githubmirror/julia

src/llvm-codegen-shared.h
518 строк17 KB
Sam Schweigel
codegen: relaxed jl_tls_states_t.safepoint load (#58828)
27 июн 2025, 23:38
27 июн 2025, 23:38d48a675
// This file is a part of Julia. License is MIT: https://julialang.org/license

#include <optional>
#include <utility>
#include <llvm/ADT/ArrayRef.h>
#include <llvm/ADT/SmallVector.h>
#include <llvm/Support/Debug.h>
#include <llvm/IR/Attributes.h>
#include <llvm/IR/DebugLoc.h>
#include <llvm/IR/IRBuilder.h>
#include <llvm/IR/MDBuilder.h>
#include <llvm/Support/ModRef.h>

#include "julia.h"

static constexpr std::nullopt_t None = std::nullopt;

enum AddressSpace {
    Generic = 0,
    Tracked = 10,
    Derived = 11,
    CalleeRooted = 12,
    Loaded = 13,
    FirstSpecial = Tracked,
    LastSpecial = Loaded,
};

namespace JuliaType {
    static inline llvm::StructType* get_jlvalue_ty(llvm::LLVMContext &C) {
        return llvm::StructType::get(C);
    }

    static inline llvm::PointerType* get_pjlvalue_ty(llvm::LLVMContext &C, unsigned addressSpace=0) {
        return llvm::PointerType::get(C, addressSpace);
    }

    static inline llvm::PointerType* get_prjlvalue_ty(llvm::LLVMContext &C) {
        return llvm::PointerType::get(C, AddressSpace::Tracked);
    }

    static inline llvm::PointerType* get_ppjlvalue_ty(llvm::LLVMContext &C) {
        return llvm::PointerType::get(C, 0);
    }

    static inline llvm::PointerType* get_pprjlvalue_ty(llvm::LLVMContext &C) {
        return llvm::PointerType::get(C, 0);
    }

    static inline auto get_jlfunc_ty(llvm::LLVMContext &C) {
        auto T_prjlvalue = get_prjlvalue_ty(C);
        auto T_pprjlvalue = llvm::PointerType::get(C, 0);
        return llvm::FunctionType::get(T_prjlvalue, {
                T_prjlvalue, // function
                T_pprjlvalue, // args[]
                llvm::Type::getInt32Ty(C)}, // nargs
            false);
    }

    static inline auto get_jlfunc2_ty(llvm::LLVMContext &C) {
        auto T_prjlvalue = get_prjlvalue_ty(C);
        auto T_pprjlvalue = llvm::PointerType::get(C, 0);
        return llvm::FunctionType::get(T_prjlvalue, {
                T_prjlvalue, // function
                T_pprjlvalue, // args[]
                llvm::Type::getInt32Ty(C), // nargs
                T_prjlvalue}, // linfo
            false);
    }

    static inline auto get_jlfunc3_ty(llvm::LLVMContext &C) {
        auto T_prjlvalue = get_prjlvalue_ty(C);
        auto T_pprjlvalue = llvm::PointerType::get(C, 0);
        auto T = get_pjlvalue_ty(C, Derived);
        return llvm::FunctionType::get(T_prjlvalue, {
                T, // function
                T_pprjlvalue, // args[]
                llvm::Type::getInt32Ty(C)}, // nargs
            false);
    }

    static inline auto get_jlfuncparams_ty(llvm::LLVMContext &C) {
        auto T_prjlvalue = get_prjlvalue_ty(C);
        auto T_pprjlvalue = llvm::PointerType::get(C, 0);
        return llvm::FunctionType::get(T_prjlvalue, {
                T_prjlvalue, // function
                T_pprjlvalue, // args[]
                llvm::Type::getInt32Ty(C), // nargs
                T_prjlvalue}, // linfo->sparam_vals
            false);
    }

    static inline auto get_voidfunc_ty(llvm::LLVMContext &C) {
        return llvm::FunctionType::get(llvm::Type::getVoidTy(C), /*isVarArg*/false);
    }
}

// return how many Tracked pointers are in T (count > 0),
// and if there is anything else in T (all == false)
struct CountTrackedPointers {
    unsigned count = 0;
    bool all = true;
    bool derived = false;
    CountTrackedPointers(llvm::Type *T, bool ignore_loaded=false);
};

llvm::SmallVector<llvm::Value*, 0> ExtractTrackedValues(llvm::Value *Src, llvm::Type *STy, bool isptr, llvm::IRBuilder<> &irbuilder, llvm::ArrayRef<unsigned> perm_offsets={});

static inline void llvm_dump(llvm::Value *v)
{
    v->print(llvm::dbgs(), true);
    llvm::dbgs() << "\n";
}

static inline void llvm_dump(llvm::Type *v)
{
    v->print(llvm::dbgs(), true);
    llvm::dbgs() << "\n";
}

static inline void llvm_dump(llvm::Function *f)
{
    f->print(llvm::dbgs(), nullptr, false, true);
}

static inline void llvm_dump(llvm::Module *m)
{
    m->print(llvm::dbgs(), nullptr);
}

static inline void llvm_dump(llvm::Metadata *m)
{
    m->print(llvm::dbgs());
    llvm::dbgs() << "\n";
}

static inline void llvm_dump(llvm::DebugLoc *dbg)
{
    dbg->print(llvm::dbgs());
    llvm::dbgs() << "\n";
}

static inline std::pair<llvm::MDNode*,llvm::MDNode*> tbaa_make_child_with_context(llvm::LLVMContext &ctxt, const char *name, llvm::MDNode *parent=nullptr, bool isConstant=false)
{
    llvm::MDBuilder mbuilder(ctxt);
    llvm::MDNode *jtbaa = mbuilder.createTBAARoot("jtbaa");
    llvm::MDNode *tbaa_root = mbuilder.createTBAAScalarTypeNode("jtbaa", jtbaa);
    llvm::MDNode *scalar = mbuilder.createTBAAScalarTypeNode(name, parent ? parent : tbaa_root);
    llvm::MDNode *n = mbuilder.createTBAAStructTagNode(scalar, scalar, 0, isConstant);
    return std::make_pair(n, scalar);
}

static inline llvm::MDNode *get_tbaa_const(llvm::LLVMContext &ctxt) {
    return tbaa_make_child_with_context(ctxt, "jtbaa_const", nullptr, true).first;
}

static inline llvm::Instruction *tbaa_decorate(llvm::MDNode *md, llvm::Instruction *inst)
{
    using namespace llvm;
    inst->setMetadata(llvm::LLVMContext::MD_tbaa, md);
    if (llvm::isa<llvm::LoadInst>(inst) && md && md == get_tbaa_const(md->getContext())) {
        inst->setMetadata(llvm::LLVMContext::MD_invariant_load, llvm::MDNode::get(md->getContext(), std::nullopt));
    }
    return inst;
}

// Get PTLS through current task.
static inline llvm::Value *get_current_task_from_pgcstack(llvm::IRBuilder<> &builder, llvm::Value *pgcstack)
{
    using namespace llvm;
    auto i8 = builder.getInt8Ty();
    const int pgcstack_offset = offsetof(jl_task_t, gcstack);
    return builder.CreateConstInBoundsGEP1_32(i8, pgcstack, -pgcstack_offset, "current_task");
}

// Get PTLS through current task.
static inline llvm::Value *get_current_ptls_from_task(llvm::IRBuilder<> &builder, llvm::Value *current_task, llvm::MDNode *tbaa)
{
    using namespace llvm;
    auto i8 = builder.getInt8Ty();
    auto T_ptr = builder.getPtrTy();
    const int ptls_offset = offsetof(jl_task_t, ptls);
    llvm::Value *pptls = builder.CreateConstInBoundsGEP1_32(i8, current_task, ptls_offset, "ptls_field");
    LoadInst *ptls_load = builder.CreateAlignedLoad(T_ptr, pptls, Align(sizeof(void *)), "ptls_load");
    // Note: Corresponding store (`t->ptls = ptls`) happens in `ctx_switch` of tasks.c.
    tbaa_decorate(tbaa, ptls_load);
    return ptls_load;
}

// Get signal page through current task.
static inline llvm::Value *get_current_signal_page_from_ptls(llvm::IRBuilder<> &builder, llvm::Value *ptls, llvm::MDNode *tbaa)
{
    using namespace llvm;
    // return builder.CreateCall(prepare_call(reuse_signal_page_func));
    auto T_ptr = builder.getPtrTy();
    auto i8 = builder.getInt8Ty();
    int nthfield = offsetof(jl_tls_states_t, safepoint);
    llvm::Value *psafepoint = builder.CreateConstInBoundsGEP1_32(i8, ptls, nthfield);
    LoadInst *ptls_load = builder.CreateAlignedLoad(
            T_ptr, psafepoint, Align(sizeof(void *)), "safepoint");
    ptls_load->setOrdering(AtomicOrdering::Monotonic);
    tbaa_decorate(tbaa, ptls_load);
    return ptls_load;
}

static inline void emit_signal_fence(llvm::IRBuilder<> &builder)
{
    using namespace llvm;
    builder.CreateFence(AtomicOrdering::SequentiallyConsistent, SyncScope::SingleThread);
}

static inline void emit_gc_safepoint(llvm::IRBuilder<> &builder, llvm::Type *T_size, llvm::Value *ptls, llvm::MDNode *tbaa, bool final = false)
{
    using namespace llvm;
    llvm::Value *signal_page = get_current_signal_page_from_ptls(builder, ptls, tbaa);
    emit_signal_fence(builder);
    Module *M = builder.GetInsertBlock()->getModule();
    LLVMContext &C = builder.getContext();
    // inline jlsafepoint_func->realize(M)
    if (final) {
        builder.CreateLoad(T_size, signal_page, true);
    }
    else {
        Function *F = M->getFunction("julia.safepoint");
        if (!F) {
            FunctionType *FT = FunctionType::get(Type::getVoidTy(C), {PointerType::getUnqual(T_size->getContext())}, false);
            F = Function::Create(FT, Function::ExternalLinkage, "julia.safepoint", M);
            F->setMemoryEffects(MemoryEffects::inaccessibleOrArgMemOnly());
        }
        builder.CreateCall(F, {signal_page});
    }
    emit_signal_fence(builder);
}

static inline llvm::Value *emit_gc_state_set(llvm::IRBuilder<> &builder, llvm::Type *T_size, llvm::Value *ptls, llvm::Value *state, llvm::Value *old_state, bool final)
{
    using namespace llvm;
    Type *T_int8 = state->getType();
    unsigned offset = offsetof(jl_tls_states_t, gc_state);
    Value *gc_state = builder.CreateConstInBoundsGEP1_32(T_int8, ptls, offset, "gc_state");
    if (old_state == nullptr) {
        old_state = builder.CreateLoad(T_int8, gc_state, "old_state");
        cast<LoadInst>(old_state)->setOrdering(AtomicOrdering::Monotonic);
    }
    builder.CreateAlignedStore(state, gc_state, Align(sizeof(void*)))->setOrdering(AtomicOrdering::Release);
    if (auto *C = dyn_cast<ConstantInt>(old_state))
        if (auto *C2 = dyn_cast<ConstantInt>(state))
            if (C->getZExtValue() == C2->getZExtValue())
                return old_state;
    BasicBlock *passBB = BasicBlock::Create(builder.getContext(), "safepoint", builder.GetInsertBlock()->getParent());
    BasicBlock *exitBB = BasicBlock::Create(builder.getContext(), "after_safepoint", builder.GetInsertBlock()->getParent());
    builder.CreateCondBr(builder.CreateICmpEQ(old_state, state, "is_new_state"), // Safepoint whenever we change the GC state
                         passBB, exitBB);
    builder.SetInsertPoint(passBB);
    MDNode *tbaa = get_tbaa_const(builder.getContext());
    emit_gc_safepoint(builder, T_size, ptls, tbaa, final);
    builder.CreateBr(exitBB);
    builder.SetInsertPoint(exitBB);
    return old_state;
}

static inline llvm::Value *emit_gc_unsafe_enter(llvm::IRBuilder<> &builder, llvm::Type *T_size, llvm::Value *ptls, bool final)
{
    using namespace llvm;
    Value *state = builder.getInt8(0);
    return emit_gc_state_set(builder, T_size, ptls, state, nullptr, final);
}

static inline llvm::Value *emit_gc_unsafe_leave(llvm::IRBuilder<> &builder, llvm::Type *T_size, llvm::Value *ptls, llvm::Value *state, bool final)
{
    using namespace llvm;
    Value *old_state = builder.getInt8(JL_GC_STATE_UNSAFE);
    return emit_gc_state_set(builder, T_size, ptls, state, old_state, final);
}

static inline llvm::Value *emit_gc_safe_enter(llvm::IRBuilder<> &builder, llvm::Type *T_size, llvm::Value *ptls, bool final)
{
    using namespace llvm;
    Value *state = builder.getInt8(JL_GC_STATE_SAFE);
    return emit_gc_state_set(builder, T_size, ptls, state, nullptr, final);
}

static inline llvm::Value *emit_gc_safe_leave(llvm::IRBuilder<> &builder, llvm::Type *T_size, llvm::Value *ptls, llvm::Value *state, bool final)
{
    using namespace llvm;
    Value *old_state = builder.getInt8(JL_GC_STATE_SAFE);
    return emit_gc_state_set(builder, T_size, ptls, state, old_state, final);
}

// Compatibility shims for LLVM attribute APIs that were renamed in LLVM 14.
//
// Once we no longer support LLVM < 14, these can be mechanically removed by
// translating foo(Bar, …) into Bar->foo(…) resp. Bar.foo(…).
namespace {
using namespace llvm;

inline void addFnAttr(CallInst *Target, Attribute::AttrKind Attr)
{
    Target->addFnAttr(Attr);
}

template<class T, class A>
inline void addRetAttr(T *Target, A Attr)
{
    Target->addRetAttr(Attr);
}

inline void addAttributeAtIndex(Function *F, unsigned Index, Attribute Attr)
{
    F->addAttributeAtIndex(Index, Attr);
}

inline AttributeSet getFnAttrs(const AttributeList &Attrs)
{
    return Attrs.getFnAttrs();
}

inline AttributeSet getRetAttrs(const AttributeList &Attrs)
{
    return Attrs.getRetAttrs();
}

inline bool hasFnAttr(const AttributeList &L, Attribute::AttrKind Kind)
{
    return L.hasFnAttr(Kind);
}

inline AttributeList addAttributeAtIndex(const AttributeList &L, LLVMContext &C,
                                         unsigned Index, Attribute::AttrKind Kind)
{
    return L.addAttributeAtIndex(C, Index, Kind);
}

inline AttributeList addAttributeAtIndex(const AttributeList &L, LLVMContext &C,
                                         unsigned Index, Attribute Attr)
{
    return L.addAttributeAtIndex(C, Index, Attr);
}

inline AttributeList addAttributesAtIndex(const AttributeList &L, LLVMContext &C,
                                          unsigned Index, const AttrBuilder &Builder)
{
    return L.addAttributesAtIndex(C, Index, Builder);
}

inline AttributeList addFnAttribute(const AttributeList &L, LLVMContext &C,
                                    Attribute::AttrKind Kind)
{
    return L.addFnAttribute(C, Kind);
}

inline AttributeList addRetAttribute(const AttributeList &L, LLVMContext &C,
                                     Attribute::AttrKind Kind)
{
    return L.addRetAttribute(C, Kind);
}

inline bool hasAttributesAtIndex(const AttributeList &L, unsigned Index)
{
    return L.hasAttributesAtIndex(Index);
}

inline Attribute getAttributeAtIndex(const AttributeList &L, unsigned Index, Attribute::AttrKind Kind)
{
    return L.getAttributeAtIndex(Index, Kind);
}

// Iterate through uses of a particular type.
// Recursively scan through `ConstantExpr` and `ConstantAggregate` use.
template<typename U>
struct ConstantUses {
    template<typename T>
    struct Info {
        llvm::Use *use;
        T *val;
        // If `samebits == true`, the offset the original value appears in the constant.
        size_t offset;
        // This specify whether the original value appears in the current value in exactly
        // the same bit pattern (with possibly an offset determined by `offset`).
        bool samebits;
        Info(llvm::Use *use, T *val, size_t offset, bool samebits) :
            use(use),
            val(val),
            offset(offset),
            samebits(samebits)
        {
        }
        Info(llvm::Use *use, size_t offset, bool samebits) :
            use(use),
            val(cast<T>(use->getUser())),
            offset(offset),
            samebits(samebits)
        {
        }
    };
    using UseInfo = Info<U>;
    struct Frame : Info<llvm::Constant> {
        template<typename... Args>
        Frame(Args &&... args) :
            Info<llvm::Constant>(std::forward<Args>(args)...),
            cur(this->val->use_empty() ? nullptr : &*this->val->use_begin()),
            _next(cur ? cur->getNext() : nullptr)
        {
        }
    private:
        void next()
        {
            cur = _next;
            if (!cur)
                return;
            _next = cur->getNext();
        }
        llvm::Use *cur;
        llvm::Use *_next;
        friend struct ConstantUses;
    };
    ConstantUses(llvm::Constant *c, llvm::Module &M)
        : stack{Frame(nullptr, c, 0u, true)},
          M(M)
    {
        forward();
    }
    UseInfo get_info() const
    {
        auto &top = stack.back();
        return UseInfo(top.cur, top.offset, top.samebits);
    }
    const auto &get_stack() const
    {
        return stack;
    }
    void next()
    {
        stack.back().next();
        forward();
    }
    bool done()
    {
        return stack.empty();
    }
private:
    void forward();
    llvm::SmallVector<Frame, 4> stack;
    llvm::Module &M;
};

template<typename U>
void ConstantUses<U>::forward()
{
    assert(!stack.empty());
    auto frame = &stack.back();
    const auto &DL = M.getDataLayout();
    auto pop = [&] {
        stack.pop_back();
        if (stack.empty()) {
            return false;
        }
        frame = &stack.back();
        return true;
    };
    auto push = [&] (llvm::Use *use, llvm::Constant *c, size_t offset, bool samebits) {
        stack.emplace_back(use, c, offset, samebits);
        frame = &stack.back();
    };
    auto handle_constaggr = [&] (llvm::Use *use, llvm::ConstantAggregate *aggr) {
        if (!frame->samebits) {
            push(use, aggr, 0, false);
            return;
        }
        if (auto strct = dyn_cast<llvm::ConstantStruct>(aggr)) {
            auto layout = DL.getStructLayout(strct->getType());
            push(use, strct, frame->offset + layout->getElementOffset(use->getOperandNo()), true);
        }
        else if (auto ary = dyn_cast<llvm::ConstantArray>(aggr)) {
            auto elty = ary->getType()->getElementType();
            push(use, ary, frame->offset + DL.getTypeAllocSize(elty) * use->getOperandNo(), true);
        }
        else if (auto vec = dyn_cast<llvm::ConstantVector>(aggr)) {
            auto elty = vec->getType()->getElementType();
            push(use, vec, frame->offset + DL.getTypeAllocSize(elty) * use->getOperandNo(), true);
        }
        else {
            abort();
        }
    };
    auto handle_constexpr = [&] (llvm::Use *use, llvm::ConstantExpr *expr) {
        if (!frame->samebits) {
            push(use, expr, 0, false);
            return;
        }
        auto opcode = expr->getOpcode();
        if (opcode == llvm::Instruction::PtrToInt || opcode == llvm::Instruction::IntToPtr ||
            opcode == llvm::Instruction::AddrSpaceCast || opcode == llvm::Instruction::BitCast) {
            push(use, expr, frame->offset, true);
        }
        else {
            push(use, expr, 0, false);
        }
    };
    while (true) {
        auto use = frame->cur;
        if (!use) {
            if (!pop())
                return;
            continue;
        }
        auto user = use->getUser();
        if (isa<U>(user))
            return;
        frame->next();
        if (auto aggr = dyn_cast<llvm::ConstantAggregate>(user)) {
            handle_constaggr(use, aggr);
        }
        else if (auto expr = dyn_cast<llvm::ConstantExpr>(user)) {
            handle_constexpr(use, expr);
        }
    }
}
}