forked from OSchip/llvm-project
102 lines
3.2 KiB
C++
102 lines
3.2 KiB
C++
//===-- ARMOptimizeBarriersPass - two DMBs without a memory access in between,
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//removed one -===//
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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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#include "ARM.h"
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#include "ARMInstrInfo.h"
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#include "ARMMachineFunctionInfo.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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using namespace llvm;
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#define DEBUG_TYPE "double barriers"
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STATISTIC(NumDMBsRemoved, "Number of DMBs removed");
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namespace {
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class ARMOptimizeBarriersPass : public MachineFunctionPass {
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public:
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static char ID;
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ARMOptimizeBarriersPass() : MachineFunctionPass(ID) {}
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bool runOnMachineFunction(MachineFunction &Fn) override;
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const char *getPassName() const override {
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return "optimise barriers pass";
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}
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private:
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};
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char ARMOptimizeBarriersPass::ID = 0;
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}
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// Returns whether the instruction can safely move past a DMB instruction
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// The current implementation allows this iif MI does not have any possible
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// memory access
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static bool CanMovePastDMB(const MachineInstr *MI) {
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return !(MI->mayLoad() ||
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MI->mayStore() ||
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MI->hasUnmodeledSideEffects() ||
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MI->isCall() ||
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MI->isReturn());
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}
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bool ARMOptimizeBarriersPass::runOnMachineFunction(MachineFunction &MF) {
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// Vector to store the DMBs we will remove after the first iteration
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std::vector<MachineInstr *> ToRemove;
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// DMBType is the Imm value of the first operand. It determines whether it's a
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// DMB ish, dmb sy, dmb osh, etc
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int64_t DMBType = -1;
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// Find a dmb. If we can move it until the next dmb, tag the second one for
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// removal
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for (auto &MBB : MF) {
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// Will be true when we have seen a DMB, and not seen any instruction since
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// that cannot move past a DMB
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bool IsRemovableNextDMB = false;
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for (auto &MI : MBB) {
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if (MI.getOpcode() == ARM::DMB) {
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if (IsRemovableNextDMB) {
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// If the Imm of this DMB is the same as that of the last DMB, we can
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// tag this second DMB for removal
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if (MI.getOperand(0).getImm() == DMBType) {
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ToRemove.push_back(&MI);
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} else {
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// If it has a different DMBType, we cannot remove it, but will scan
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// for the next DMB, recording this DMB's type as last seen DMB type
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DMBType = MI.getOperand(0).getImm();
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}
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} else {
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// After we see a DMB, a next one is removable
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IsRemovableNextDMB = true;
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DMBType = MI.getOperand(0).getImm();
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}
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} else if (!CanMovePastDMB(&MI)) {
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// If we find an instruction unable to pass past a DMB, a next DMB is
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// not removable
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IsRemovableNextDMB = false;
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}
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}
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}
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// Remove the tagged DMB
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for (auto MI : ToRemove) {
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MI->eraseFromParent();
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++NumDMBsRemoved;
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}
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return NumDMBsRemoved > 0;
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}
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/// createARMOptimizeBarriersPass - Returns an instance of the remove double
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/// barriers
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/// pass.
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FunctionPass *llvm::createARMOptimizeBarriersPass() {
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return new ARMOptimizeBarriersPass();
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}
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