llvm/llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp

//===-- FixupStatepointCallerSaved.cpp - Fixup caller saved registers  ----===//
//
// 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
/// Statepoint instruction in deopt parameters contains values which are
/// meaningful to the runtime and should be able to be read at the moment the
/// call returns. So we can say that we need to encode the fact that these
/// values are "late read" by runtime. If we could express this notion for
/// register allocator it would produce the right form for us.
/// The need to fixup (i.e this pass) is specifically handling the fact that
/// we cannot describe such a late read for the register allocator.
/// Register allocator may put the value on a register clobbered by the call.
/// This pass forces the spill of such registers and replaces corresponding
/// statepoint operands to added spill slots.
///
//===----------------------------------------------------------------------===//

#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/StackMaps.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/IR/Statepoint.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"

usingnamespacellvm;

#define DEBUG_TYPE …
STATISTIC(NumSpilledRegisters, "Number of spilled register");
STATISTIC(NumSpillSlotsAllocated, "Number of spill slots allocated");
STATISTIC(NumSpillSlotsExtended, "Number of spill slots extended");

static cl::opt<bool> FixupSCSExtendSlotSize(
    "fixup-scs-extend-slot-size", cl::Hidden, cl::init(false),
    cl::desc("Allow spill in spill slot of greater size than register size"),
    cl::Hidden);

static cl::opt<bool> PassGCPtrInCSR(
    "fixup-allow-gcptr-in-csr", cl::Hidden, cl::init(false),
    cl::desc("Allow passing GC Pointer arguments in callee saved registers"));

static cl::opt<bool> EnableCopyProp(
    "fixup-scs-enable-copy-propagation", cl::Hidden, cl::init(true),
    cl::desc("Enable simple copy propagation during register reloading"));

// This is purely debugging option.
// It may be handy for investigating statepoint spilling issues.
static cl::opt<unsigned> MaxStatepointsWithRegs(
    "fixup-max-csr-statepoints", cl::Hidden,
    cl::desc("Max number of statepoints allowed to pass GC Ptrs in registers"));

namespace {

class FixupStatepointCallerSaved : public MachineFunctionPass { … };

} // End anonymous namespace.

char FixupStatepointCallerSaved::ID = …;
char &llvm::FixupStatepointCallerSavedID = …;

INITIALIZE_PASS_BEGIN(FixupStatepointCallerSaved, DEBUG_TYPE,
                      "Fixup Statepoint Caller Saved", false, false)
INITIALIZE_PASS_END(FixupStatepointCallerSaved, DEBUG_TYPE,
                    "Fixup Statepoint Caller Saved", false, false)

// Utility function to get size of the register.
static unsigned getRegisterSize(const TargetRegisterInfo &TRI, Register Reg) { … }

// Try to eliminate redundant copy to register which we're going to
// spill, i.e. try to change:
//    X = COPY Y
//    SPILL X
//  to
//    SPILL Y
//  If there are no uses of X between copy and STATEPOINT, that COPY
//  may be eliminated.
//  Reg - register we're about to spill
//  RI - On entry points to statepoint.
//       On successful copy propagation set to new spill point.
//  IsKill - set to true if COPY is Kill (there are no uses of Y)
//  Returns either found source copy register or original one.
static Register performCopyPropagation(Register Reg,
                                       MachineBasicBlock::iterator &RI,
                                       bool &IsKill, const TargetInstrInfo &TII,
                                       const TargetRegisterInfo &TRI) { … }

namespace {
// Pair {Register, FrameIndex}
RegSlotPair;

// Keeps track of what reloads were inserted in MBB.
class RegReloadCache { … };

// Cache used frame indexes during statepoint re-write to re-use them in
// processing next statepoint instruction.
// Two strategies. One is to preserve the size of spill slot while another one
// extends the size of spill slots to reduce the number of them, causing
// the less total frame size. But unspill will have "implicit" any extend.
class FrameIndexesCache { … };

// Describes the state of the current processing statepoint instruction.
class StatepointState { … };

class StatepointProcessor { … };
} // namespace

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