llvm/llvm/lib/Target/WebAssembly/WebAssemblyMemIntrinsicResults.cpp

//== WebAssemblyMemIntrinsicResults.cpp - Optimize memory intrinsic results ==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file implements an optimization pass using memory intrinsic results.
///
/// Calls to memory intrinsics (memcpy, memmove, memset) return the destination
/// address. They are in the form of
///   %dst_new = call @memcpy %dst, %src, %len
/// where %dst and %dst_new registers contain the same value.
///
/// This is to enable an optimization wherein uses of the %dst register used in
/// the parameter can be replaced by uses of the %dst_new register used in the
/// result, making the %dst register more likely to be single-use, thus more
/// likely to be useful to register stackifying, and potentially also exposing
/// the call instruction itself to register stackifying. These both can reduce
/// local.get/local.set traffic.
///
/// The LLVM intrinsics for these return void so they can't use the returned
/// attribute and consequently aren't handled by the OptimizeReturned pass.
///
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssembly.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblySubtarget.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
usingnamespacellvm;

#define DEBUG_TYPE …

namespace {
class WebAssemblyMemIntrinsicResults final : public MachineFunctionPass { … };
} // end anonymous namespace

char WebAssemblyMemIntrinsicResults::ID = …;
INITIALIZE_PASS(…)

FunctionPass *llvm::createWebAssemblyMemIntrinsicResults() { … }

// Replace uses of FromReg with ToReg if they are dominated by MI.
static bool replaceDominatedUses(MachineBasicBlock &MBB, MachineInstr &MI,
                                 unsigned FromReg, unsigned ToReg,
                                 const MachineRegisterInfo &MRI,
                                 MachineDominatorTree &MDT,
                                 LiveIntervals &LIS) { … }

static bool optimizeCall(MachineBasicBlock &MBB, MachineInstr &MI,
                         const MachineRegisterInfo &MRI,
                         MachineDominatorTree &MDT, LiveIntervals &LIS,
                         const WebAssemblyTargetLowering &TLI,
                         const TargetLibraryInfo &LibInfo) { … }

bool WebAssemblyMemIntrinsicResults::runOnMachineFunction(MachineFunction &MF) { … }