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//===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===//
//
// 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 moves ARGUMENT instructions after ScheduleDAG scheduling.
///
/// Arguments are really live-in registers, however, since we use virtual
/// registers and LLVM doesn't support live-in virtual registers, we're
/// currently making do with ARGUMENT instructions which are placed at the top
/// of the entry block. The trick is to get them to *stay* at the top of the
/// entry block.
///
/// The ARGUMENTS physical register keeps these instructions pinned in place
/// during liveness-aware CodeGen passes, however one thing which does not
/// respect this is the ScheduleDAG scheduler. This pass is therefore run
/// immediately after that.
///
/// This is all hopefully a temporary solution until we find a better solution
/// for describing the live-in nature of arguments.
///
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "Utils/WebAssemblyUtilities.h"
#include "WebAssembly.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblySubtarget.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "wasm-argument-move"
namespace {
class WebAssemblyArgumentMove final : public MachineFunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
WebAssemblyArgumentMove() : MachineFunctionPass(ID) {}
StringRef getPassName() const override { return "WebAssembly Argument Move"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addPreserved<MachineBlockFrequencyInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
bool runOnMachineFunction(MachineFunction &MF) override;
};
} // end anonymous namespace
char WebAssemblyArgumentMove::ID = 0;
INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE,
"Move ARGUMENT instructions for WebAssembly", false, false)
FunctionPass *llvm::createWebAssemblyArgumentMove() {
return new WebAssemblyArgumentMove();
}
bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) {
LLVM_DEBUG({
dbgs() << "********** Argument Move **********\n"
<< "********** Function: " << MF.getName() << '\n';
});
bool Changed = false;
MachineBasicBlock &EntryMBB = MF.front();
MachineBasicBlock::iterator InsertPt = EntryMBB.end();
// Look for the first NonArg instruction.
for (MachineInstr &MI : EntryMBB) {
if (!WebAssembly::isArgument(MI.getOpcode())) {
InsertPt = MI;
break;
}
}
// Now move any argument instructions later in the block
// to before our first NonArg instruction.
for (MachineInstr &MI : llvm::make_range(InsertPt, EntryMBB.end())) {
if (WebAssembly::isArgument(MI.getOpcode())) {
EntryMBB.insert(InsertPt, MI.removeFromParent());
Changed = true;
}
}
return Changed;
}
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