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author | Stephen Hines <srhines@google.com> | 2014-04-23 16:57:46 -0700 |
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committer | Stephen Hines <srhines@google.com> | 2014-04-24 15:53:16 -0700 |
commit | 36b56886974eae4f9c5ebc96befd3e7bfe5de338 (patch) | |
tree | e6cfb69fbbd937f450eeb83bfb83b9da3b01275a /lib/Target/ARM/ARMOptimizeBarriersPass.cpp | |
parent | 69a8640022b04415ae9fac62f8ab090601d8f889 (diff) | |
download | external_llvm-36b56886974eae4f9c5ebc96befd3e7bfe5de338.zip external_llvm-36b56886974eae4f9c5ebc96befd3e7bfe5de338.tar.gz external_llvm-36b56886974eae4f9c5ebc96befd3e7bfe5de338.tar.bz2 |
Update to LLVM 3.5a.
Change-Id: Ifadecab779f128e62e430c2b4f6ddd84953ed617
Diffstat (limited to 'lib/Target/ARM/ARMOptimizeBarriersPass.cpp')
-rw-r--r-- | lib/Target/ARM/ARMOptimizeBarriersPass.cpp | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/lib/Target/ARM/ARMOptimizeBarriersPass.cpp b/lib/Target/ARM/ARMOptimizeBarriersPass.cpp new file mode 100644 index 0000000..20619fa --- /dev/null +++ b/lib/Target/ARM/ARMOptimizeBarriersPass.cpp @@ -0,0 +1,101 @@ +//===-- ARMOptimizeBarriersPass - two DMBs without a memory access in between, +//removed one -===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===------------------------------------------------------------------------------------------===// + +#define DEBUG_TYPE "double barriers" + +#include "ARM.h" +#include "ARMMachineFunctionInfo.h" +#include "ARMInstrInfo.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +using namespace llvm; + +STATISTIC(NumDMBsRemoved, "Number of DMBs removed"); + +namespace { +class ARMOptimizeBarriersPass : public MachineFunctionPass { +public: + static char ID; + ARMOptimizeBarriersPass() : MachineFunctionPass(ID) {} + + virtual bool runOnMachineFunction(MachineFunction &Fn); + + virtual const char *getPassName() const { + return "optimise barriers pass"; + } + +private: +}; +char ARMOptimizeBarriersPass::ID = 0; +} + +// Returns whether the instruction can safely move past a DMB instruction +// The current implementation allows this iif MI does not have any possible +// memory access +static bool CanMovePastDMB(const MachineInstr *MI) { + return !(MI->mayLoad() || + MI->mayStore() || + MI->hasUnmodeledSideEffects() || + MI->isCall() || + MI->isReturn()); +} + +bool ARMOptimizeBarriersPass::runOnMachineFunction(MachineFunction &MF) { + // Vector to store the DMBs we will remove after the first iteration + std::vector<MachineInstr *> ToRemove; + // DMBType is the Imm value of the first operand. It determines whether it's a + // DMB ish, dmb sy, dmb osh, etc + int64_t DMBType = -1; + + // Find a dmb. If we can move it until the next dmb, tag the second one for + // removal + for (auto &MBB : MF) { + // Will be true when we have seen a DMB, and not seen any instruction since + // that cannot move past a DMB + bool IsRemovableNextDMB = false; + for (auto &MI : MBB) { + if (MI.getOpcode() == ARM::DMB) { + if (IsRemovableNextDMB) { + // If the Imm of this DMB is the same as that of the last DMB, we can + // tag this second DMB for removal + if (MI.getOperand(0).getImm() == DMBType) { + ToRemove.push_back(&MI); + } else { + // If it has a different DMBType, we cannot remove it, but will scan + // for the next DMB, recording this DMB's type as last seen DMB type + DMBType = MI.getOperand(0).getImm(); + } + } else { + // After we see a DMB, a next one is removable + IsRemovableNextDMB = true; + DMBType = MI.getOperand(0).getImm(); + } + } else if (!CanMovePastDMB(&MI)) { + // If we find an instruction unable to pass past a DMB, a next DMB is + // not removable + IsRemovableNextDMB = false; + } + } + } + // Remove the tagged DMB + for (auto MI : ToRemove) { + MI->eraseFromParent(); + ++NumDMBsRemoved; + } + + return NumDMBsRemoved > 0; +} + +/// createARMOptimizeBarriersPass - Returns an instance of the remove double +/// barriers +/// pass. +FunctionPass *llvm::createARMOptimizeBarriersPass() { + return new ARMOptimizeBarriersPass(); +} |