xref: /third_party/rust/rust/compiler/rustc_codegen_llvm/src/context.rs

use crate::attributes;
use crate::back::write::to_llvm_code_model;
use crate::callee::get_fn;
use crate::coverageinfo;
use crate::debuginfo;
use crate::llvm;
use crate::llvm_util;
use crate::type_::Type;
use crate::value::Value;

use cstr::cstr;
use rustc_codegen_ssa::base::{wants_msvc_seh, wants_wasm_eh};
use rustc_codegen_ssa::traits::*;
use rustc_data_structures::base_n;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::small_c_str::SmallCStr;
use rustc_hir::def_id::DefId;
use rustc_middle::mir::mono::CodegenUnit;
use rustc_middle::ty::layout::{
    FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, LayoutError, LayoutOfHelpers,
    TyAndLayout,
};
use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
use rustc_middle::{bug, span_bug};
use rustc_session::config::{BranchProtection, CFGuard, CFProtection};
use rustc_session::config::{CrateType, DebugInfo, PAuthKey, PacRet};
use rustc_session::Session;
use rustc_span::source_map::Span;
use rustc_span::source_map::Spanned;
use rustc_target::abi::{
    call::FnAbi, HasDataLayout, PointeeInfo, Size, TargetDataLayout, VariantIdx,
};
use rustc_target::spec::{HasTargetSpec, RelocModel, Target, TlsModel};
use smallvec::SmallVec;

use std::cell::{Cell, RefCell};
use std::ffi::CStr;
use std::str;

/// There is one `CodegenCx` per compilation unit. Each one has its own LLVM
/// `llvm::Context` so that several compilation units may be optimized in parallel.
/// All other LLVM data structures in the `CodegenCx` are tied to that `llvm::Context`.
pub struct CodegenCx<'ll, 'tcx> {
    pub tcx: TyCtxt<'tcx>,
    pub check_overflow: bool,
    pub use_dll_storage_attrs: bool,
    pub tls_model: llvm::ThreadLocalMode,

    pub llmod: &'ll llvm::Module,
    pub llcx: &'ll llvm::Context,
    pub codegen_unit: &'tcx CodegenUnit<'tcx>,

    /// Cache instances of monomorphic and polymorphic items
    pub instances: RefCell<FxHashMap<Instance<'tcx>, &'ll Value>>,
    /// Cache generated vtables
    pub vtables:
        RefCell<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), &'ll Value>>,
    /// Cache of constant strings,
    pub const_str_cache: RefCell<FxHashMap<String, &'ll Value>>,

    /// Reverse-direction for const ptrs cast from globals.
    ///
    /// Key is a Value holding a `*T`,
    /// Val is a Value holding a `*[T]`.
    ///
    /// Needed because LLVM loses pointer->pointee association
    /// when we ptrcast, and we have to ptrcast during codegen
    /// of a `[T]` const because we form a slice, a `(*T,usize)` pair, not
    /// a pointer to an LLVM array type. Similar for trait objects.
    pub const_unsized: RefCell<FxHashMap<&'ll Value, &'ll Value>>,

    /// Cache of emitted const globals (value -> global)
    pub const_globals: RefCell<FxHashMap<&'ll Value, &'ll Value>>,

    /// List of globals for static variables which need to be passed to the
    /// LLVM function ReplaceAllUsesWith (RAUW) when codegen is complete.
    /// (We have to make sure we don't invalidate any Values referring
    /// to constants.)
    pub statics_to_rauw: RefCell<Vec<(&'ll Value, &'ll Value)>>,

    /// Statics that will be placed in the llvm.used variable
    /// See <https://llvm.org/docs/LangRef.html#the-llvm-used-global-variable> for details
    pub used_statics: RefCell<Vec<&'ll Value>>,

    /// Statics that will be placed in the llvm.compiler.used variable
    /// See <https://llvm.org/docs/LangRef.html#the-llvm-compiler-used-global-variable> for details
    pub compiler_used_statics: RefCell<Vec<&'ll Value>>,

    /// Mapping of non-scalar types to llvm types and field remapping if needed.
    pub type_lowering: RefCell<FxHashMap<(Ty<'tcx>, Option<VariantIdx>), TypeLowering<'ll>>>,

    /// Mapping of scalar types to llvm types.
    pub scalar_lltypes: RefCell<FxHashMap<Ty<'tcx>, &'ll Type>>,

    pub pointee_infos: RefCell<FxHashMap<(Ty<'tcx>, Size), Option<PointeeInfo>>>,
    pub isize_ty: &'ll Type,

    pub coverage_cx: Option<coverageinfo::CrateCoverageContext<'ll, 'tcx>>,
    pub dbg_cx: Option<debuginfo::CodegenUnitDebugContext<'ll, 'tcx>>,

    eh_personality: Cell<Option<&'ll Value>>,
    eh_catch_typeinfo: Cell<Option<&'ll Value>>,
    pub rust_try_fn: Cell<Option<(&'ll Type, &'ll Value)>>,

    intrinsics: RefCell<FxHashMap<&'static str, (&'ll Type, &'ll Value)>>,

    /// A counter that is used for generating local symbol names
    local_gen_sym_counter: Cell<usize>,

    /// `codegen_static` will sometimes create a second global variable with a
    /// different type and clear the symbol name of the original global.
    /// `global_asm!` needs to be able to find this new global so that it can
    /// compute the correct mangled symbol name to insert into the asm.
    pub renamed_statics: RefCell<FxHashMap<DefId, &'ll Value>>,
}

pub struct TypeLowering<'ll> {
    /// Associated LLVM type
    pub lltype: &'ll Type,

    /// If padding is used the slice maps fields from source order
    /// to llvm order.
    pub field_remapping: Option<SmallVec<[u32; 4]>>,
}

fn to_llvm_tls_model(tls_model: TlsModel) -> llvm::ThreadLocalMode {
    match tls_model {
        TlsModel::GeneralDynamic => llvm::ThreadLocalMode::GeneralDynamic,
        TlsModel::LocalDynamic => llvm::ThreadLocalMode::LocalDynamic,
        TlsModel::InitialExec => llvm::ThreadLocalMode::InitialExec,
        TlsModel::LocalExec => llvm::ThreadLocalMode::LocalExec,
    }
}

pub unsafe fn create_module<'ll>(
    tcx: TyCtxt<'_>,
    llcx: &'ll llvm::Context,
    mod_name: &str,
) -> &'ll llvm::Module {
    let sess = tcx.sess;
    let mod_name = SmallCStr::new(mod_name);
    let llmod = llvm::LLVMModuleCreateWithNameInContext(mod_name.as_ptr(), llcx);

    let mut target_data_layout = sess.target.data_layout.to_string();
    let llvm_version = llvm_util::get_version();
    if llvm_version < (16, 0, 0) {
        if sess.target.arch == "s390x" {
            // LLVM 16 data layout changed to always set 64-bit vector alignment,
            // which is conditional in earlier LLVM versions.
            // https://reviews.llvm.org/D131158 for the discussion.
            target_data_layout = target_data_layout.replace("-v128:64", "");
        } else if sess.target.arch == "riscv64" {
            // LLVM 16 introduced this change so as to produce more efficient code.
            // See https://reviews.llvm.org/D116735 for the discussion.
            target_data_layout = target_data_layout.replace("-n32:64-", "-n64-");
        }
    }

    // Ensure the data-layout values hardcoded remain the defaults.
    if sess.target.is_builtin {
        let tm = crate::back::write::create_informational_target_machine(tcx.sess);
        llvm::LLVMRustSetDataLayoutFromTargetMachine(llmod, tm);
        llvm::LLVMRustDisposeTargetMachine(tm);

        let llvm_data_layout = llvm::LLVMGetDataLayoutStr(llmod);
        let llvm_data_layout = str::from_utf8(CStr::from_ptr(llvm_data_layout).to_bytes())
            .expect("got a non-UTF8 data-layout from LLVM");

        // Unfortunately LLVM target specs change over time, and right now we
        // don't have proper support to work with any more than one
        // `data_layout` than the one that is in the rust-lang/rust repo. If
        // this compiler is configured against a custom LLVM, we may have a
        // differing data layout, even though we should update our own to use
        // that one.
        //
        // As an interim hack, if CFG_LLVM_ROOT is not an empty string then we
        // disable this check entirely as we may be configured with something
        // that has a different target layout.
        //
        // Unsure if this will actually cause breakage when rustc is configured
        // as such.
        //
        // FIXME(#34960)
        let cfg_llvm_root = option_env!("CFG_LLVM_ROOT").unwrap_or("");
        let custom_llvm_used = !cfg_llvm_root.trim().is_empty();

        if !custom_llvm_used && target_data_layout != llvm_data_layout {
            bug!(
                "data-layout for target `{rustc_target}`, `{rustc_layout}`, \
                  differs from LLVM target's `{llvm_target}` default layout, `{llvm_layout}`",
                rustc_target = sess.opts.target_triple,
                rustc_layout = target_data_layout,
                llvm_target = sess.target.llvm_target,
                llvm_layout = llvm_data_layout
            );
        }
    }

    let data_layout = SmallCStr::new(&target_data_layout);
    llvm::LLVMSetDataLayout(llmod, data_layout.as_ptr());

    let llvm_target = SmallCStr::new(&sess.target.llvm_target);
    llvm::LLVMRustSetNormalizedTarget(llmod, llvm_target.as_ptr());

    let reloc_model = sess.relocation_model();
    if matches!(reloc_model, RelocModel::Pic | RelocModel::Pie) {
        llvm::LLVMRustSetModulePICLevel(llmod);
        // PIE is potentially more effective than PIC, but can only be used in executables.
        // If all our outputs are executables, then we can relax PIC to PIE.
        if reloc_model == RelocModel::Pie
            || sess.crate_types().iter().all(|ty| *ty == CrateType::Executable)
        {
            llvm::LLVMRustSetModulePIELevel(llmod);
        }
    }

    // Linking object files with different code models is undefined behavior
    // because the compiler would have to generate additional code (to span
    // longer jumps) if a larger code model is used with a smaller one.
    //
    // See https://reviews.llvm.org/D52322 and https://reviews.llvm.org/D52323.
    llvm::LLVMRustSetModuleCodeModel(llmod, to_llvm_code_model(sess.code_model()));

    // If skipping the PLT is enabled, we need to add some module metadata
    // to ensure intrinsic calls don't use it.
    if !sess.needs_plt() {
        let avoid_plt = "RtLibUseGOT\0".as_ptr().cast();
        llvm::LLVMRustAddModuleFlag(llmod, llvm::LLVMModFlagBehavior::Warning, avoid_plt, 1);
    }

    // Enable canonical jump tables if CFI is enabled. (See https://reviews.llvm.org/D65629.)
    if sess.is_sanitizer_cfi_canonical_jump_tables_enabled() && sess.is_sanitizer_cfi_enabled() {
        let canonical_jump_tables = "CFI Canonical Jump Tables\0".as_ptr().cast();
        llvm::LLVMRustAddModuleFlag(
            llmod,
            llvm::LLVMModFlagBehavior::Override,
            canonical_jump_tables,
            1,
        );
    }

    // Enable LTO unit splitting if specified or if CFI is enabled. (See https://reviews.llvm.org/D53891.)
    if sess.is_split_lto_unit_enabled() || sess.is_sanitizer_cfi_enabled() {
        let enable_split_lto_unit = "EnableSplitLTOUnit\0".as_ptr().cast();
        llvm::LLVMRustAddModuleFlag(
            llmod,
            llvm::LLVMModFlagBehavior::Override,
            enable_split_lto_unit,
            1,
        );
    }

    // Add "kcfi" module flag if KCFI is enabled. (See https://reviews.llvm.org/D119296.)
    if sess.is_sanitizer_kcfi_enabled() {
        let kcfi = "kcfi\0".as_ptr().cast();
        llvm::LLVMRustAddModuleFlag(llmod, llvm::LLVMModFlagBehavior::Override, kcfi, 1);
    }

    // Control Flow Guard is currently only supported by the MSVC linker on Windows.
    if sess.target.is_like_msvc {
        match sess.opts.cg.control_flow_guard {
            CFGuard::Disabled => {}
            CFGuard::NoChecks => {
                // Set `cfguard=1` module flag to emit metadata only.
                llvm::LLVMRustAddModuleFlag(
                    llmod,
                    llvm::LLVMModFlagBehavior::Warning,
                    "cfguard\0".as_ptr() as *const _,
                    1,
                )
            }
            CFGuard::Checks => {
                // Set `cfguard=2` module flag to emit metadata and checks.
                llvm::LLVMRustAddModuleFlag(
                    llmod,
                    llvm::LLVMModFlagBehavior::Warning,
                    "cfguard\0".as_ptr() as *const _,
                    2,
                )
            }
        }
    }

    if let Some(BranchProtection { bti, pac_ret }) = sess.opts.unstable_opts.branch_protection {
        let behavior = if llvm_version >= (15, 0, 0) {
            llvm::LLVMModFlagBehavior::Min
        } else {
            llvm::LLVMModFlagBehavior::Error
        };

        if sess.target.arch == "aarch64" {
            llvm::LLVMRustAddModuleFlag(
                llmod,
                behavior,
                "branch-target-enforcement\0".as_ptr().cast(),
                bti.into(),
            );
            llvm::LLVMRustAddModuleFlag(
                llmod,
                behavior,
                "sign-return-address\0".as_ptr().cast(),
                pac_ret.is_some().into(),
            );
            let pac_opts = pac_ret.unwrap_or(PacRet { leaf: false, key: PAuthKey::A });
            llvm::LLVMRustAddModuleFlag(
                llmod,
                behavior,
                "sign-return-address-all\0".as_ptr().cast(),
                pac_opts.leaf.into(),
            );
            llvm::LLVMRustAddModuleFlag(
                llmod,
                behavior,
                "sign-return-address-with-bkey\0".as_ptr().cast(),
                u32::from(pac_opts.key == PAuthKey::B),
            );
        } else {
            bug!(
                "branch-protection used on non-AArch64 target; \
                  this should be checked in rustc_session."
            );
        }
    }

    // Pass on the control-flow protection flags to LLVM (equivalent to `-fcf-protection` in Clang).
    if let CFProtection::Branch | CFProtection::Full = sess.opts.unstable_opts.cf_protection {
        llvm::LLVMRustAddModuleFlag(
            llmod,
            llvm::LLVMModFlagBehavior::Override,
            "cf-protection-branch\0".as_ptr().cast(),
            1,
        )
    }
    if let CFProtection::Return | CFProtection::Full = sess.opts.unstable_opts.cf_protection {
        llvm::LLVMRustAddModuleFlag(
            llmod,
            llvm::LLVMModFlagBehavior::Override,
            "cf-protection-return\0".as_ptr().cast(),
            1,
        )
    }

    if sess.opts.unstable_opts.virtual_function_elimination {
        llvm::LLVMRustAddModuleFlag(
            llmod,
            llvm::LLVMModFlagBehavior::Error,
            "Virtual Function Elim\0".as_ptr().cast(),
            1,
        );
    }

    llmod
}

impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
    pub(crate) fn new(
        tcx: TyCtxt<'tcx>,
        codegen_unit: &'tcx CodegenUnit<'tcx>,
        llvm_module: &'ll crate::ModuleLlvm,
    ) -> Self {
        // An interesting part of Windows which MSVC forces our hand on (and
        // apparently MinGW didn't) is the usage of `dllimport` and `dllexport`
        // attributes in LLVM IR as well as native dependencies (in C these
        // correspond to `__declspec(dllimport)`).
        //
        // LD (BFD) in MinGW mode can often correctly guess `dllexport` but
        // relying on that can result in issues like #50176.
        // LLD won't support that and expects symbols with proper attributes.
        // Because of that we make MinGW target emit dllexport just like MSVC.
        // When it comes to dllimport we use it for constants but for functions
        // rely on the linker to do the right thing. Opposed to dllexport this
        // task is easy for them (both LD and LLD) and allows us to easily use
        // symbols from static libraries in shared libraries.
        //
        // Whenever a dynamic library is built on Windows it must have its public
        // interface specified by functions tagged with `dllexport` or otherwise
        // they're not available to be linked against. This poses a few problems
        // for the compiler, some of which are somewhat fundamental, but we use
        // the `use_dll_storage_attrs` variable below to attach the `dllexport`
        // attribute to all LLVM functions that are exported e.g., they're
        // already tagged with external linkage). This is suboptimal for a few
        // reasons:
        //
        // * If an object file will never be included in a dynamic library,
        //   there's no need to attach the dllexport attribute. Most object
        //   files in Rust are not destined to become part of a dll as binaries
        //   are statically linked by default.
        // * If the compiler is emitting both an rlib and a dylib, the same
        //   source object file is currently used but with MSVC this may be less
        //   feasible. The compiler may be able to get around this, but it may
        //   involve some invasive changes to deal with this.
        //
        // The flip side of this situation is that whenever you link to a dll and
        // you import a function from it, the import should be tagged with
        // `dllimport`. At this time, however, the compiler does not emit
        // `dllimport` for any declarations other than constants (where it is
        // required), which is again suboptimal for even more reasons!
        //
        // * Calling a function imported from another dll without using
        //   `dllimport` causes the linker/compiler to have extra overhead (one
        //   `jmp` instruction on x86) when calling the function.
        // * The same object file may be used in different circumstances, so a
        //   function may be imported from a dll if the object is linked into a
        //   dll, but it may be just linked against if linked into an rlib.
        // * The compiler has no knowledge about whether native functions should
        //   be tagged dllimport or not.
        //
        // For now the compiler takes the perf hit (I do not have any numbers to
        // this effect) by marking very little as `dllimport` and praying the
        // linker will take care of everything. Fixing this problem will likely
        // require adding a few attributes to Rust itself (feature gated at the
        // start) and then strongly recommending static linkage on Windows!
        let use_dll_storage_attrs = tcx.sess.target.is_like_windows;

        let check_overflow = tcx.sess.overflow_checks();

        let tls_model = to_llvm_tls_model(tcx.sess.tls_model());

        let (llcx, llmod) = (&*llvm_module.llcx, llvm_module.llmod());

        let coverage_cx =
            tcx.sess.instrument_coverage().then(coverageinfo::CrateCoverageContext::new);

        let dbg_cx = if tcx.sess.opts.debuginfo != DebugInfo::None {
            let dctx = debuginfo::CodegenUnitDebugContext::new(llmod);
            debuginfo::metadata::build_compile_unit_di_node(
                tcx,
                codegen_unit.name().as_str(),
                &dctx,
            );
            Some(dctx)
        } else {
            None
        };

        let isize_ty = Type::ix_llcx(llcx, tcx.data_layout.pointer_size.bits());

        CodegenCx {
            tcx,
            check_overflow,
            use_dll_storage_attrs,
            tls_model,
            llmod,
            llcx,
            codegen_unit,
            instances: Default::default(),
            vtables: Default::default(),
            const_str_cache: Default::default(),
            const_unsized: Default::default(),
            const_globals: Default::default(),
            statics_to_rauw: RefCell::new(Vec::new()),
            used_statics: RefCell::new(Vec::new()),
            compiler_used_statics: RefCell::new(Vec::new()),
            type_lowering: Default::default(),
            scalar_lltypes: Default::default(),
            pointee_infos: Default::default(),
            isize_ty,
            coverage_cx,
            dbg_cx,
            eh_personality: Cell::new(None),
            eh_catch_typeinfo: Cell::new(None),
            rust_try_fn: Cell::new(None),
            intrinsics: Default::default(),
            local_gen_sym_counter: Cell::new(0),
            renamed_statics: Default::default(),
        }
    }

    pub(crate) fn statics_to_rauw(&self) -> &RefCell<Vec<(&'ll Value, &'ll Value)>> {
        &self.statics_to_rauw
    }

    #[inline]
    pub fn coverage_context(&self) -> Option<&coverageinfo::CrateCoverageContext<'ll, 'tcx>> {
        self.coverage_cx.as_ref()
    }

    pub(crate) fn create_used_variable_impl(&self, name: &'static CStr, values: &[&'ll Value]) {
        let section = cstr!("llvm.metadata");
        let array = self.const_array(self.type_ptr_to(self.type_i8()), values);

        unsafe {
            let g = llvm::LLVMAddGlobal(self.llmod, self.val_ty(array), name.as_ptr());
            llvm::LLVMSetInitializer(g, array);
            llvm::LLVMRustSetLinkage(g, llvm::Linkage::AppendingLinkage);
            llvm::LLVMSetSection(g, section.as_ptr());
        }
    }
}

impl<'ll, 'tcx> MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
    fn vtables(
        &self,
    ) -> &RefCell<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), &'ll Value>>
    {
        &self.vtables
    }

    fn get_fn(&self, instance: Instance<'tcx>) -> &'ll Value {
        get_fn(self, instance)
    }

    fn get_fn_addr(&self, instance: Instance<'tcx>) -> &'ll Value {
        get_fn(self, instance)
    }

    fn eh_personality(&self) -> &'ll Value {
        // The exception handling personality function.
        //
        // If our compilation unit has the `eh_personality` lang item somewhere
        // within it, then we just need to codegen that. Otherwise, we're
        // building an rlib which will depend on some upstream implementation of
        // this function, so we just codegen a generic reference to it. We don't
        // specify any of the types for the function, we just make it a symbol
        // that LLVM can later use.
        //
        // Note that MSVC is a little special here in that we don't use the
        // `eh_personality` lang item at all. Currently LLVM has support for
        // both Dwarf and SEH unwind mechanisms for MSVC targets and uses the
        // *name of the personality function* to decide what kind of unwind side
        // tables/landing pads to emit. It looks like Dwarf is used by default,
        // injecting a dependency on the `_Unwind_Resume` symbol for resuming
        // an "exception", but for MSVC we want to force SEH. This means that we
        // can't actually have the personality function be our standard
        // `rust_eh_personality` function, but rather we wired it up to the
        // CRT's custom personality function, which forces LLVM to consider
        // landing pads as "landing pads for SEH".
        if let Some(llpersonality) = self.eh_personality.get() {
            return llpersonality;
        }

        let name = if wants_msvc_seh(self.sess()) {
            Some("__CxxFrameHandler3")
        } else if wants_wasm_eh(self.sess()) {
            // LLVM specifically tests for the name of the personality function
            // There is no need for this function to exist anywhere, it will
            // not be called. However, its name has to be "__gxx_wasm_personality_v0"
            // for native wasm exceptions.
            Some("__gxx_wasm_personality_v0")
        } else {
            None
        };

        let tcx = self.tcx;
        let llfn = match tcx.lang_items().eh_personality() {
            Some(def_id) if name.is_none() => self.get_fn_addr(
                ty::Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, ty::List::empty())
                    .unwrap()
                    .unwrap(),
            ),
            _ => {
                let name = name.unwrap_or("rust_eh_personality");
                if let Some(llfn) = self.get_declared_value(name) {
                    llfn
                } else {
                    let fty = self.type_variadic_func(&[], self.type_i32());
                    let llfn = self.declare_cfn(name, llvm::UnnamedAddr::Global, fty);
                    let target_cpu = attributes::target_cpu_attr(self);
                    attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[target_cpu]);
                    llfn
                }
            }
        };
        self.eh_personality.set(Some(llfn));
        llfn
    }

    fn sess(&self) -> &Session {
        self.tcx.sess
    }

    fn check_overflow(&self) -> bool {
        self.check_overflow
    }

    fn codegen_unit(&self) -> &'tcx CodegenUnit<'tcx> {
        self.codegen_unit
    }

    fn set_frame_pointer_type(&self, llfn: &'ll Value) {
        if let Some(attr) = attributes::frame_pointer_type_attr(self) {
            attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[attr]);
        }
    }

    fn apply_target_cpu_attr(&self, llfn: &'ll Value) {
        let mut attrs = SmallVec::<[_; 2]>::new();
        attrs.push(attributes::target_cpu_attr(self));
        attrs.extend(attributes::tune_cpu_attr(self));
        attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &attrs);
    }

    fn declare_c_main(&self, fn_type: Self::Type) -> Option<Self::Function> {
        let entry_name = self.sess().target.entry_name.as_ref();
        if self.get_declared_value(entry_name).is_none() {
            Some(self.declare_entry_fn(
                entry_name,
                self.sess().target.entry_abi.into(),
                llvm::UnnamedAddr::Global,
                fn_type,
            ))
        } else {
            // If the symbol already exists, it is an error: for example, the user wrote
            // #[no_mangle] extern "C" fn main(..) {..}
            // instead of #[start]
            None
        }
    }
}

impl<'ll> CodegenCx<'ll, '_> {
    pub(crate) fn get_intrinsic(&self, key: &str) -> (&'ll Type, &'ll Value) {
        if let Some(v) = self.intrinsics.borrow().get(key).cloned() {
            return v;
        }

        self.declare_intrinsic(key).unwrap_or_else(|| bug!("unknown intrinsic '{}'", key))
    }

    fn insert_intrinsic(
        &self,
        name: &'static str,
        args: Option<&[&'ll llvm::Type]>,
        ret: &'ll llvm::Type,
    ) -> (&'ll llvm::Type, &'ll llvm::Value) {
        let fn_ty = if let Some(args) = args {
            self.type_func(args, ret)
        } else {
            self.type_variadic_func(&[], ret)
        };
        let f = self.declare_cfn(name, llvm::UnnamedAddr::No, fn_ty);
        self.intrinsics.borrow_mut().insert(name, (fn_ty, f));
        (fn_ty, f)
    }

    fn declare_intrinsic(&self, key: &str) -> Option<(&'ll Type, &'ll Value)> {
        macro_rules! ifn {
            ($name:expr, fn() -> $ret:expr) => (
                if key == $name {
                    return Some(self.insert_intrinsic($name, Some(&[]), $ret));
                }
            );
            ($name:expr, fn(...) -> $ret:expr) => (
                if key == $name {
                    return Some(self.insert_intrinsic($name, None, $ret));
                }
            );
            ($name:expr, fn($($arg:expr),*) -> $ret:expr) => (
                if key == $name {
                    return Some(self.insert_intrinsic($name, Some(&[$($arg),*]), $ret));
                }
            );
        }
        macro_rules! mk_struct {
            ($($field_ty:expr),*) => (self.type_struct( &[$($field_ty),*], false))
        }

        let i8p = self.type_i8p();
        let void = self.type_void();
        let i1 = self.type_i1();
        let t_i8 = self.type_i8();
        let t_i16 = self.type_i16();
        let t_i32 = self.type_i32();
        let t_i64 = self.type_i64();
        let t_i128 = self.type_i128();
        let t_isize = self.type_isize();
        let t_f32 = self.type_f32();
        let t_f64 = self.type_f64();
        let t_metadata = self.type_metadata();
        let t_token = self.type_token();

        ifn!("llvm.wasm.get.exception", fn(t_token) -> i8p);
        ifn!("llvm.wasm.get.ehselector", fn(t_token) -> t_i32);

        ifn!("llvm.wasm.trunc.unsigned.i32.f32", fn(t_f32) -> t_i32);
        ifn!("llvm.wasm.trunc.unsigned.i32.f64", fn(t_f64) -> t_i32);
        ifn!("llvm.wasm.trunc.unsigned.i64.f32", fn(t_f32) -> t_i64);
        ifn!("llvm.wasm.trunc.unsigned.i64.f64", fn(t_f64) -> t_i64);
        ifn!("llvm.wasm.trunc.signed.i32.f32", fn(t_f32) -> t_i32);
        ifn!("llvm.wasm.trunc.signed.i32.f64", fn(t_f64) -> t_i32);
        ifn!("llvm.wasm.trunc.signed.i64.f32", fn(t_f32) -> t_i64);
        ifn!("llvm.wasm.trunc.signed.i64.f64", fn(t_f64) -> t_i64);

        ifn!("llvm.fptosi.sat.i8.f32", fn(t_f32) -> t_i8);
        ifn!("llvm.fptosi.sat.i16.f32", fn(t_f32) -> t_i16);
        ifn!("llvm.fptosi.sat.i32.f32", fn(t_f32) -> t_i32);
        ifn!("llvm.fptosi.sat.i64.f32", fn(t_f32) -> t_i64);
        ifn!("llvm.fptosi.sat.i128.f32", fn(t_f32) -> t_i128);
        ifn!("llvm.fptosi.sat.i8.f64", fn(t_f64) -> t_i8);
        ifn!("llvm.fptosi.sat.i16.f64", fn(t_f64) -> t_i16);
        ifn!("llvm.fptosi.sat.i32.f64", fn(t_f64) -> t_i32);
        ifn!("llvm.fptosi.sat.i64.f64", fn(t_f64) -> t_i64);
        ifn!("llvm.fptosi.sat.i128.f64", fn(t_f64) -> t_i128);

        ifn!("llvm.fptoui.sat.i8.f32", fn(t_f32) -> t_i8);
        ifn!("llvm.fptoui.sat.i16.f32", fn(t_f32) -> t_i16);
        ifn!("llvm.fptoui.sat.i32.f32", fn(t_f32) -> t_i32);
        ifn!("llvm.fptoui.sat.i64.f32", fn(t_f32) -> t_i64);
        ifn!("llvm.fptoui.sat.i128.f32", fn(t_f32) -> t_i128);
        ifn!("llvm.fptoui.sat.i8.f64", fn(t_f64) -> t_i8);
        ifn!("llvm.fptoui.sat.i16.f64", fn(t_f64) -> t_i16);
        ifn!("llvm.fptoui.sat.i32.f64", fn(t_f64) -> t_i32);
        ifn!("llvm.fptoui.sat.i64.f64", fn(t_f64) -> t_i64);
        ifn!("llvm.fptoui.sat.i128.f64", fn(t_f64) -> t_i128);

        ifn!("llvm.trap", fn() -> void);
        ifn!("llvm.debugtrap", fn() -> void);
        ifn!("llvm.frameaddress", fn(t_i32) -> i8p);

        ifn!("llvm.powi.f32", fn(t_f32, t_i32) -> t_f32);
        ifn!("llvm.powi.f64", fn(t_f64, t_i32) -> t_f64);

        ifn!("llvm.pow.f32", fn(t_f32, t_f32) -> t_f32);
        ifn!("llvm.pow.f64", fn(t_f64, t_f64) -> t_f64);

        ifn!("llvm.sqrt.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.sqrt.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.sin.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.sin.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.cos.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.cos.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.exp.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.exp.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.exp2.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.exp2.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.log.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.log.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.log10.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.log10.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.log2.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.log2.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.fma.f32", fn(t_f32, t_f32, t_f32) -> t_f32);
        ifn!("llvm.fma.f64", fn(t_f64, t_f64, t_f64) -> t_f64);

        ifn!("llvm.fabs.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.fabs.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.minnum.f32", fn(t_f32, t_f32) -> t_f32);
        ifn!("llvm.minnum.f64", fn(t_f64, t_f64) -> t_f64);
        ifn!("llvm.maxnum.f32", fn(t_f32, t_f32) -> t_f32);
        ifn!("llvm.maxnum.f64", fn(t_f64, t_f64) -> t_f64);

        ifn!("llvm.floor.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.floor.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.ceil.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.ceil.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.trunc.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.trunc.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.copysign.f32", fn(t_f32, t_f32) -> t_f32);
        ifn!("llvm.copysign.f64", fn(t_f64, t_f64) -> t_f64);

        ifn!("llvm.round.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.round.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.roundeven.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.roundeven.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.rint.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.rint.f64", fn(t_f64) -> t_f64);
        ifn!("llvm.nearbyint.f32", fn(t_f32) -> t_f32);
        ifn!("llvm.nearbyint.f64", fn(t_f64) -> t_f64);

        ifn!("llvm.ctpop.i8", fn(t_i8) -> t_i8);
        ifn!("llvm.ctpop.i16", fn(t_i16) -> t_i16);
        ifn!("llvm.ctpop.i32", fn(t_i32) -> t_i32);
        ifn!("llvm.ctpop.i64", fn(t_i64) -> t_i64);
        ifn!("llvm.ctpop.i128", fn(t_i128) -> t_i128);

        ifn!("llvm.ctlz.i8", fn(t_i8, i1) -> t_i8);
        ifn!("llvm.ctlz.i16", fn(t_i16, i1) -> t_i16);
        ifn!("llvm.ctlz.i32", fn(t_i32, i1) -> t_i32);
        ifn!("llvm.ctlz.i64", fn(t_i64, i1) -> t_i64);
        ifn!("llvm.ctlz.i128", fn(t_i128, i1) -> t_i128);

        ifn!("llvm.cttz.i8", fn(t_i8, i1) -> t_i8);
        ifn!("llvm.cttz.i16", fn(t_i16, i1) -> t_i16);
        ifn!("llvm.cttz.i32", fn(t_i32, i1) -> t_i32);
        ifn!("llvm.cttz.i64", fn(t_i64, i1) -> t_i64);
        ifn!("llvm.cttz.i128", fn(t_i128, i1) -> t_i128);

        ifn!("llvm.bswap.i16", fn(t_i16) -> t_i16);
        ifn!("llvm.bswap.i32", fn(t_i32) -> t_i32);
        ifn!("llvm.bswap.i64", fn(t_i64) -> t_i64);
        ifn!("llvm.bswap.i128", fn(t_i128) -> t_i128);

        ifn!("llvm.bitreverse.i8", fn(t_i8) -> t_i8);
        ifn!("llvm.bitreverse.i16", fn(t_i16) -> t_i16);
        ifn!("llvm.bitreverse.i32", fn(t_i32) -> t_i32);
        ifn!("llvm.bitreverse.i64", fn(t_i64) -> t_i64);
        ifn!("llvm.bitreverse.i128", fn(t_i128) -> t_i128);

        ifn!("llvm.fshl.i8", fn(t_i8, t_i8, t_i8) -> t_i8);
        ifn!("llvm.fshl.i16", fn(t_i16, t_i16, t_i16) -> t_i16);
        ifn!("llvm.fshl.i32", fn(t_i32, t_i32, t_i32) -> t_i32);
        ifn!("llvm.fshl.i64", fn(t_i64, t_i64, t_i64) -> t_i64);
        ifn!("llvm.fshl.i128", fn(t_i128, t_i128, t_i128) -> t_i128);

        ifn!("llvm.fshr.i8", fn(t_i8, t_i8, t_i8) -> t_i8);
        ifn!("llvm.fshr.i16", fn(t_i16, t_i16, t_i16) -> t_i16);
        ifn!("llvm.fshr.i32", fn(t_i32, t_i32, t_i32) -> t_i32);
        ifn!("llvm.fshr.i64", fn(t_i64, t_i64, t_i64) -> t_i64);
        ifn!("llvm.fshr.i128", fn(t_i128, t_i128, t_i128) -> t_i128);

        ifn!("llvm.sadd.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct! {t_i8, i1});
        ifn!("llvm.sadd.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct! {t_i16, i1});
        ifn!("llvm.sadd.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct! {t_i32, i1});
        ifn!("llvm.sadd.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct! {t_i64, i1});
        ifn!("llvm.sadd.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct! {t_i128, i1});

        ifn!("llvm.uadd.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct! {t_i8, i1});
        ifn!("llvm.uadd.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct! {t_i16, i1});
        ifn!("llvm.uadd.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct! {t_i32, i1});
        ifn!("llvm.uadd.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct! {t_i64, i1});
        ifn!("llvm.uadd.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct! {t_i128, i1});

        ifn!("llvm.ssub.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct! {t_i8, i1});
        ifn!("llvm.ssub.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct! {t_i16, i1});
        ifn!("llvm.ssub.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct! {t_i32, i1});
        ifn!("llvm.ssub.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct! {t_i64, i1});
        ifn!("llvm.ssub.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct! {t_i128, i1});

        ifn!("llvm.usub.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct! {t_i8, i1});
        ifn!("llvm.usub.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct! {t_i16, i1});
        ifn!("llvm.usub.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct! {t_i32, i1});
        ifn!("llvm.usub.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct! {t_i64, i1});
        ifn!("llvm.usub.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct! {t_i128, i1});

        ifn!("llvm.smul.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct! {t_i8, i1});
        ifn!("llvm.smul.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct! {t_i16, i1});
        ifn!("llvm.smul.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct! {t_i32, i1});
        ifn!("llvm.smul.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct! {t_i64, i1});
        ifn!("llvm.smul.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct! {t_i128, i1});

        ifn!("llvm.umul.with.overflow.i8", fn(t_i8, t_i8) -> mk_struct! {t_i8, i1});
        ifn!("llvm.umul.with.overflow.i16", fn(t_i16, t_i16) -> mk_struct! {t_i16, i1});
        ifn!("llvm.umul.with.overflow.i32", fn(t_i32, t_i32) -> mk_struct! {t_i32, i1});
        ifn!("llvm.umul.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct! {t_i64, i1});
        ifn!("llvm.umul.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct! {t_i128, i1});

        ifn!("llvm.sadd.sat.i8", fn(t_i8, t_i8) -> t_i8);
        ifn!("llvm.sadd.sat.i16", fn(t_i16, t_i16) -> t_i16);
        ifn!("llvm.sadd.sat.i32", fn(t_i32, t_i32) -> t_i32);
        ifn!("llvm.sadd.sat.i64", fn(t_i64, t_i64) -> t_i64);
        ifn!("llvm.sadd.sat.i128", fn(t_i128, t_i128) -> t_i128);

        ifn!("llvm.uadd.sat.i8", fn(t_i8, t_i8) -> t_i8);
        ifn!("llvm.uadd.sat.i16", fn(t_i16, t_i16) -> t_i16);
        ifn!("llvm.uadd.sat.i32", fn(t_i32, t_i32) -> t_i32);
        ifn!("llvm.uadd.sat.i64", fn(t_i64, t_i64) -> t_i64);
        ifn!("llvm.uadd.sat.i128", fn(t_i128, t_i128) -> t_i128);

        ifn!("llvm.ssub.sat.i8", fn(t_i8, t_i8) -> t_i8);
        ifn!("llvm.ssub.sat.i16", fn(t_i16, t_i16) -> t_i16);
        ifn!("llvm.ssub.sat.i32", fn(t_i32, t_i32) -> t_i32);
        ifn!("llvm.ssub.sat.i64", fn(t_i64, t_i64) -> t_i64);
        ifn!("llvm.ssub.sat.i128", fn(t_i128, t_i128) -> t_i128);

        ifn!("llvm.usub.sat.i8", fn(t_i8, t_i8) -> t_i8);
        ifn!("llvm.usub.sat.i16", fn(t_i16, t_i16) -> t_i16);
        ifn!("llvm.usub.sat.i32", fn(t_i32, t_i32) -> t_i32);
        ifn!("llvm.usub.sat.i64", fn(t_i64, t_i64) -> t_i64);
        ifn!("llvm.usub.sat.i128", fn(t_i128, t_i128) -> t_i128);

        ifn!("llvm.lifetime.start.p0i8", fn(t_i64, i8p) -> void);
        ifn!("llvm.lifetime.end.p0i8", fn(t_i64, i8p) -> void);

        ifn!("llvm.expect.i1", fn(i1, i1) -> i1);
        ifn!("llvm.eh.typeid.for", fn(i8p) -> t_i32);
        ifn!("llvm.localescape", fn(...) -> void);
        ifn!("llvm.localrecover", fn(i8p, i8p, t_i32) -> i8p);
        ifn!("llvm.x86.seh.recoverfp", fn(i8p, i8p) -> i8p);

        ifn!("llvm.assume", fn(i1) -> void);
        ifn!("llvm.prefetch", fn(i8p, t_i32, t_i32, t_i32) -> void);

        // This isn't an "LLVM intrinsic", but LLVM's optimization passes
        // recognize it like one and we assume it exists in `core::slice::cmp`
        match self.sess().target.arch.as_ref() {
            "avr" | "msp430" => ifn!("memcmp", fn(i8p, i8p, t_isize) -> t_i16),
            _ => ifn!("memcmp", fn(i8p, i8p, t_isize) -> t_i32),
        }

        // variadic intrinsics
        ifn!("llvm.va_start", fn(i8p) -> void);
        ifn!("llvm.va_end", fn(i8p) -> void);
        ifn!("llvm.va_copy", fn(i8p, i8p) -> void);

        if self.sess().instrument_coverage() {
            ifn!("llvm.instrprof.increment", fn(i8p, t_i64, t_i32, t_i32) -> void);
        }

        ifn!("llvm.type.test", fn(i8p, t_metadata) -> i1);
        ifn!("llvm.type.checked.load", fn(i8p, t_i32, t_metadata) -> mk_struct! {i8p, i1});

        if self.sess().opts.debuginfo != DebugInfo::None {
            ifn!("llvm.dbg.declare", fn(t_metadata, t_metadata) -> void);
            ifn!("llvm.dbg.value", fn(t_metadata, t_i64, t_metadata) -> void);
        }

        ifn!("llvm.ptrmask", fn(i8p, t_isize) -> i8p);

        None
    }

    pub(crate) fn eh_catch_typeinfo(&self) -> &'ll Value {
        if let Some(eh_catch_typeinfo) = self.eh_catch_typeinfo.get() {
            return eh_catch_typeinfo;
        }
        let tcx = self.tcx;
        assert!(self.sess().target.os == "emscripten");
        let eh_catch_typeinfo = match tcx.lang_items().eh_catch_typeinfo() {
            Some(def_id) => self.get_static(def_id),
            _ => {
                let ty = self
                    .type_struct(&[self.type_ptr_to(self.type_isize()), self.type_i8p()], false);
                self.declare_global("rust_eh_catch_typeinfo", ty)
            }
        };
        let eh_catch_typeinfo = self.const_bitcast(eh_catch_typeinfo, self.type_i8p());
        self.eh_catch_typeinfo.set(Some(eh_catch_typeinfo));
        eh_catch_typeinfo
    }
}

impl CodegenCx<'_, '_> {
    /// Generates a new symbol name with the given prefix. This symbol name must
    /// only be used for definitions with `internal` or `private` linkage.
    pub fn generate_local_symbol_name(&self, prefix: &str) -> String {
        let idx = self.local_gen_sym_counter.get();
        self.local_gen_sym_counter.set(idx + 1);
        // Include a '.' character, so there can be no accidental conflicts with
        // user defined names
        let mut name = String::with_capacity(prefix.len() + 6);
        name.push_str(prefix);
        name.push('.');
        base_n::push_str(idx as u128, base_n::ALPHANUMERIC_ONLY, &mut name);
        name
    }
}

impl HasDataLayout for CodegenCx<'_, '_> {
    #[inline]
    fn data_layout(&self) -> &TargetDataLayout {
        &self.tcx.data_layout
    }
}

impl HasTargetSpec for CodegenCx<'_, '_> {
    #[inline]
    fn target_spec(&self) -> &Target {
        &self.tcx.sess.target
    }
}

impl<'tcx> ty::layout::HasTyCtxt<'tcx> for CodegenCx<'_, 'tcx> {
    #[inline]
    fn tcx(&self) -> TyCtxt<'tcx> {
        self.tcx
    }
}

impl<'tcx, 'll> HasParamEnv<'tcx> for CodegenCx<'ll, 'tcx> {
    fn param_env(&self) -> ty::ParamEnv<'tcx> {
        ty::ParamEnv::reveal_all()
    }
}

impl<'tcx> LayoutOfHelpers<'tcx> for CodegenCx<'_, 'tcx> {
    type LayoutOfResult = TyAndLayout<'tcx>;

    #[inline]
    fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
        if let LayoutError::SizeOverflow(_) = err {
            self.sess().emit_fatal(Spanned { span, node: err.into_diagnostic() })
        } else {
            span_bug!(span, "failed to get layout for `{ty}`: {err:?}")
        }
    }
}

impl<'tcx> FnAbiOfHelpers<'tcx> for CodegenCx<'_, 'tcx> {
    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;

    #[inline]
    fn handle_fn_abi_err(
        &self,
        err: FnAbiError<'tcx>,
        span: Span,
        fn_abi_request: FnAbiRequest<'tcx>,
    ) -> ! {
        if let FnAbiError::Layout(LayoutError::SizeOverflow(_)) = err {
            self.sess().emit_fatal(Spanned { span, node: err })
        } else {
            match fn_abi_request {
                FnAbiRequest::OfFnPtr { sig, extra_args } => {
                    span_bug!(span, "`fn_abi_of_fn_ptr({sig}, {extra_args:?})` failed: {err:?}",);
                }
                FnAbiRequest::OfInstance { instance, extra_args } => {
                    span_bug!(
                        span,
                        "`fn_abi_of_instance({instance}, {extra_args:?})` failed: {err:?}",
                    );
                }
            }
        }
    }
}