of constants, one needs to picked as the base and the other
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// constants will be transformed into an offset from that base constant. The
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// question is which we can pick best? For example, consider these constants
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// and their number of uses:
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//
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// Constants| 2 | 4 | 12 | 42 |
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// NumUses | 3 | 2 | 8 | 7 |
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//
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// Selecting constant 12 because it has the most uses will generate negative
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// offsets for constants 2 and 4 (i.e. -10 and -8 respectively). If negative
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// offsets lead to less optimal code generation, then there might be better
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// solutions. Suppose immediates in the range of 0..35 are most optimally
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// supported by the architecture, then selecting constant 2 is most optimal
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// because this will generate offsets: 0, 2, 10, 40. Offsets 0, 2 and 10 are in
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// range 0..35, and thus 3 + 2 + 8 = 13 uses are in range. Selecting 12 would
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// have only 8 uses in range, so choosing 2 as a base is more optimal. Thus, in
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// selecting the base constant the range of the offsets is a very important
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// factor too that we take into account here. This algorithm calculates a total
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// costs for selecting a constant as the base and substract the costs if
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// immediates are out of range. It has quadratic complexity, so we call this
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// function only when we're optimising for size and there are less than 100
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// constants, we fall back to the straightforward algorithm otherwise
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// which does not do all the offset calculations.
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unsigned
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ConstantHoistingPass::maximizeConstantsInRange(ConstCandVecType::iterator S,
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ConstCandVecType::iterator E,
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ConstCandVecType::iterator &MaxCostItr) {
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unsigned NumUses = 0;
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if(!Entry->getParent()->optForSize() || std::distance(S,E) > 100) {
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for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
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NumUses += ConstCand->Uses.size();
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if (ConstCand->CumulativeCost > MaxCostItr->CumulativeCost)
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MaxCostItr = ConstCand;
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}
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return NumUses;
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}
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DEBUG(dbgs() << "== Maximize constants in range ==\n");
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int MaxCost = -1;
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for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
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auto Value = ConstCand->ConstInt->getValue();
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Type *Ty = ConstCand->ConstInt->getType();
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int Cost = 0;
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NumUses += ConstCand->Uses.size();
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DEBUG(dbgs() << "= Constant: " << ConstCand->ConstInt->getValue() << "\n");
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for (auto User : ConstCand->Uses) {
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unsigned Opcode = User.Inst->getOpcode();
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unsigned OpndIdx = User.OpndIdx;
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Cost += TTI->getIntImmCost(Opcode, OpndIdx, Value, Ty);
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DEBUG(dbgs() << "Cost: " << Cost << "\n");
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for (auto C2 = S; C2 != E; ++C2) {
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llvm::Optional<APInt> Diff = calculateOffsetDiff(
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C2->ConstInt->getValue(),
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ConstCand->ConstInt->getValue());
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if (Diff) {
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const int ImmCosts =
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TTI->getIntImmCodeSizeCost(Opcode, OpndIdx, Diff.getValue(), Ty);
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Cost -= ImmCosts;
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DEBUG(dbgs() << "Offset " << Diff.getValue() << " "
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<< "has penalty: " << ImmCosts << "\n"
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<< "Adjusted cost: " << Cost << "\n");
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}
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}
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}
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DEBUG(dbgs() << "Cumulative cost: " << Cost << "\n");
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if (Cost > MaxCost) {
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MaxCost = Cost;
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MaxCostItr = ConstCand;
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DEBUG(dbgs() << "New candidate: " << MaxCostItr->ConstInt->getValue()
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<< "\n");
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}
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}
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return NumUses;
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}
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/// \brief Find the base constant within the given range and rebase all other
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/// constants with respect to the base constant.
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void ConstantHoistingPass::findAndMakeBaseConstant(
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ConstCandVecType::iterator S, ConstCandVecType::iterator E) {
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auto MaxCostItr = S;
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unsigned NumUses = maximizeConstantsInRange(S, E, MaxCostItr);
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// Don't hoist constants that have only one use.
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if (NumUses <= 1)
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return;
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ConstantInfo ConstInfo;
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ConstInfo.BaseConstant = MaxCostItr->ConstInt;
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Type *Ty = ConstInfo.BaseConstant->getType();
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// Rebase the constants with respect to the base constant.
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for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
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APInt Diff = ConstCand->ConstInt->getValue() -
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ConstInfo.BaseConstant->getValue();
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Constant *Offset = Diff == 0 ? nullptr : ConstantInt::get(Ty, Diff);
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ConstInfo.RebasedConstants.push_back(
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RebasedConstantInfo(std::move(ConstCand->Uses), Offset));
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}
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ConstantVec.push_back(std::move(ConstInfo));
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}
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/// \brief Finds and combines constant candidates that can be easily
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/// rematerialized with an add from a common base constant.
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void ConstantHoistingPass::findBaseConstants() {
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// Sort the constants by value and type. This invalidates the mapping!
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std::sort(ConstCandVec.begin(), ConstCandVec.end(),
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[](const ConstantCandidate &LHS, const ConstantCandidate &RHS) {
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if (LHS.ConstInt->getType() != RHS.ConstInt->getType())
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return LHS.ConstInt->getType()->getBitWidth() <
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RHS.ConstInt->getType()->getBitWidth();
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return LHS.ConstInt->getValue().ult(RHS.ConstInt->getValue());
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});
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// Simple linear scan through the sorted constant candidate vector for viable
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// merge candidates.
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auto MinValItr = ConstCandVec.begin();
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for (auto CC = std::next(ConstCandVec.begin()), E = ConstCandVec.end();
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CC != E; ++CC) {
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if (MinValItr->ConstInt->getType() == CC->ConstInt->getType()) {
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// Check if the constant is in range of an add with immediate.
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APInt Diff = CC->ConstInt->getValue() - MinValItr->ConstInt->getValue();
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if ((Diff.getBitWidth() <= 64) &&
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TTI->isLegalAddImmediate(Diff.getSExtValue()))
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continue;
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}
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// We either have now a different constant type or the constant is not in
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// range of an add with immediate anymore.
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findAndMakeBaseConstant(MinValItr, CC);
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// Start a new base constant search.
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MinValItr = CC;
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}
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// Finalize the last base constant search.
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findAndMakeBaseConstant(MinValItr, ConstCandVec.end());
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}
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/// \brief Updates the operand at Idx in instruction Inst with the result of
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/// instruction Mat. If the instruction is a PHI node then special
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/// handling for duplicate values form the same incomming basic block is
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/// required.
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/// \return The update will always succeed, but the return value indicated if
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/// Mat was used for the update or not.
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static bool updateOperand(Instruction *Inst, unsigned Idx, Instruction *Mat) {
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if (auto PHI = dyn_cast<PHINode>(Inst)) {
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// Check if any previous operand of the PHI node has the same incoming basic
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// block. This is a very odd case that happens when the incoming basic block
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// has a switch statement. In this case use the same value as the previous
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// operand(s), otherwise we will fail verification due to different values.
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// The values are actually the same, but the variable names are different
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// and the verifier doesn't like that.
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BasicBlock *IncomingBB = PHI->getIncomingBlock(Idx);
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for (unsigned i = 0; i < Idx; ++i) {
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if (PHI->getIncomingBlock(i) == IncomingBB) {
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Value *IncomingVal = PHI->getIncomingValue(i);
|
|
Inst->setOperand(Idx, IncomingVal);
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
|
|
Inst->setOperand(Idx, Mat);
|
|
return true;
|
|
}
|
|
|
|
/// \brief Emit materialization code for all rebased constants and update their
|
|
/// users.
|
|
void ConstantHoistingPass::emitBaseConstants(Instruction *Base,
|
|
Constant *Offset,
|
|
const ConstantUser &ConstUser) {
|
|
Instruction *Mat = Base;
|
|
if (Offset) {
|
|
Instruction *InsertionPt = findMatInsertPt(ConstUser.Inst,
|
|
ConstUser.OpndIdx);
|
|
Mat = BinaryOperator::Create(Instruction::Add, Base, Offset,
|
|
"const_mat", InsertionPt);
|
|
|
|
DEBUG(dbgs() << "Materialize constant (" << *Base->getOperand(0)
|
|
<< " + " << *Offset << ") in BB "
|
|
<< Mat->getParent()->getName() << '\n' << *Mat << '\n');
|
|
Mat->setDebugLoc(ConstUser.Inst->getDebugLoc());
|
|
}
|
|
Value *Opnd = ConstUser.Inst->getOperand(ConstUser.OpndIdx);
|
|
|
|
// Visit constant integer.
|
|
if (isa<ConstantInt>(Opnd)) {
|
|
DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n');
|
|
if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, Mat) && Offset)
|
|
Mat->eraseFromParent();
|
|
DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n');
|
|
return;
|
|
}
|
|
|
|
// Visit cast instruction.
|
|
if (auto CastInst = dyn_cast<Instruction>(Opnd)) {
|
|
assert(CastInst->isCast() && "Expected an cast instruction!");
|
|
// Check if we already have visited this cast instruction before to avoid
|
|
// unnecessary cloning.
|
|
Instruction *&ClonedCastInst = ClonedCastMap[CastInst];
|
|
if (!ClonedCastInst) {
|
|
ClonedCastInst = CastInst->clone();
|
|
ClonedCastInst->setOperand(0, Mat);
|
|
ClonedCastInst->insertAfter(CastInst);
|
|
// Use the same debug location as the original cast instruction.
|
|
ClonedCastInst->setDebugLoc(CastInst->getDebugLoc());
|
|
DEBUG(dbgs() << "Clone instruction: " << *CastInst << '\n'
|
|
<< "To : " << *ClonedCastInst << '\n');
|
|
}
|
|
|
|
DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n');
|
|
updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ClonedCastInst);
|
|
DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n');
|
|
return;
|
|
}
|
|
|
|
// Visit constant expression.
|
|
if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) {
|
|
Instruction *ConstExprInst = ConstExpr->getAsInstruction();
|
|
ConstExprInst->setOperand(0, Mat);
|
|
ConstExprInst->insertBefore(findMatInsertPt(ConstUser.Inst,
|
|
ConstUser.OpndIdx));
|
|
|
|
// Use the same debug location as the instruction we are about to update.
|
|
ConstExprInst->setDebugLoc(ConstUser.Inst->getDebugLoc());
|
|
|
|
DEBUG(dbgs() << "Create instruction: " << *ConstExprInst << '\n'
|
|
<< "From : " << *ConstExpr << '\n');
|
|
DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n');
|
|
if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ConstExprInst)) {
|
|
ConstExprInst->eraseFromParent();
|
|
if (Offset)
|
|
Mat->eraseFromParent();
|
|
}
|
|
DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n');
|
|
return;
|
|
}
|
|
}
|
|
|
|
/// \brief Hoist and hide the base constant behind a bitcast and emit
|
|
/// materialization code for derived constants.
|
|
bool ConstantHoistingPass::emitBaseConstants() {
|
|
bool MadeChange = false;
|
|
for (auto const &ConstInfo : ConstantVec) {
|
|
// Hoist and hide the base constant behind a bitcast.
|
|
Instruction *IP = findConstantInsertionPoint(ConstInfo);
|
|
IntegerType *Ty = ConstInfo.BaseConstant->getType();
|
|
Instruction *Base =
|
|
new BitCastInst(ConstInfo.BaseConstant, Ty, "const", IP);
|
|
DEBUG(dbgs() << "Hoist constant (" << *ConstInfo.BaseConstant << ") to BB "
|
|
<< IP->getParent()->getName() << '\n' << *Base << '\n');
|
|
NumConstantsHoisted++;
|
|
|
|
// Emit materialization code for all rebased constants.
|
|
for (auto const &RCI : ConstInfo.RebasedConstants) {
|
|
NumConstantsRebased++;
|
|
for (auto const &U : RCI.Uses)
|
|
emitBaseConstants(Base, RCI.Offset, U);
|
|
}
|
|
|
|
// Use the same debug location as the last user of the constant.
|
|
assert(!Base->use_empty() && "The use list is empty!?");
|
|
assert(isa<Instruction>(Base->user_back()) &&
|
|
"All uses should be instructions.");
|
|
Base->setDebugLoc(cast<Instruction>(Base->user_back())->getDebugLoc());
|
|
|
|
// Correct for base constant, which we counted above too.
|
|
NumConstantsRebased--;
|
|
MadeChange = true;
|
|
}
|
|
return MadeChange;
|
|
}
|
|
|
|
/// \brief Check all cast instructions we made a copy of and remove them if they
|
|
/// have no more users.
|
|
void ConstantHoistingPass::deleteDeadCastInst() const {
|
|
for (auto const &I : ClonedCastMap)
|
|
if (I.first->use_empty())
|
|
I.first->eraseFromParent();
|
|
}
|
|
|
|
/// \brief Optimize expensive integer constants in the given function.
|
|
bool ConstantHoistingPass::runImpl(Function &Fn, TargetTransformInfo &TTI,
|
|
DominatorTree &DT, BasicBlock &Entry) {
|
|
this->TTI = &TTI;
|
|
this->DT = &DT;
|
|
this->Entry = &Entry;
|
|
// Collect all constant candidates.
|
|
collectConstantCandidates(Fn);
|
|
|
|
// There are no constant candidates to worry about.
|
|
if (ConstCandVec.empty())
|
|
return false;
|
|
|
|
// Combine constants that can be easily materialized with an add from a common
|
|
// base constant.
|
|
findBaseConstants();
|
|
|
|
// There are no constants to emit.
|
|
if (ConstantVec.empty())
|
|
return false;
|
|
|
|
// Finally hoist the base constant and emit materialization code for dependent
|
|
// constants.
|
|
bool MadeChange = emitBaseConstants();
|
|
|
|
// Cleanup dead instructions.
|
|
deleteDeadCastInst();
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
PreservedAnalyses ConstantHoistingPass::run(Function &F,
|
|
FunctionAnalysisManager &AM) {
|
|
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
|
|
auto &TTI = AM.getResult<TargetIRAnalysis>(F);
|
|
if (!runImpl(F, TTI, DT, F.getEntryBlock()))
|
|
return PreservedAnalyses::all();
|
|
|
|
// FIXME: This should also 'preserve the CFG'.
|
|
return PreservedAnalyses::none();
|
|
}
|