llvm/llvm/lib/CodeGen/RegAllocEvictionAdvisor.cpp

//===- RegAllocEvictionAdvisor.cpp - eviction advisor ---------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Implementation of the default eviction advisor and of the Analysis pass.
//
//===----------------------------------------------------------------------===//

#include "RegAllocEvictionAdvisor.h"
#include "AllocationOrder.h"
#include "RegAllocGreedy.h"
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Target/TargetMachine.h"

usingnamespacellvm;

static cl::opt<RegAllocEvictionAdvisorAnalysis::AdvisorMode> Mode(
    "regalloc-enable-advisor", cl::Hidden,
    cl::init(RegAllocEvictionAdvisorAnalysis::AdvisorMode::Default),
    cl::desc("Enable regalloc advisor mode"),
    cl::values(
        clEnumValN(RegAllocEvictionAdvisorAnalysis::AdvisorMode::Default,
                   "default", "Default"),
        clEnumValN(RegAllocEvictionAdvisorAnalysis::AdvisorMode::Release,
                   "release", "precompiled"),
        clEnumValN(RegAllocEvictionAdvisorAnalysis::AdvisorMode::Development,
                   "development", "for training")));

static cl::opt<bool> EnableLocalReassignment(
    "enable-local-reassign", cl::Hidden,
    cl::desc("Local reassignment can yield better allocation decisions, but "
             "may be compile time intensive"),
    cl::init(false));

namespace llvm {
cl::opt<unsigned> EvictInterferenceCutoff(
    "regalloc-eviction-max-interference-cutoff", cl::Hidden,
    cl::desc("Number of interferences after which we declare "
             "an interference unevictable and bail out. This "
             "is a compilation cost-saving consideration. To "
             "disable, pass a very large number."),
    cl::init(10));
}

#define DEBUG_TYPE …
#ifdef LLVM_HAVE_TF_AOT_REGALLOCEVICTMODEL
#define LLVM_HAVE_TF_AOT
#endif

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

namespace {
class DefaultEvictionAdvisorAnalysis final
    : public RegAllocEvictionAdvisorAnalysis { … };
} // namespace

template <> Pass *llvm::callDefaultCtor<RegAllocEvictionAdvisorAnalysis>() { … }

StringRef RegAllocEvictionAdvisorAnalysis::getPassName() const { … }

RegAllocEvictionAdvisor::RegAllocEvictionAdvisor(const MachineFunction &MF,
                                                 const RAGreedy &RA)
    : … { … }

/// shouldEvict - determine if A should evict the assigned live range B. The
/// eviction policy defined by this function together with the allocation order
/// defined by enqueue() decides which registers ultimately end up being split
/// and spilled.
///
/// Cascade numbers are used to prevent infinite loops if this function is a
/// cyclic relation.
///
/// @param A          The live range to be assigned.
/// @param IsHint     True when A is about to be assigned to its preferred
///                   register.
/// @param B          The live range to be evicted.
/// @param BreaksHint True when B is already assigned to its preferred register.
bool DefaultEvictionAdvisor::shouldEvict(const LiveInterval &A, bool IsHint,
                                         const LiveInterval &B,
                                         bool BreaksHint) const { … }

/// canEvictHintInterference - return true if the interference for VirtReg
/// on the PhysReg, which is VirtReg's hint, can be evicted in favor of VirtReg.
bool DefaultEvictionAdvisor::canEvictHintInterference(
    const LiveInterval &VirtReg, MCRegister PhysReg,
    const SmallVirtRegSet &FixedRegisters) const { … }

/// canEvictInterferenceBasedOnCost - Return true if all interferences between
/// VirtReg and PhysReg can be evicted.
///
/// @param VirtReg Live range that is about to be assigned.
/// @param PhysReg Desired register for assignment.
/// @param IsHint  True when PhysReg is VirtReg's preferred register.
/// @param MaxCost Only look for cheaper candidates and update with new cost
///                when returning true.
/// @returns True when interference can be evicted cheaper than MaxCost.
bool DefaultEvictionAdvisor::canEvictInterferenceBasedOnCost(
    const LiveInterval &VirtReg, MCRegister PhysReg, bool IsHint,
    EvictionCost &MaxCost, const SmallVirtRegSet &FixedRegisters) const { … }

MCRegister DefaultEvictionAdvisor::tryFindEvictionCandidate(
    const LiveInterval &VirtReg, const AllocationOrder &Order,
    uint8_t CostPerUseLimit, const SmallVirtRegSet &FixedRegisters) const { … }