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//===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief 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 "WebAssembly.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssemblyMachineFunctionInfo.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) {}
const char *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;
FunctionPass *llvm::createWebAssemblyArgumentMove() {
return new WebAssemblyArgumentMove();
}
/// Test whether the given instruction is an ARGUMENT.
static bool IsArgument(const MachineInstr *MI) {
switch (MI->getOpcode()) {
case WebAssembly::ARGUMENT_I32:
case WebAssembly::ARGUMENT_I64:
case WebAssembly::ARGUMENT_F32:
case WebAssembly::ARGUMENT_F64:
return true;
default:
return false;
}
}
bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) {
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 (auto MII = EntryMBB.begin(), MIE = EntryMBB.end(); MII != MIE; ++MII) {
MachineInstr *MI = MII;
if (!IsArgument(MI)) {
InsertPt = MII;
break;
}
}
// Now move any argument instructions later in the block
// to before our first NonArg instruction.
for (auto I = InsertPt, E = EntryMBB.end(); I != E; ++I) {
MachineInstr *MI = I;
if (IsArgument(MI)) {
EntryMBB.insert(InsertPt, MI->removeFromParent());
Changed = true;
}
}
return Changed;
}
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