llvmjit.c

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/*-------------------------------------------------------------------------
 *
 * llvmjit.c
 *    Core part of the LLVM JIT provider.
 *
 * Copyright (c) 2016-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/jit/llvm/llvmjit.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <llvm-c/Analysis.h>
#include <llvm-c/BitReader.h>
#include <llvm-c/BitWriter.h>
#include <llvm-c/Core.h>
#include <llvm-c/ExecutionEngine.h>
#include <llvm-c/OrcBindings.h>
#include <llvm-c/Support.h>
#include <llvm-c/Target.h>
#include <llvm-c/Transforms/IPO.h>
#include <llvm-c/Transforms/PassManagerBuilder.h>
#include <llvm-c/Transforms/Scalar.h>
#if LLVM_VERSION_MAJOR > 6
#include <llvm-c/Transforms/Utils.h>
#endif

#include "jit/llvmjit.h"
#include "jit/llvmjit_emit.h"
#include "miscadmin.h"
#include "portability/instr_time.h"
#include "storage/ipc.h"
#include "utils/memutils.h"
#include "utils/resowner_private.h"

/* Handle of a module emitted via ORC JIT */
typedef struct LLVMJitHandle
{
    LLVMOrcJITStackRef stack;
    LLVMOrcModuleHandle orc_handle;
} LLVMJitHandle;


/* types & functions commonly needed for JITing */
LLVMTypeRef TypeSizeT;
LLVMTypeRef TypeParamBool;
LLVMTypeRef TypeStorageBool;
LLVMTypeRef TypePGFunction;
LLVMTypeRef StructNullableDatum;
LLVMTypeRef StructHeapTupleFieldsField3;
LLVMTypeRef StructHeapTupleFields;
LLVMTypeRef StructHeapTupleHeaderData;
LLVMTypeRef StructHeapTupleDataChoice;
LLVMTypeRef StructHeapTupleData;
LLVMTypeRef StructMinimalTupleData;
LLVMTypeRef StructItemPointerData;
LLVMTypeRef StructBlockId;
LLVMTypeRef StructFormPgAttribute;
LLVMTypeRef StructTupleConstr;
LLVMTypeRef StructTupleDescData;
LLVMTypeRef StructTupleTableSlot;
LLVMTypeRef StructHeapTupleTableSlot;
LLVMTypeRef StructMinimalTupleTableSlot;
LLVMTypeRef StructMemoryContextData;
LLVMTypeRef StructPGFinfoRecord;
LLVMTypeRef StructFmgrInfo;
LLVMTypeRef StructFunctionCallInfoData;
LLVMTypeRef StructExprContext;
LLVMTypeRef StructExprEvalStep;
LLVMTypeRef StructExprState;
LLVMTypeRef StructAggState;
LLVMTypeRef StructAggStatePerGroupData;
LLVMTypeRef StructAggStatePerTransData;

LLVMValueRef AttributeTemplate;
LLVMValueRef FuncStrlen;
LLVMValueRef FuncVarsizeAny;
LLVMValueRef FuncSlotGetsomeattrsInt;
LLVMValueRef FuncSlotGetmissingattrs;
LLVMValueRef FuncMakeExpandedObjectReadOnlyInternal;
LLVMValueRef FuncExecEvalSubscriptingRef;
LLVMValueRef FuncExecEvalSysVar;
LLVMValueRef FuncExecAggTransReparent;
LLVMValueRef FuncExecAggInitGroup;


static bool llvm_session_initialized = false;
static size_t llvm_generation = 0;
static const char *llvm_triple = NULL;
static const char *llvm_layout = NULL;


static LLVMTargetMachineRef llvm_opt0_targetmachine;
static LLVMTargetMachineRef llvm_opt3_targetmachine;

static LLVMTargetRef llvm_targetref;
static LLVMOrcJITStackRef llvm_opt0_orc;
static LLVMOrcJITStackRef llvm_opt3_orc;


static void llvm_release_context(JitContext *context);
static void llvm_session_initialize(void);
static void llvm_shutdown(int code, Datum arg);
static void llvm_compile_module(LLVMJitContext *context);
static void llvm_optimize_module(LLVMJitContext *context, LLVMModuleRef module);

static void llvm_create_types(void);
static uint64_t llvm_resolve_symbol(const char *name, void *ctx);


PG_MODULE_MAGIC;


/*
 * Initialize LLVM JIT provider.
 */
void
_PG_jit_provider_init(JitProviderCallbacks *cb)
{
    cb->reset_after_error = llvm_reset_after_error;
    cb->release_context = llvm_release_context;
    cb->compile_expr = llvm_compile_expr;
}

/*
 * Create a context for JITing work.
 *
 * The context, including subsidiary resources, will be cleaned up either when
 * the context is explicitly released, or when the lifetime of
 * CurrentResourceOwner ends (usually the end of the current [sub]xact).
 */
LLVMJitContext *
llvm_create_context(int jitFlags)
{
    LLVMJitContext *context;

    llvm_assert_in_fatal_section();

    llvm_session_initialize();

    ResourceOwnerEnlargeJIT(CurrentResourceOwner);

    context = MemoryContextAllocZero(TopMemoryContext,
                                     sizeof(LLVMJitContext));
    context->base.flags = jitFlags;

    /* ensure cleanup */
    context->base.resowner = CurrentResourceOwner;
    ResourceOwnerRememberJIT(CurrentResourceOwner, PointerGetDatum(context));

    return context;
}

/*
 * Release resources required by one llvm context.
 */
static void
llvm_release_context(JitContext *context)
{
    LLVMJitContext *llvm_context = (LLVMJitContext *) context;

    llvm_enter_fatal_on_oom();

    /*
     * When this backend is exiting, don't clean up LLVM. As an error might
     * have occurred from within LLVM, we do not want to risk reentering. All
     * resource cleanup is going to happen through process exit.
     */
    if (!proc_exit_inprogress)
    {
        if (llvm_context->module)
        {
            LLVMDisposeModule(llvm_context->module);
            llvm_context->module = NULL;
        }

        while (llvm_context->handles != NIL)
        {
            LLVMJitHandle *jit_handle;

            jit_handle = (LLVMJitHandle *) linitial(llvm_context->handles);
            llvm_context->handles = list_delete_first(llvm_context->handles);

            LLVMOrcRemoveModule(jit_handle->stack, jit_handle->orc_handle);
            pfree(jit_handle);
        }
    }
}

/*
 * Return module which may be modified, e.g. by creating new functions.
 */
LLVMModuleRef
llvm_mutable_module(LLVMJitContext *context)
{
    llvm_assert_in_fatal_section();

    /*
     * If there's no in-progress module, create a new one.
     */
    if (!context->module)
    {
        context->compiled = false;
        context->module_generation = llvm_generation++;
        context->module = LLVMModuleCreateWithName("pg");
        LLVMSetTarget(context->module, llvm_triple);
        LLVMSetDataLayout(context->module, llvm_layout);
    }

    return context->module;
}

/*
 * Expand function name to be non-conflicting. This should be used by code
 * generating code, when adding new externally visible function definitions to
 * a Module.
 */
char *
llvm_expand_funcname(struct LLVMJitContext *context, const char *basename)
{
    Assert(context->module != NULL);

    context->base.instr.created_functions++;

    /*
     * Previously we used dots to separate, but turns out some tools, e.g.
     * GDB, don't like that and truncate name.
     */
    return psprintf("%s_%zu_%d",
                    basename,
                    context->module_generation,
                    context->counter++);
}

/*
 * Return pointer to function funcname, which has to exist. If there's pending
 * code to be optimized and emitted, do so first.
 */
void *
llvm_get_function(LLVMJitContext *context, const char *funcname)
{
    LLVMOrcTargetAddress addr = 0;
#if defined(HAVE_DECL_LLVMORCGETSYMBOLADDRESSIN) && HAVE_DECL_LLVMORCGETSYMBOLADDRESSIN
    ListCell   *lc;
#endif

    llvm_assert_in_fatal_section();

    /*
     * If there is a pending / not emitted module, compile and emit now.
     * Otherwise we might not find the [correct] function.
     */
    if (!context->compiled)
    {
        llvm_compile_module(context);
    }

    /*
     * ORC's symbol table is of *unmangled* symbols. Therefore we don't need
     * to mangle here.
     */

#if defined(HAVE_DECL_LLVMORCGETSYMBOLADDRESSIN) && HAVE_DECL_LLVMORCGETSYMBOLADDRESSIN
    foreach(lc, context->handles)
    {
        LLVMJitHandle *handle = (LLVMJitHandle *) lfirst(lc);

        addr = 0;
        if (LLVMOrcGetSymbolAddressIn(handle->stack, &addr, handle->orc_handle, funcname))
            elog(ERROR, "failed to look up symbol \"%s\"", funcname);
        if (addr)
            return (void *) (uintptr_t) addr;
    }

#else

#if LLVM_VERSION_MAJOR < 5
    if ((addr = LLVMOrcGetSymbolAddress(llvm_opt0_orc, funcname)))
        return (void *) (uintptr_t) addr;
    if ((addr = LLVMOrcGetSymbolAddress(llvm_opt3_orc, funcname)))
        return (void *) (uintptr_t) addr;
#else
    if (LLVMOrcGetSymbolAddress(llvm_opt0_orc, &addr, funcname))
        elog(ERROR, "failed to look up symbol \"%s\"", funcname);
    if (addr)
        return (void *) (uintptr_t) addr;
    if (LLVMOrcGetSymbolAddress(llvm_opt3_orc, &addr, funcname))
        elog(ERROR, "failed to look up symbol \"%s\"", funcname);
    if (addr)
        return (void *) (uintptr_t) addr;
#endif                          /* LLVM_VERSION_MAJOR */

#endif                          /* HAVE_DECL_LLVMORCGETSYMBOLADDRESSIN */

    elog(ERROR, "failed to JIT: %s", funcname);

    return NULL;
}

/*
 * Return declaration for passed function, adding it to the module if
 * necessary.
 *
 * This is used to make functions imported by llvm_create_types() known to the
 * module that's currently being worked on.
 */
LLVMValueRef
llvm_get_decl(LLVMModuleRef mod, LLVMValueRef v_src)
{
    LLVMValueRef v_fn;

    /* don't repeatedly add function */
    v_fn = LLVMGetNamedFunction(mod, LLVMGetValueName(v_src));
    if (v_fn)
        return v_fn;

    v_fn = LLVMAddFunction(mod,
                           LLVMGetValueName(v_src),
                           LLVMGetElementType(LLVMTypeOf(v_src)));
    llvm_copy_attributes(v_src, v_fn);

    return v_fn;
}

/*
 * Copy attributes from one function to another.
 */
void
llvm_copy_attributes(LLVMValueRef v_from, LLVMValueRef v_to)
{
    int         num_attributes;
    int         attno;
    LLVMAttributeRef *attrs;

    num_attributes =
        LLVMGetAttributeCountAtIndex(v_from, LLVMAttributeFunctionIndex);

    attrs = palloc(sizeof(LLVMAttributeRef) * num_attributes);
    LLVMGetAttributesAtIndex(v_from, LLVMAttributeFunctionIndex, attrs);

    for (attno = 0; attno < num_attributes; attno++)
    {
        LLVMAddAttributeAtIndex(v_to, LLVMAttributeFunctionIndex,
                                attrs[attno]);
    }
}

/*
 * Return a callable LLVMValueRef for fcinfo.
 */
LLVMValueRef
llvm_function_reference(LLVMJitContext *context,
                        LLVMBuilderRef builder,
                        LLVMModuleRef mod,
                        FunctionCallInfo fcinfo)
{
    char       *modname;
    char       *basename;
    char       *funcname;

    LLVMValueRef v_fn;

    fmgr_symbol(fcinfo->flinfo->fn_oid, &modname, &basename);

    if (modname != NULL && basename != NULL)
    {
        /* external function in loadable library */
        funcname = psprintf("pgextern.%s.%s", modname, basename);
    }
    else if (basename != NULL)
    {
        /* internal function */
        funcname = psprintf("%s", basename);
    }
    else
    {
        /*
         * Function we don't know to handle, return pointer. We do so by
         * creating a global constant containing a pointer to the function.
         * Makes IR more readable.
         */
        LLVMValueRef v_fn_addr;

        funcname = psprintf("pgoidextern.%u",
                            fcinfo->flinfo->fn_oid);
        v_fn = LLVMGetNamedGlobal(mod, funcname);
        if (v_fn != 0)
            return LLVMBuildLoad(builder, v_fn, "");

        v_fn_addr = l_ptr_const(fcinfo->flinfo->fn_addr, TypePGFunction);

        v_fn = LLVMAddGlobal(mod, TypePGFunction, funcname);
        LLVMSetInitializer(v_fn, v_fn_addr);
        LLVMSetGlobalConstant(v_fn, true);

        return LLVMBuildLoad(builder, v_fn, "");
    }

    /* check if function already has been added */
    v_fn = LLVMGetNamedFunction(mod, funcname);
    if (v_fn != 0)
        return v_fn;

    v_fn = LLVMAddFunction(mod, funcname, LLVMGetElementType(TypePGFunction));

    return v_fn;
}

/*
 * Optimize code in module using the flags set in context.
 */
static void
llvm_optimize_module(LLVMJitContext *context, LLVMModuleRef module)
{
    LLVMPassManagerBuilderRef llvm_pmb;
    LLVMPassManagerRef llvm_mpm;
    LLVMPassManagerRef llvm_fpm;
    LLVMValueRef func;
    int         compile_optlevel;

    if (context->base.flags & PGJIT_OPT3)
        compile_optlevel = 3;
    else
        compile_optlevel = 0;

    /*
     * Have to create a new pass manager builder every pass through, as the
     * inliner has some per-builder state. Otherwise one ends up only inlining
     * a function the first time though.
     */
    llvm_pmb = LLVMPassManagerBuilderCreate();
    LLVMPassManagerBuilderSetOptLevel(llvm_pmb, compile_optlevel);
    llvm_fpm = LLVMCreateFunctionPassManagerForModule(module);

    if (context->base.flags & PGJIT_OPT3)
    {
        /* TODO: Unscientifically determined threshold */
        LLVMPassManagerBuilderUseInlinerWithThreshold(llvm_pmb, 512);
    }
    else
    {
        /* we rely on mem2reg heavily, so emit even in the O0 case */
        LLVMAddPromoteMemoryToRegisterPass(llvm_fpm);
    }

    LLVMPassManagerBuilderPopulateFunctionPassManager(llvm_pmb, llvm_fpm);

    /*
     * Do function level optimization. This could be moved to the point where
     * functions are emitted, to reduce memory usage a bit.
     */
    LLVMInitializeFunctionPassManager(llvm_fpm);
    for (func = LLVMGetFirstFunction(context->module);
         func != NULL;
         func = LLVMGetNextFunction(func))
        LLVMRunFunctionPassManager(llvm_fpm, func);
    LLVMFinalizeFunctionPassManager(llvm_fpm);
    LLVMDisposePassManager(llvm_fpm);

    /*
     * Perform module level optimization. We do so even in the non-optimized
     * case, so always-inline functions etc get inlined. It's cheap enough.
     */
    llvm_mpm = LLVMCreatePassManager();
    LLVMPassManagerBuilderPopulateModulePassManager(llvm_pmb,
                                                    llvm_mpm);
    /* always use always-inliner pass */
    if (!(context->base.flags & PGJIT_OPT3))
        LLVMAddAlwaysInlinerPass(llvm_mpm);
    /* if doing inlining, but no expensive optimization, add inlining pass */
    if (context->base.flags & PGJIT_INLINE
        && !(context->base.flags & PGJIT_OPT3))
        LLVMAddFunctionInliningPass(llvm_mpm);
    LLVMRunPassManager(llvm_mpm, context->module);
    LLVMDisposePassManager(llvm_mpm);

    LLVMPassManagerBuilderDispose(llvm_pmb);
}

/*
 * Emit code for the currently pending module.
 */
static void
llvm_compile_module(LLVMJitContext *context)
{
    LLVMOrcModuleHandle orc_handle;
    MemoryContext oldcontext;
    static LLVMOrcJITStackRef compile_orc;
    instr_time  starttime;
    instr_time  endtime;

    if (context->base.flags & PGJIT_OPT3)
        compile_orc = llvm_opt3_orc;
    else
        compile_orc = llvm_opt0_orc;

    /* perform inlining */
    if (context->base.flags & PGJIT_INLINE)
    {
        INSTR_TIME_SET_CURRENT(starttime);
        llvm_inline(context->module);
        INSTR_TIME_SET_CURRENT(endtime);
        INSTR_TIME_ACCUM_DIFF(context->base.instr.inlining_counter,
                              endtime, starttime);
    }

    if (jit_dump_bitcode)
    {
        char       *filename;

        filename = psprintf("%u.%zu.bc",
                            MyProcPid,
                            context->module_generation);
        LLVMWriteBitcodeToFile(context->module, filename);
        pfree(filename);
    }


    /* optimize according to the chosen optimization settings */
    INSTR_TIME_SET_CURRENT(starttime);
    llvm_optimize_module(context, context->module);
    INSTR_TIME_SET_CURRENT(endtime);
    INSTR_TIME_ACCUM_DIFF(context->base.instr.optimization_counter,
                          endtime, starttime);

    if (jit_dump_bitcode)
    {
        char       *filename;

        filename = psprintf("%u.%zu.optimized.bc",
                            MyProcPid,
                            context->module_generation);
        LLVMWriteBitcodeToFile(context->module, filename);
        pfree(filename);
    }

    /*
     * Emit the code. Note that this can, depending on the optimization
     * settings, take noticeable resources as code emission executes low-level
     * instruction combining/selection passes etc. Without optimization a
     * faster instruction selection mechanism is used.
     */
    INSTR_TIME_SET_CURRENT(starttime);
#if LLVM_VERSION_MAJOR > 6
    {
        if (LLVMOrcAddEagerlyCompiledIR(compile_orc, &orc_handle, context->module,
                                        llvm_resolve_symbol, NULL))
        {
            elog(ERROR, "failed to JIT module");
        }

        /* LLVMOrcAddEagerlyCompiledIR takes ownership of the module */
    }
#elif LLVM_VERSION_MAJOR > 4
    {
        LLVMSharedModuleRef smod;

        smod = LLVMOrcMakeSharedModule(context->module);
        if (LLVMOrcAddEagerlyCompiledIR(compile_orc, &orc_handle, smod,
                                        llvm_resolve_symbol, NULL))
        {
            elog(ERROR, "failed to JIT module");
        }
        LLVMOrcDisposeSharedModuleRef(smod);
    }
#else                           /* LLVM 4.0 and 3.9 */
    {
        orc_handle = LLVMOrcAddEagerlyCompiledIR(compile_orc, context->module,
                                                 llvm_resolve_symbol, NULL);
        LLVMDisposeModule(context->module);
    }
#endif
    INSTR_TIME_SET_CURRENT(endtime);
    INSTR_TIME_ACCUM_DIFF(context->base.instr.emission_counter,
                          endtime, starttime);

    context->module = NULL;
    context->compiled = true;

    /* remember emitted code for cleanup and lookups */
    oldcontext = MemoryContextSwitchTo(TopMemoryContext);
    {
        LLVMJitHandle *handle;

        handle = (LLVMJitHandle *) palloc(sizeof(LLVMJitHandle));
        handle->stack = compile_orc;
        handle->orc_handle = orc_handle;

        context->handles = lappend(context->handles, handle);
    }
    MemoryContextSwitchTo(oldcontext);

    ereport(DEBUG1,
            (errmsg("time to inline: %.3fs, opt: %.3fs, emit: %.3fs",
                    INSTR_TIME_GET_DOUBLE(context->base.instr.inlining_counter),
                    INSTR_TIME_GET_DOUBLE(context->base.instr.optimization_counter),
                    INSTR_TIME_GET_DOUBLE(context->base.instr.emission_counter)),
             errhidestmt(true),
             errhidecontext(true)));
}

/*
 * Per session initialization.
 */
static void
llvm_session_initialize(void)
{
    MemoryContext oldcontext;
    char       *error = NULL;
    char       *cpu = NULL;
    char       *features = NULL;

    if (llvm_session_initialized)
        return;

    oldcontext = MemoryContextSwitchTo(TopMemoryContext);

    LLVMInitializeNativeTarget();
    LLVMInitializeNativeAsmPrinter();
    LLVMInitializeNativeAsmParser();

    /*
     * Synchronize types early, as that also includes inferring the target
     * triple.
     */
    llvm_create_types();

    if (LLVMGetTargetFromTriple(llvm_triple, &llvm_targetref, &error) != 0)
    {
        elog(FATAL, "failed to query triple %s\n", error);
    }

    /*
     * We want the generated code to use all available features. Therefore
     * grab the host CPU string and detect features of the current CPU. The
     * latter is needed because some CPU architectures default to enabling
     * features not all CPUs have (weird, huh).
     */
    cpu = LLVMGetHostCPUName();
    features = LLVMGetHostCPUFeatures();
    elog(DEBUG2, "LLVMJIT detected CPU \"%s\", with features \"%s\"",
         cpu, features);

    llvm_opt0_targetmachine =
        LLVMCreateTargetMachine(llvm_targetref, llvm_triple, cpu, features,
                                LLVMCodeGenLevelNone,
                                LLVMRelocDefault,
                                LLVMCodeModelJITDefault);
    llvm_opt3_targetmachine =
        LLVMCreateTargetMachine(llvm_targetref, llvm_triple, cpu, features,
                                LLVMCodeGenLevelAggressive,
                                LLVMRelocDefault,
                                LLVMCodeModelJITDefault);

    LLVMDisposeMessage(cpu);
    cpu = NULL;
    LLVMDisposeMessage(features);
    features = NULL;

    /* force symbols in main binary to be loaded */
    LLVMLoadLibraryPermanently(NULL);

    llvm_opt0_orc = LLVMOrcCreateInstance(llvm_opt0_targetmachine);
    llvm_opt3_orc = LLVMOrcCreateInstance(llvm_opt3_targetmachine);

#if defined(HAVE_DECL_LLVMCREATEGDBREGISTRATIONLISTENER) && HAVE_DECL_LLVMCREATEGDBREGISTRATIONLISTENER
    if (jit_debugging_support)
    {
        LLVMJITEventListenerRef l = LLVMCreateGDBRegistrationListener();

        LLVMOrcRegisterJITEventListener(llvm_opt0_orc, l);
        LLVMOrcRegisterJITEventListener(llvm_opt3_orc, l);
    }
#endif
#if defined(HAVE_DECL_LLVMCREATEPERFJITEVENTLISTENER) && HAVE_DECL_LLVMCREATEPERFJITEVENTLISTENER
    if (jit_profiling_support)
    {
        LLVMJITEventListenerRef l = LLVMCreatePerfJITEventListener();

        LLVMOrcRegisterJITEventListener(llvm_opt0_orc, l);
        LLVMOrcRegisterJITEventListener(llvm_opt3_orc, l);
    }
#endif

    before_shmem_exit(llvm_shutdown, 0);

    llvm_session_initialized = true;

    MemoryContextSwitchTo(oldcontext);
}

static void
llvm_shutdown(int code, Datum arg)
{
    /* unregister profiling support, needs to be flushed to be useful */

    if (llvm_opt3_orc)
    {
#if defined(HAVE_DECL_LLVMORCREGISTERPERF) && HAVE_DECL_LLVMORCREGISTERPERF
        if (jit_profiling_support)
            LLVMOrcUnregisterPerf(llvm_opt3_orc);
#endif
        LLVMOrcDisposeInstance(llvm_opt3_orc);
        llvm_opt3_orc = NULL;
    }

    if (llvm_opt0_orc)
    {
#if defined(HAVE_DECL_LLVMORCREGISTERPERF) && HAVE_DECL_LLVMORCREGISTERPERF
        if (jit_profiling_support)
            LLVMOrcUnregisterPerf(llvm_opt0_orc);
#endif
        LLVMOrcDisposeInstance(llvm_opt0_orc);
        llvm_opt0_orc = NULL;
    }
}

/* helper for llvm_create_types, returning a global var's type */
static LLVMTypeRef
load_type(LLVMModuleRef mod, const char *name)
{
    LLVMValueRef value;
    LLVMTypeRef typ;

    /* this'll return a *pointer* to the global */
    value = LLVMGetNamedGlobal(mod, name);
    if (!value)
        elog(ERROR, "type %s is unknown", name);

    /* therefore look at the contained type and return that */
    typ = LLVMTypeOf(value);
    Assert(typ != NULL);
    typ = LLVMGetElementType(typ);
    Assert(typ != NULL);
    return typ;
}

/* helper for llvm_create_types, returning a function's return type */
static LLVMTypeRef
load_return_type(LLVMModuleRef mod, const char *name)
{
    LLVMValueRef value;
    LLVMTypeRef typ;

    /* this'll return a *pointer* to the function */
    value = LLVMGetNamedFunction(mod, name);
    if (!value)
        elog(ERROR, "function %s is unknown", name);

    /* get type of function pointer */
    typ = LLVMTypeOf(value);
    Assert(typ != NULL);
    /* dereference pointer */
    typ = LLVMGetElementType(typ);
    Assert(typ != NULL);
    /* and look at return type */
    typ = LLVMGetReturnType(typ);
    Assert(typ != NULL);

    return typ;
}

/*
 * Load required information, types, function signatures from llvmjit_types.c
 * and make them available in global variables.
 *
 * Those global variables are then used while emitting code.
 */
static void
llvm_create_types(void)
{
    char        path[MAXPGPATH];
    LLVMMemoryBufferRef buf;
    char       *msg;
    LLVMModuleRef mod = NULL;

    snprintf(path, MAXPGPATH, "%s/%s", pkglib_path, "llvmjit_types.bc");

    /* open file */
    if (LLVMCreateMemoryBufferWithContentsOfFile(path, &buf, &msg))
    {
        elog(ERROR, "LLVMCreateMemoryBufferWithContentsOfFile(%s) failed: %s",
             path, msg);
    }

    /* eagerly load contents, going to need it all */
    if (LLVMParseBitcode2(buf, &mod))
    {
        elog(ERROR, "LLVMParseBitcode2 of %s failed", path);
    }
    LLVMDisposeMemoryBuffer(buf);

    /*
     * Load triple & layout from clang emitted file so we're guaranteed to be
     * compatible.
     */
    llvm_triple = pstrdup(LLVMGetTarget(mod));
    llvm_layout = pstrdup(LLVMGetDataLayoutStr(mod));

    TypeSizeT = load_type(mod, "TypeSizeT");
    TypeParamBool = load_return_type(mod, "FunctionReturningBool");
    TypeStorageBool = load_type(mod, "TypeStorageBool");
    TypePGFunction = load_type(mod, "TypePGFunction");
    StructNullableDatum = load_type(mod, "StructNullableDatum");
    StructExprContext = load_type(mod, "StructExprContext");
    StructExprEvalStep = load_type(mod, "StructExprEvalStep");
    StructExprState = load_type(mod, "StructExprState");
    StructFunctionCallInfoData = load_type(mod, "StructFunctionCallInfoData");
    StructMemoryContextData = load_type(mod, "StructMemoryContextData");
    StructTupleTableSlot = load_type(mod, "StructTupleTableSlot");
    StructHeapTupleTableSlot = load_type(mod, "StructHeapTupleTableSlot");
    StructMinimalTupleTableSlot = load_type(mod, "StructMinimalTupleTableSlot");
    StructHeapTupleData = load_type(mod, "StructHeapTupleData");
    StructTupleDescData = load_type(mod, "StructTupleDescData");
    StructAggState = load_type(mod, "StructAggState");
    StructAggStatePerGroupData = load_type(mod, "StructAggStatePerGroupData");
    StructAggStatePerTransData = load_type(mod, "StructAggStatePerTransData");

    AttributeTemplate = LLVMGetNamedFunction(mod, "AttributeTemplate");
    FuncStrlen = LLVMGetNamedFunction(mod, "strlen");
    FuncVarsizeAny = LLVMGetNamedFunction(mod, "varsize_any");
    FuncSlotGetsomeattrsInt = LLVMGetNamedFunction(mod, "slot_getsomeattrs_int");
    FuncSlotGetmissingattrs = LLVMGetNamedFunction(mod, "slot_getmissingattrs");
    FuncMakeExpandedObjectReadOnlyInternal = LLVMGetNamedFunction(mod, "MakeExpandedObjectReadOnlyInternal");
    FuncExecEvalSubscriptingRef = LLVMGetNamedFunction(mod, "ExecEvalSubscriptingRef");
    FuncExecEvalSysVar = LLVMGetNamedFunction(mod, "ExecEvalSysVar");
    FuncExecAggTransReparent = LLVMGetNamedFunction(mod, "ExecAggTransReparent");
    FuncExecAggInitGroup = LLVMGetNamedFunction(mod, "ExecAggInitGroup");

    /*
     * Leave the module alive, otherwise references to function would be
     * dangling.
     */
}

/*
 * Split a symbol into module / function parts.  If the function is in the
 * main binary (or an external library) *modname will be NULL.
 */
void
llvm_split_symbol_name(const char *name, char **modname, char **funcname)
{
    *modname = NULL;
    *funcname = NULL;

    /*
     * Module function names are pgextern.$module.$funcname
     */
    if (strncmp(name, "pgextern.", strlen("pgextern.")) == 0)
    {
        /*
         * Symbol names cannot contain a ., therefore we can split based on
         * first and last occurrence of one.
         */
        *funcname = rindex(name, '.');
        (*funcname)++;          /* jump over . */

        *modname = pnstrdup(name + strlen("pgextern."),
                            *funcname - name - strlen("pgextern.") - 1);
        Assert(funcname);

        *funcname = pstrdup(*funcname);
    }
    else
    {
        *modname = NULL;
        *funcname = pstrdup(name);
    }
}

/*
 * Attempt to resolve symbol, so LLVM can emit a reference to it.
 */
static uint64_t
llvm_resolve_symbol(const char *symname, void *ctx)
{
    uintptr_t   addr;
    char       *funcname;
    char       *modname;

    /*
     * macOS prefixes all object level symbols with an underscore. But neither
     * dlsym() nor PG's inliner expect that. So undo.
     */
#if defined(__darwin__)
    if (symname[0] != '_')
        elog(ERROR, "expected prefixed symbol name, but got \"%s\"", symname);
    symname++;
#endif

    llvm_split_symbol_name(symname, &modname, &funcname);

    /* functions that aren't resolved to names shouldn't ever get here */
    Assert(funcname);

    if (modname)
        addr = (uintptr_t) load_external_function(modname, funcname,
                                                  true, NULL);
    else
        addr = (uintptr_t) LLVMSearchForAddressOfSymbol(symname);

    pfree(funcname);
    if (modname)
        pfree(modname);

    /* let LLVM will error out - should never happen */
    if (!addr)
        elog(WARNING, "failed to resolve name %s", symname);

    return (uint64_t) addr;
}