intrinsic.rs

use crate::abi::{Abi, FnAbi, FnAbiLlvmExt, LlvmType, PassMode};
use crate::builder::Builder;
use crate::context::CodegenCx;
use crate::llvm;
use crate::type_::Type;
use crate::type_of::LayoutLlvmExt;
use crate::va_arg::emit_va_arg;
use crate::value::Value;

use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh};
use rustc_codegen_ssa::common::span_invalid_monomorphization_error;
use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
use rustc_codegen_ssa::mir::operand::OperandRef;
use rustc_codegen_ssa::mir::place::PlaceRef;
use rustc_codegen_ssa::traits::*;
use rustc_hir as hir;
use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, LayoutOf};
use rustc_middle::ty::{self, Ty};
use rustc_middle::{bug, span_bug};
use rustc_span::{sym, symbol::kw, Span, Symbol};
use rustc_target::abi::{self, Align, HasDataLayout, Primitive};
use rustc_target::spec::{HasTargetSpec, PanicStrategy};

use std::cmp::Ordering;
use std::iter;

fn get_simple_intrinsic<'ll>(
    cx: &CodegenCx<'ll, '_>,
    name: Symbol,
) -> Option<(&'ll Type, &'ll Value)> {
    let llvm_name = match name {
        sym::sqrtf32 => "llvm.sqrt.f32",
        sym::sqrtf64 => "llvm.sqrt.f64",
        sym::powif32 => "llvm.powi.f32",
        sym::powif64 => "llvm.powi.f64",
        sym::sinf32 => "llvm.sin.f32",
        sym::sinf64 => "llvm.sin.f64",
        sym::cosf32 => "llvm.cos.f32",
        sym::cosf64 => "llvm.cos.f64",
        sym::powf32 => "llvm.pow.f32",
        sym::powf64 => "llvm.pow.f64",
        sym::expf32 => "llvm.exp.f32",
        sym::expf64 => "llvm.exp.f64",
        sym::exp2f32 => "llvm.exp2.f32",
        sym::exp2f64 => "llvm.exp2.f64",
        sym::logf32 => "llvm.log.f32",
        sym::logf64 => "llvm.log.f64",
        sym::log10f32 => "llvm.log10.f32",
        sym::log10f64 => "llvm.log10.f64",
        sym::log2f32 => "llvm.log2.f32",
        sym::log2f64 => "llvm.log2.f64",
        sym::fmaf32 => "llvm.fma.f32",
        sym::fmaf64 => "llvm.fma.f64",
        sym::fabsf32 => "llvm.fabs.f32",
        sym::fabsf64 => "llvm.fabs.f64",
        sym::minnumf32 => "llvm.minnum.f32",
        sym::minnumf64 => "llvm.minnum.f64",
        sym::maxnumf32 => "llvm.maxnum.f32",
        sym::maxnumf64 => "llvm.maxnum.f64",
        sym::copysignf32 => "llvm.copysign.f32",
        sym::copysignf64 => "llvm.copysign.f64",
        sym::floorf32 => "llvm.floor.f32",
        sym::floorf64 => "llvm.floor.f64",
        sym::ceilf32 => "llvm.ceil.f32",
        sym::ceilf64 => "llvm.ceil.f64",
        sym::truncf32 => "llvm.trunc.f32",
        sym::truncf64 => "llvm.trunc.f64",
        sym::rintf32 => "llvm.rint.f32",
        sym::rintf64 => "llvm.rint.f64",
        sym::nearbyintf32 => "llvm.nearbyint.f32",
        sym::nearbyintf64 => "llvm.nearbyint.f64",
        sym::roundf32 => "llvm.round.f32",
        sym::roundf64 => "llvm.round.f64",
        sym::ptr_mask => "llvm.ptrmask",
        _ => return None,
    };
    Some(cx.get_intrinsic(llvm_name))
}

impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
    fn codegen_intrinsic_call(
        &mut self,
        instance: ty::Instance<'tcx>,
        fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
        args: &[OperandRef<'tcx, &'ll Value>],
        llresult: &'ll Value,
        span: Span,
    ) {
        let tcx = self.tcx;
        let callee_ty = instance.ty(tcx, ty::ParamEnv::reveal_all());

        let ty::FnDef(def_id, substs) = *callee_ty.kind() else {
            bug!("expected fn item type, found {}", callee_ty);
        };

        let sig = callee_ty.fn_sig(tcx);
        let sig = tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), sig);
        let arg_tys = sig.inputs();
        let ret_ty = sig.output();
        let name = tcx.item_name(def_id);

        let llret_ty = self.layout_of(ret_ty).llvm_type(self);
        let result = PlaceRef::new_sized(llresult, fn_abi.ret.layout);

        let simple = get_simple_intrinsic(self, name);
        let llval = match name {
            _ if simple.is_some() => {
                let (simple_ty, simple_fn) = simple.unwrap();
                self.call(
                    simple_ty,
                    None,
                    simple_fn,
                    &args.iter().map(|arg| arg.immediate()).collect::<Vec<_>>(),
                    None,
                )
            }
            sym::likely => {
                self.call_intrinsic("llvm.expect.i1", &[args[0].immediate(), self.const_bool(true)])
            }
            sym::unlikely => self
                .call_intrinsic("llvm.expect.i1", &[args[0].immediate(), self.const_bool(false)]),
            kw::Try => {
                try_intrinsic(
                    self,
                    args[0].immediate(),
                    args[1].immediate(),
                    args[2].immediate(),
                    llresult,
                );
                return;
            }
            sym::breakpoint => self.call_intrinsic("llvm.debugtrap", &[]),
            sym::va_copy => {
                self.call_intrinsic("llvm.va_copy", &[args[0].immediate(), args[1].immediate()])
            }
            sym::va_arg => {
                match fn_abi.ret.layout.abi {
                    abi::Abi::Scalar(scalar) => {
                        match scalar.primitive() {
                            Primitive::Int(..) => {
                                if self.cx().size_of(ret_ty).bytes() < 4 {
                                    // `va_arg` should not be called on an integer type
                                    // less than 4 bytes in length. If it is, promote
                                    // the integer to an `i32` and truncate the result
                                    // back to the smaller type.
                                    let promoted_result = emit_va_arg(self, args[0], tcx.types.i32);
                                    self.trunc(promoted_result, llret_ty)
                                } else {
                                    emit_va_arg(self, args[0], ret_ty)
                                }
                            }
                            Primitive::F64 | Primitive::Pointer => {
                                emit_va_arg(self, args[0], ret_ty)
                            }
                            // `va_arg` should never be used with the return type f32.
                            Primitive::F32 => bug!("the va_arg intrinsic does not work with `f32`"),
                        }
                    }
                    _ => bug!("the va_arg intrinsic does not work with non-scalar types"),
                }
            }

            sym::volatile_load | sym::unaligned_volatile_load => {
                let tp_ty = substs.type_at(0);
                let ptr = args[0].immediate();
                let load = if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
                    let llty = ty.llvm_type(self);
                    let ptr = self.pointercast(ptr, self.type_ptr_to(llty));
                    self.volatile_load(llty, ptr)
                } else {
                    self.volatile_load(self.layout_of(tp_ty).llvm_type(self), ptr)
                };
                let align = if name == sym::unaligned_volatile_load {
                    1
                } else {
                    self.align_of(tp_ty).bytes() as u32
                };
                unsafe {
                    llvm::LLVMSetAlignment(load, align);
                }
                self.to_immediate(load, self.layout_of(tp_ty))
            }
            sym::volatile_store => {
                let dst = args[0].deref(self.cx());
                args[1].val.volatile_store(self, dst);
                return;
            }
            sym::unaligned_volatile_store => {
                let dst = args[0].deref(self.cx());
                args[1].val.unaligned_volatile_store(self, dst);
                return;
            }
            sym::prefetch_read_data
            | sym::prefetch_write_data
            | sym::prefetch_read_instruction
            | sym::prefetch_write_instruction => {
                let (rw, cache_type) = match name {
                    sym::prefetch_read_data => (0, 1),
                    sym::prefetch_write_data => (1, 1),
                    sym::prefetch_read_instruction => (0, 0),
                    sym::prefetch_write_instruction => (1, 0),
                    _ => bug!(),
                };
                self.call_intrinsic(
                    "llvm.prefetch",
                    &[
                        args[0].immediate(),
                        self.const_i32(rw),
                        args[1].immediate(),
                        self.const_i32(cache_type),
                    ],
                )
            }
            sym::ctlz
            | sym::ctlz_nonzero
            | sym::cttz
            | sym::cttz_nonzero
            | sym::ctpop
            | sym::bswap
            | sym::bitreverse
            | sym::rotate_left
            | sym::rotate_right
            | sym::saturating_add
            | sym::saturating_sub => {
                let ty = arg_tys[0];
                match int_type_width_signed(ty, self) {
                    Some((width, signed)) => match name {
                        sym::ctlz | sym::cttz => {
                            let y = self.const_bool(false);
                            self.call_intrinsic(
                                &format!("llvm.{}.i{}", name, width),
                                &[args[0].immediate(), y],
                            )
                        }
                        sym::ctlz_nonzero => {
                            let y = self.const_bool(true);
                            let llvm_name = &format!("llvm.ctlz.i{}", width);
                            self.call_intrinsic(llvm_name, &[args[0].immediate(), y])
                        }
                        sym::cttz_nonzero => {
                            let y = self.const_bool(true);
                            let llvm_name = &format!("llvm.cttz.i{}", width);
                            self.call_intrinsic(llvm_name, &[args[0].immediate(), y])
                        }
                        sym::ctpop => self.call_intrinsic(
                            &format!("llvm.ctpop.i{}", width),
                            &[args[0].immediate()],
                        ),
                        sym::bswap => {
                            if width == 8 {
                                args[0].immediate() // byte swap a u8/i8 is just a no-op
                            } else {
                                self.call_intrinsic(
                                    &format!("llvm.bswap.i{}", width),
                                    &[args[0].immediate()],
                                )
                            }
                        }
                        sym::bitreverse => self.call_intrinsic(
                            &format!("llvm.bitreverse.i{}", width),
                            &[args[0].immediate()],
                        ),
                        sym::rotate_left | sym::rotate_right => {
                            let is_left = name == sym::rotate_left;
                            let val = args[0].immediate();
                            let raw_shift = args[1].immediate();
                            // rotate = funnel shift with first two args the same
                            let llvm_name =
                                &format!("llvm.fsh{}.i{}", if is_left { 'l' } else { 'r' }, width);
                            self.call_intrinsic(llvm_name, &[val, val, raw_shift])
                        }
                        sym::saturating_add | sym::saturating_sub => {
                            let is_add = name == sym::saturating_add;
                            let lhs = args[0].immediate();
                            let rhs = args[1].immediate();
                            let llvm_name = &format!(
                                "llvm.{}{}.sat.i{}",
                                if signed { 's' } else { 'u' },
                                if is_add { "add" } else { "sub" },
                                width
                            );
                            self.call_intrinsic(llvm_name, &[lhs, rhs])
                        }
                        _ => bug!(),
                    },
                    None => {
                        span_invalid_monomorphization_error(
                            tcx.sess,
                            span,
                            &format!(
                                "invalid monomorphization of `{}` intrinsic: \
                                      expected basic integer type, found `{}`",
                                name, ty
                            ),
                        );
                        return;
                    }
                }
            }

            sym::raw_eq => {
                use abi::Abi::*;
                let tp_ty = substs.type_at(0);
                let layout = self.layout_of(tp_ty).layout;
                let use_integer_compare = match layout.abi() {
                    Scalar(_) | ScalarPair(_, _) => true,
                    Uninhabited | Vector { .. } => false,
                    Aggregate { .. } => {
                        // For rusty ABIs, small aggregates are actually passed
                        // as `RegKind::Integer` (see `FnAbi::adjust_for_abi`),
                        // so we re-use that same threshold here.
                        layout.size() <= self.data_layout().pointer_size * 2
                    }
                };

                let a = args[0].immediate();
                let b = args[1].immediate();
                if layout.size().bytes() == 0 {
                    self.const_bool(true)
                } else if use_integer_compare {
                    let integer_ty = self.type_ix(layout.size().bits());
                    let ptr_ty = self.type_ptr_to(integer_ty);
                    let a_ptr = self.bitcast(a, ptr_ty);
                    let a_val = self.load(integer_ty, a_ptr, layout.align().abi);
                    let b_ptr = self.bitcast(b, ptr_ty);
                    let b_val = self.load(integer_ty, b_ptr, layout.align().abi);
                    self.icmp(IntPredicate::IntEQ, a_val, b_val)
                } else {
                    let i8p_ty = self.type_i8p();
                    let a_ptr = self.bitcast(a, i8p_ty);
                    let b_ptr = self.bitcast(b, i8p_ty);
                    let n = self.const_usize(layout.size().bytes());
                    let cmp = self.call_intrinsic("memcmp", &[a_ptr, b_ptr, n]);
                    match self.cx.sess().target.arch.as_ref() {
                        "avr" | "msp430" => self.icmp(IntPredicate::IntEQ, cmp, self.const_i16(0)),
                        _ => self.icmp(IntPredicate::IntEQ, cmp, self.const_i32(0)),
                    }
                }
            }

            sym::black_box => {
                args[0].val.store(self, result);
                let result_val_span = [result.llval];
                // We need to "use" the argument in some way LLVM can't introspect, and on
                // targets that support it we can typically leverage inline assembly to do
                // this. LLVM's interpretation of inline assembly is that it's, well, a black
                // box. This isn't the greatest implementation since it probably deoptimizes
                // more than we want, but it's so far good enough.
                //
                // For zero-sized types, the location pointed to by the result may be
                // uninitialized. Do not "use" the result in this case; instead just clobber
                // the memory.
                let (constraint, inputs): (&str, &[_]) = if result.layout.is_zst() {
                    ("~{memory}", &[])
                } else {
                    ("r,~{memory}", &result_val_span)
                };
                crate::asm::inline_asm_call(
                    self,
                    "",
                    constraint,
                    inputs,
                    self.type_void(),
                    true,
                    false,
                    llvm::AsmDialect::Att,
                    &[span],
                    false,
                    None,
                )
                .unwrap_or_else(|| bug!("failed to generate inline asm call for `black_box`"));

                // We have copied the value to `result` already.
                return;
            }

            _ if name.as_str().starts_with("simd_") => {
                match generic_simd_intrinsic(self, name, callee_ty, args, ret_ty, llret_ty, span) {
                    Ok(llval) => llval,
                    Err(()) => return,
                }
            }

            _ => bug!("unknown intrinsic '{}'", name),
        };

        if !fn_abi.ret.is_ignore() {
            if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
                let ptr_llty = self.type_ptr_to(ty.llvm_type(self));
                let ptr = self.pointercast(result.llval, ptr_llty);
                self.store(llval, ptr, result.align);
            } else {
                OperandRef::from_immediate_or_packed_pair(self, llval, result.layout)
                    .val
                    .store(self, result);
            }
        }
    }

    fn abort(&mut self) {
        self.call_intrinsic("llvm.trap", &[]);
    }

    fn assume(&mut self, val: Self::Value) {
        self.call_intrinsic("llvm.assume", &[val]);
    }

    fn expect(&mut self, cond: Self::Value, expected: bool) -> Self::Value {
        self.call_intrinsic("llvm.expect.i1", &[cond, self.const_bool(expected)])
    }

    fn type_test(&mut self, pointer: Self::Value, typeid: Self::Value) -> Self::Value {
        // Test the called operand using llvm.type.test intrinsic. The LowerTypeTests link-time
        // optimization pass replaces calls to this intrinsic with code to test type membership.
        let i8p_ty = self.type_i8p();
        let bitcast = self.bitcast(pointer, i8p_ty);
        self.call_intrinsic("llvm.type.test", &[bitcast, typeid])
    }

    fn type_checked_load(
        &mut self,
        llvtable: &'ll Value,
        vtable_byte_offset: u64,
        typeid: &'ll Value,
    ) -> Self::Value {
        let vtable_byte_offset = self.const_i32(vtable_byte_offset as i32);
        self.call_intrinsic("llvm.type.checked.load", &[llvtable, vtable_byte_offset, typeid])
    }

    fn va_start(&mut self, va_list: &'ll Value) -> &'ll Value {
        self.call_intrinsic("llvm.va_start", &[va_list])
    }

    fn va_end(&mut self, va_list: &'ll Value) -> &'ll Value {
        self.call_intrinsic("llvm.va_end", &[va_list])
    }
}

fn try_intrinsic<'ll>(
    bx: &mut Builder<'_, 'll, '_>,
    try_func: &'ll Value,
    data: &'ll Value,
    catch_func: &'ll Value,
    dest: &'ll Value,
) {
    if bx.sess().panic_strategy() == PanicStrategy::Abort {
        let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
        bx.call(try_func_ty, None, try_func, &[data], None);
        // Return 0 unconditionally from the intrinsic call;
        // we can never unwind.
        let ret_align = bx.tcx().data_layout.i32_align.abi;
        bx.store(bx.const_i32(0), dest, ret_align);
    } else if wants_msvc_seh(bx.sess()) {
        codegen_msvc_try(bx, try_func, data, catch_func, dest);
    } else if bx.sess().target.os == "emscripten" {
        codegen_emcc_try(bx, try_func, data, catch_func, dest);
    } else {
        codegen_gnu_try(bx, try_func, data, catch_func, dest);
    }
}

// MSVC's definition of the `rust_try` function.
//
// This implementation uses the new exception handling instructions in LLVM
// which have support in LLVM for SEH on MSVC targets. Although these
// instructions are meant to work for all targets, as of the time of this
// writing, however, LLVM does not recommend the usage of these new instructions
// as the old ones are still more optimized.
fn codegen_msvc_try<'ll>(
    bx: &mut Builder<'_, 'll, '_>,
    try_func: &'ll Value,
    data: &'ll Value,
    catch_func: &'ll Value,
    dest: &'ll Value,
) {
    let (llty, llfn) = get_rust_try_fn(bx, &mut |mut bx| {
        bx.set_personality_fn(bx.eh_personality());

        let normal = bx.append_sibling_block("normal");
        let catchswitch = bx.append_sibling_block("catchswitch");
        let catchpad_rust = bx.append_sibling_block("catchpad_rust");
        let catchpad_foreign = bx.append_sibling_block("catchpad_foreign");
        let caught = bx.append_sibling_block("caught");

        let try_func = llvm::get_param(bx.llfn(), 0);
        let data = llvm::get_param(bx.llfn(), 1);
        let catch_func = llvm::get_param(bx.llfn(), 2);

        // We're generating an IR snippet that looks like:
        //
        //   declare i32 @rust_try(%try_func, %data, %catch_func) {
        //      %slot = alloca i8*
        //      invoke %try_func(%data) to label %normal unwind label %catchswitch
        //
        //   normal:
        //      ret i32 0
        //
        //   catchswitch:
        //      %cs = catchswitch within none [%catchpad_rust, %catchpad_foreign] unwind to caller
        //
        //   catchpad_rust:
        //      %tok = catchpad within %cs [%type_descriptor, 8, %slot]
        //      %ptr = load %slot
        //      call %catch_func(%data, %ptr)
        //      catchret from %tok to label %caught
        //
        //   catchpad_foreign:
        //      %tok = catchpad within %cs [null, 64, null]
        //      call %catch_func(%data, null)
        //      catchret from %tok to label %caught
        //
        //   caught:
        //      ret i32 1
        //   }
        //
        // This structure follows the basic usage of throw/try/catch in LLVM.
        // For example, compile this C++ snippet to see what LLVM generates:
        //
        //      struct rust_panic {
        //          rust_panic(const rust_panic&);
        //          ~rust_panic();
        //
        //          void* x[2];
        //      };
        //
        //      int __rust_try(
        //          void (*try_func)(void*),
        //          void *data,
        //          void (*catch_func)(void*, void*) noexcept
        //      ) {
        //          try {
        //              try_func(data);
        //              return 0;
        //          } catch(rust_panic& a) {
        //              catch_func(data, &a);
        //              return 1;
        //          } catch(...) {
        //              catch_func(data, NULL);
        //              return 1;
        //          }
        //      }
        //
        // More information can be found in libstd's seh.rs implementation.
        let ptr_align = bx.tcx().data_layout.pointer_align.abi;
        let slot = bx.alloca(bx.type_i8p(), ptr_align);
        let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
        bx.invoke(try_func_ty, None, try_func, &[data], normal, catchswitch, None);

        bx.switch_to_block(normal);
        bx.ret(bx.const_i32(0));

        bx.switch_to_block(catchswitch);
        let cs = bx.catch_switch(None, None, &[catchpad_rust, catchpad_foreign]);

        // We can't use the TypeDescriptor defined in libpanic_unwind because it
        // might be in another DLL and the SEH encoding only supports specifying
        // a TypeDescriptor from the current module.
        //
        // However this isn't an issue since the MSVC runtime uses string
        // comparison on the type name to match TypeDescriptors rather than
        // pointer equality.
        //
        // So instead we generate a new TypeDescriptor in each module that uses
        // `try` and let the linker merge duplicate definitions in the same
        // module.
        //
        // When modifying, make sure that the type_name string exactly matches
        // the one used in src/libpanic_unwind/seh.rs.
        let type_info_vtable = bx.declare_global("??_7type_info@@6B@", bx.type_i8p());
        let type_name = bx.const_bytes(b"rust_panic\0");
        let type_info =
            bx.const_struct(&[type_info_vtable, bx.const_null(bx.type_i8p()), type_name], false);
        let tydesc = bx.declare_global("__rust_panic_type_info", bx.val_ty(type_info));
        unsafe {
            llvm::LLVMRustSetLinkage(tydesc, llvm::Linkage::LinkOnceODRLinkage);
            llvm::SetUniqueComdat(bx.llmod, tydesc);
            llvm::LLVMSetInitializer(tydesc, type_info);
        }

        // The flag value of 8 indicates that we are catching the exception by
        // reference instead of by value. We can't use catch by value because
        // that requires copying the exception object, which we don't support
        // since our exception object effectively contains a Box.
        //
        // Source: MicrosoftCXXABI::getAddrOfCXXCatchHandlerType in clang
        bx.switch_to_block(catchpad_rust);
        let flags = bx.const_i32(8);
        let funclet = bx.catch_pad(cs, &[tydesc, flags, slot]);
        let ptr = bx.load(bx.type_i8p(), slot, ptr_align);
        let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
        bx.call(catch_ty, None, catch_func, &[data, ptr], Some(&funclet));
        bx.catch_ret(&funclet, caught);

        // The flag value of 64 indicates a "catch-all".
        bx.switch_to_block(catchpad_foreign);
        let flags = bx.const_i32(64);
        let null = bx.const_null(bx.type_i8p());
        let funclet = bx.catch_pad(cs, &[null, flags, null]);
        bx.call(catch_ty, None, catch_func, &[data, null], Some(&funclet));
        bx.catch_ret(&funclet, caught);

        bx.switch_to_block(caught);
        bx.ret(bx.const_i32(1));
    });

    // Note that no invoke is used here because by definition this function
    // can't panic (that's what it's catching).
    let ret = bx.call(llty, None, llfn, &[try_func, data, catch_func], None);
    let i32_align = bx.tcx().data_layout.i32_align.abi;
    bx.store(ret, dest, i32_align);
}

// Definition of the standard `try` function for Rust using the GNU-like model
// of exceptions (e.g., the normal semantics of LLVM's `landingpad` and `invoke`
// instructions).
//
// This codegen is a little surprising because we always call a shim
// function instead of inlining the call to `invoke` manually here. This is done
// because in LLVM we're only allowed to have one personality per function
// definition. The call to the `try` intrinsic is being inlined into the
// function calling it, and that function may already have other personality
// functions in play. By calling a shim we're guaranteed that our shim will have
// the right personality function.
fn codegen_gnu_try<'ll>(
    bx: &mut Builder<'_, 'll, '_>,
    try_func: &'ll Value,
    data: &'ll Value,
    catch_func: &'ll Value,
    dest: &'ll Value,
) {
    let (llty, llfn) = get_rust_try_fn(bx, &mut |mut bx| {
        // Codegens the shims described above:
        //
        //   bx:
        //      invoke %try_func(%data) normal %normal unwind %catch
        //
        //   normal:
        //      ret 0
        //
        //   catch:
        //      (%ptr, _) = landingpad
        //      call %catch_func(%data, %ptr)
        //      ret 1
        let then = bx.append_sibling_block("then");
        let catch = bx.append_sibling_block("catch");

        let try_func = llvm::get_param(bx.llfn(), 0);
        let data = llvm::get_param(bx.llfn(), 1);
        let catch_func = llvm::get_param(bx.llfn(), 2);
        let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
        bx.invoke(try_func_ty, None, try_func, &[data], then, catch, None);

        bx.switch_to_block(then);
        bx.ret(bx.const_i32(0));

        // Type indicator for the exception being thrown.
        //
        // The first value in this tuple is a pointer to the exception object
        // being thrown.  The second value is a "selector" indicating which of
        // the landing pad clauses the exception's type had been matched to.
        // rust_try ignores the selector.
        bx.switch_to_block(catch);
        let lpad_ty = bx.type_struct(&[bx.type_i8p(), bx.type_i32()], false);
        let vals = bx.landing_pad(lpad_ty, bx.eh_personality(), 1);
        let tydesc = bx.const_null(bx.type_i8p());
        bx.add_clause(vals, tydesc);
        let ptr = bx.extract_value(vals, 0);
        let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
        bx.call(catch_ty, None, catch_func, &[data, ptr], None);
        bx.ret(bx.const_i32(1));
    });

    // Note that no invoke is used here because by definition this function
    // can't panic (that's what it's catching).
    let ret = bx.call(llty, None, llfn, &[try_func, data, catch_func], None);
    let i32_align = bx.tcx().data_layout.i32_align.abi;
    bx.store(ret, dest, i32_align);
}

// Variant of codegen_gnu_try used for emscripten where Rust panics are
// implemented using C++ exceptions. Here we use exceptions of a specific type
// (`struct rust_panic`) to represent Rust panics.
fn codegen_emcc_try<'ll>(
    bx: &mut Builder<'_, 'll, '_>,
    try_func: &'ll Value,
    data: &'ll Value,
    catch_func: &'ll Value,
    dest: &'ll Value,
) {
    let (llty, llfn) = get_rust_try_fn(bx, &mut |mut bx| {
        // Codegens the shims described above:
        //
        //   bx:
        //      invoke %try_func(%data) normal %normal unwind %catch
        //
        //   normal:
        //      ret 0
        //
        //   catch:
        //      (%ptr, %selector) = landingpad
        //      %rust_typeid = @llvm.eh.typeid.for(@_ZTI10rust_panic)
        //      %is_rust_panic = %selector == %rust_typeid
        //      %catch_data = alloca { i8*, i8 }
        //      %catch_data[0] = %ptr
        //      %catch_data[1] = %is_rust_panic
        //      call %catch_func(%data, %catch_data)
        //      ret 1
        let then = bx.append_sibling_block("then");
        let catch = bx.append_sibling_block("catch");

        let try_func = llvm::get_param(bx.llfn(), 0);
        let data = llvm::get_param(bx.llfn(), 1);
        let catch_func = llvm::get_param(bx.llfn(), 2);
        let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
        bx.invoke(try_func_ty, None, try_func, &[data], then, catch, None);

        bx.switch_to_block(then);
        bx.ret(bx.const_i32(0));

        // Type indicator for the exception being thrown.
        //
        // The first value in this tuple is a pointer to the exception object
        // being thrown.  The second value is a "selector" indicating which of
        // the landing pad clauses the exception's type had been matched to.
        bx.switch_to_block(catch);
        let tydesc = bx.eh_catch_typeinfo();
        let lpad_ty = bx.type_struct(&[bx.type_i8p(), bx.type_i32()], false);
        let vals = bx.landing_pad(lpad_ty, bx.eh_personality(), 2);
        bx.add_clause(vals, tydesc);
        bx.add_clause(vals, bx.const_null(bx.type_i8p()));
        let ptr = bx.extract_value(vals, 0);
        let selector = bx.extract_value(vals, 1);

        // Check if the typeid we got is the one for a Rust panic.
        let rust_typeid = bx.call_intrinsic("llvm.eh.typeid.for", &[tydesc]);
        let is_rust_panic = bx.icmp(IntPredicate::IntEQ, selector, rust_typeid);
        let is_rust_panic = bx.zext(is_rust_panic, bx.type_bool());

        // We need to pass two values to catch_func (ptr and is_rust_panic), so
        // create an alloca and pass a pointer to that.
        let ptr_align = bx.tcx().data_layout.pointer_align.abi;
        let i8_align = bx.tcx().data_layout.i8_align.abi;
        let catch_data_type = bx.type_struct(&[bx.type_i8p(), bx.type_bool()], false);
        let catch_data = bx.alloca(catch_data_type, ptr_align);
        let catch_data_0 =
            bx.inbounds_gep(catch_data_type, catch_data, &[bx.const_usize(0), bx.const_usize(0)]);
        bx.store(ptr, catch_data_0, ptr_align);
        let catch_data_1 =
            bx.inbounds_gep(catch_data_type, catch_data, &[bx.const_usize(0), bx.const_usize(1)]);
        bx.store(is_rust_panic, catch_data_1, i8_align);
        let catch_data = bx.bitcast(catch_data, bx.type_i8p());

        let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
        bx.call(catch_ty, None, catch_func, &[data, catch_data], None);
        bx.ret(bx.const_i32(1));
    });

    // Note that no invoke is used here because by definition this function
    // can't panic (that's what it's catching).
    let ret = bx.call(llty, None, llfn, &[try_func, data, catch_func], None);
    let i32_align = bx.tcx().data_layout.i32_align.abi;
    bx.store(ret, dest, i32_align);
}

// Helper function to give a Block to a closure to codegen a shim function.
// This is currently primarily used for the `try` intrinsic functions above.
fn gen_fn<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    name: &str,
    rust_fn_sig: ty::PolyFnSig<'tcx>,
    codegen: &mut dyn FnMut(Builder<'_, 'll, 'tcx>),
) -> (&'ll Type, &'ll Value) {
    let fn_abi = cx.fn_abi_of_fn_ptr(rust_fn_sig, ty::List::empty());
    let llty = fn_abi.llvm_type(cx);
    let llfn = cx.declare_fn(name, fn_abi);
    cx.set_frame_pointer_type(llfn);
    cx.apply_target_cpu_attr(llfn);
    // FIXME(eddyb) find a nicer way to do this.
    unsafe { llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::InternalLinkage) };
    let llbb = Builder::append_block(cx, llfn, "entry-block");
    let bx = Builder::build(cx, llbb);
    codegen(bx);
    (llty, llfn)
}

// Helper function used to get a handle to the `__rust_try` function used to
// catch exceptions.
//
// This function is only generated once and is then cached.
fn get_rust_try_fn<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    codegen: &mut dyn FnMut(Builder<'_, 'll, 'tcx>),
) -> (&'ll Type, &'ll Value) {
    if let Some(llfn) = cx.rust_try_fn.get() {
        return llfn;
    }

    // Define the type up front for the signature of the rust_try function.
    let tcx = cx.tcx;
    let i8p = tcx.mk_mut_ptr(tcx.types.i8);
    // `unsafe fn(*mut i8) -> ()`
    let try_fn_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
        iter::once(i8p),
        tcx.mk_unit(),
        false,
        hir::Unsafety::Unsafe,
        Abi::Rust,
    )));
    // `unsafe fn(*mut i8, *mut i8) -> ()`
    let catch_fn_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
        [i8p, i8p].iter().cloned(),
        tcx.mk_unit(),
        false,
        hir::Unsafety::Unsafe,
        Abi::Rust,
    )));
    // `unsafe fn(unsafe fn(*mut i8) -> (), *mut i8, unsafe fn(*mut i8, *mut i8) -> ()) -> i32`
    let rust_fn_sig = ty::Binder::dummy(cx.tcx.mk_fn_sig(
        [try_fn_ty, i8p, catch_fn_ty].into_iter(),
        tcx.types.i32,
        false,
        hir::Unsafety::Unsafe,
        Abi::Rust,
    ));
    let rust_try = gen_fn(cx, "__rust_try", rust_fn_sig, codegen);
    cx.rust_try_fn.set(Some(rust_try));
    rust_try
}

fn generic_simd_intrinsic<'ll, 'tcx>(
    bx: &mut Builder<'_, 'll, 'tcx>,
    name: Symbol,
    callee_ty: Ty<'tcx>,
    args: &[OperandRef<'tcx, &'ll Value>],
    ret_ty: Ty<'tcx>,
    llret_ty: &'ll Type,
    span: Span,
) -> Result<&'ll Value, ()> {
    // macros for error handling:
    #[allow(unused_macro_rules)]
    macro_rules! emit_error {
        ($msg: tt) => {
            emit_error!($msg, )
        };
        ($msg: tt, $($fmt: tt)*) => {
            span_invalid_monomorphization_error(
                bx.sess(), span,
                &format!(concat!("invalid monomorphization of `{}` intrinsic: ", $msg),
                         name, $($fmt)*));
        }
    }

    macro_rules! return_error {
        ($($fmt: tt)*) => {
            {
                emit_error!($($fmt)*);
                return Err(());
            }
        }
    }

    macro_rules! require {
        ($cond: expr, $($fmt: tt)*) => {
            if !$cond {
                return_error!($($fmt)*);
            }
        };
    }

    macro_rules! require_simd {
        ($ty: expr, $position: expr) => {
            require!($ty.is_simd(), "expected SIMD {} type, found non-SIMD `{}`", $position, $ty)
        };
    }

    let tcx = bx.tcx();
    let sig =
        tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), callee_ty.fn_sig(tcx));
    let arg_tys = sig.inputs();

    if name == sym::simd_select_bitmask {
        require_simd!(arg_tys[1], "argument");
        let (len, _) = arg_tys[1].simd_size_and_type(bx.tcx());

        let expected_int_bits = (len.max(8) - 1).next_power_of_two();
        let expected_bytes = len / 8 + ((len % 8 > 0) as u64);

        let mask_ty = arg_tys[0];
        let mask = match mask_ty.kind() {
            ty::Int(i) if i.bit_width() == Some(expected_int_bits) => args[0].immediate(),
            ty::Uint(i) if i.bit_width() == Some(expected_int_bits) => args[0].immediate(),
            ty::Array(elem, len)
                if matches!(elem.kind(), ty::Uint(ty::UintTy::U8))
                    && len.try_eval_usize(bx.tcx, ty::ParamEnv::reveal_all())
                        == Some(expected_bytes) =>
            {
                let place = PlaceRef::alloca(bx, args[0].layout);
                args[0].val.store(bx, place);
                let int_ty = bx.type_ix(expected_bytes * 8);
                let ptr = bx.pointercast(place.llval, bx.cx.type_ptr_to(int_ty));
                bx.load(int_ty, ptr, Align::ONE)
            }
            _ => return_error!(
                "invalid bitmask `{}`, expected `u{}` or `[u8; {}]`",
                mask_ty,
                expected_int_bits,
                expected_bytes
            ),
        };

        let i1 = bx.type_i1();
        let im = bx.type_ix(len);
        let i1xn = bx.type_vector(i1, len);
        let m_im = bx.trunc(mask, im);
        let m_i1s = bx.bitcast(m_im, i1xn);
        return Ok(bx.select(m_i1s, args[1].immediate(), args[2].immediate()));
    }

    // every intrinsic below takes a SIMD vector as its first argument
    require_simd!(arg_tys[0], "input");
    let in_ty = arg_tys[0];

    let comparison = match name {
        sym::simd_eq => Some(hir::BinOpKind::Eq),
        sym::simd_ne => Some(hir::BinOpKind::Ne),
        sym::simd_lt => Some(hir::BinOpKind::Lt),
        sym::simd_le => Some(hir::BinOpKind::Le),
        sym::simd_gt => Some(hir::BinOpKind::Gt),
        sym::simd_ge => Some(hir::BinOpKind::Ge),
        _ => None,
    };

    let (in_len, in_elem) = arg_tys[0].simd_size_and_type(bx.tcx());
    if let Some(cmp_op) = comparison {
        require_simd!(ret_ty, "return");

        let (out_len, out_ty) = ret_ty.simd_size_and_type(bx.tcx());
        require!(
            in_len == out_len,
            "expected return type with length {} (same as input type `{}`), \
             found `{}` with length {}",
            in_len,
            in_ty,
            ret_ty,
            out_len
        );
        require!(
            bx.type_kind(bx.element_type(llret_ty)) == TypeKind::Integer,
            "expected return type with integer elements, found `{}` with non-integer `{}`",
            ret_ty,
            out_ty
        );

        return Ok(compare_simd_types(
            bx,
            args[0].immediate(),
            args[1].immediate(),
            in_elem,
            llret_ty,
            cmp_op,
        ));
    }

    if let Some(stripped) = name.as_str().strip_prefix("simd_shuffle") {
        // If this intrinsic is the older "simd_shuffleN" form, simply parse the integer.
        // If there is no suffix, use the index array length.
        let n: u64 = if stripped.is_empty() {
            // Make sure this is actually an array, since typeck only checks the length-suffixed
            // version of this intrinsic.
            match args[2].layout.ty.kind() {
                ty::Array(ty, len) if matches!(ty.kind(), ty::Uint(ty::UintTy::U32)) => {
                    len.try_eval_usize(bx.cx.tcx, ty::ParamEnv::reveal_all()).unwrap_or_else(|| {
                        span_bug!(span, "could not evaluate shuffle index array length")
                    })
                }
                _ => return_error!(
                    "simd_shuffle index must be an array of `u32`, got `{}`",
                    args[2].layout.ty
                ),
            }
        } else {
            stripped.parse().unwrap_or_else(|_| {
                span_bug!(span, "bad `simd_shuffle` instruction only caught in codegen?")
            })
        };

        require_simd!(ret_ty, "return");
        let (out_len, out_ty) = ret_ty.simd_size_and_type(bx.tcx());
        require!(
            out_len == n,
            "expected return type of length {}, found `{}` with length {}",
            n,
            ret_ty,
            out_len
        );
        require!(
            in_elem == out_ty,
            "expected return element type `{}` (element of input `{}`), \
             found `{}` with element type `{}`",
            in_elem,
            in_ty,
            ret_ty,
            out_ty
        );

        let total_len = u128::from(in_len) * 2;

        let vector = args[2].immediate();

        let indices: Option<Vec<_>> = (0..n)
            .map(|i| {
                let arg_idx = i;
                let val = bx.const_get_elt(vector, i as u64);
                match bx.const_to_opt_u128(val, true) {
                    None => {
                        emit_error!("shuffle index #{} is not a constant", arg_idx);
                        None
                    }
                    Some(idx) if idx >= total_len => {
                        emit_error!(
                            "shuffle index #{} is out of bounds (limit {})",
                            arg_idx,
                            total_len
                        );
                        None
                    }
                    Some(idx) => Some(bx.const_i32(idx as i32)),
                }
            })
            .collect();
        let Some(indices) = indices else {
            return Ok(bx.const_null(llret_ty));
        };

        return Ok(bx.shuffle_vector(
            args[0].immediate(),
            args[1].immediate(),
            bx.const_vector(&indices),
        ));
    }

    if name == sym::simd_insert {
        require!(
            in_elem == arg_tys[2],
            "expected inserted type `{}` (element of input `{}`), found `{}`",
            in_elem,
            in_ty,
            arg_tys[2]
        );
        return Ok(bx.insert_element(
            args[0].immediate(),
            args[2].immediate(),
            args[1].immediate(),
        ));
    }
    if name == sym::simd_extract {
        require!(
            ret_ty == in_elem,
            "expected return type `{}` (element of input `{}`), found `{}`",
            in_elem,
            in_ty,
            ret_ty
        );
        return Ok(bx.extract_element(args[0].immediate(), args[1].immediate()));
    }

    if name == sym::simd_select {
        let m_elem_ty = in_elem;
        let m_len = in_len;
        require_simd!(arg_tys[1], "argument");
        let (v_len, _) = arg_tys[1].simd_size_and_type(bx.tcx());
        require!(
            m_len == v_len,
            "mismatched lengths: mask length `{}` != other vector length `{}`",
            m_len,
            v_len
        );
        match m_elem_ty.kind() {
            ty::Int(_) => {}
            _ => return_error!("mask element type is `{}`, expected `i_`", m_elem_ty),
        }
        // truncate the mask to a vector of i1s
        let i1 = bx.type_i1();
        let i1xn = bx.type_vector(i1, m_len as u64);
        let m_i1s = bx.trunc(args[0].immediate(), i1xn);
        return Ok(bx.select(m_i1s, args[1].immediate(), args[2].immediate()));
    }

    if name == sym::simd_bitmask {
        // The `fn simd_bitmask(vector) -> unsigned integer` intrinsic takes a
        // vector mask and returns the most significant bit (MSB) of each lane in the form
        // of either:
        // * an unsigned integer
        // * an array of `u8`
        // If the vector has less than 8 lanes, a u8 is returned with zeroed trailing bits.
        //
        // The bit order of the result depends on the byte endianness, LSB-first for little
        // endian and MSB-first for big endian.
        let expected_int_bits = in_len.max(8);
        let expected_bytes = expected_int_bits / 8 + ((expected_int_bits % 8 > 0) as u64);

        // Integer vector <i{in_bitwidth} x in_len>:
        let (i_xn, in_elem_bitwidth) = match in_elem.kind() {
            ty::Int(i) => (
                args[0].immediate(),
                i.bit_width().unwrap_or_else(|| bx.data_layout().pointer_size.bits()),
            ),
            ty::Uint(i) => (
                args[0].immediate(),
                i.bit_width().unwrap_or_else(|| bx.data_layout().pointer_size.bits()),
            ),
            _ => return_error!(
                "vector argument `{}`'s element type `{}`, expected integer element type",
                in_ty,
                in_elem
            ),
        };

        // Shift the MSB to the right by "in_elem_bitwidth - 1" into the first bit position.
        let shift_indices =
            vec![
                bx.cx.const_int(bx.type_ix(in_elem_bitwidth), (in_elem_bitwidth - 1) as _);
                in_len as _
            ];
        let i_xn_msb = bx.lshr(i_xn, bx.const_vector(shift_indices.as_slice()));
        // Truncate vector to an <i1 x N>
        let i1xn = bx.trunc(i_xn_msb, bx.type_vector(bx.type_i1(), in_len));
        // Bitcast <i1 x N> to iN:
        let i_ = bx.bitcast(i1xn, bx.type_ix(in_len));

        match ret_ty.kind() {
            ty::Uint(i) if i.bit_width() == Some(expected_int_bits) => {
                // Zero-extend iN to the bitmask type:
                return Ok(bx.zext(i_, bx.type_ix(expected_int_bits)));
            }
            ty::Array(elem, len)
                if matches!(elem.kind(), ty::Uint(ty::UintTy::U8))
                    && len.try_eval_usize(bx.tcx, ty::ParamEnv::reveal_all())
                        == Some(expected_bytes) =>
            {
                // Zero-extend iN to the array length:
                let ze = bx.zext(i_, bx.type_ix(expected_bytes * 8));

                // Convert the integer to a byte array
                let ptr = bx.alloca(bx.type_ix(expected_bytes * 8), Align::ONE);
                bx.store(ze, ptr, Align::ONE);
                let array_ty = bx.type_array(bx.type_i8(), expected_bytes);
                let ptr = bx.pointercast(ptr, bx.cx.type_ptr_to(array_ty));
                return Ok(bx.load(array_ty, ptr, Align::ONE));
            }
            _ => return_error!(
                "cannot return `{}`, expected `u{}` or `[u8; {}]`",
                ret_ty,
                expected_int_bits,
                expected_bytes
            ),
        }
    }

    fn simd_simple_float_intrinsic<'ll, 'tcx>(
        name: Symbol,
        in_elem: Ty<'_>,
        in_ty: Ty<'_>,
        in_len: u64,
        bx: &mut Builder<'_, 'll, 'tcx>,
        span: Span,
        args: &[OperandRef<'tcx, &'ll Value>],
    ) -> Result<&'ll Value, ()> {
        #[allow(unused_macro_rules)]
        macro_rules! emit_error {
            ($msg: tt) => {
                emit_error!($msg, )
            };
            ($msg: tt, $($fmt: tt)*) => {
                span_invalid_monomorphization_error(
                    bx.sess(), span,
                    &format!(concat!("invalid monomorphization of `{}` intrinsic: ", $msg),
                             name, $($fmt)*));
            }
        }
        macro_rules! return_error {
            ($($fmt: tt)*) => {
                {
                    emit_error!($($fmt)*);
                    return Err(());
                }
            }
        }

        let (elem_ty_str, elem_ty) = if let ty::Float(f) = in_elem.kind() {
            let elem_ty = bx.cx.type_float_from_ty(*f);
            match f.bit_width() {
                32 => ("f32", elem_ty),
                64 => ("f64", elem_ty),
                _ => {
                    return_error!(
                        "unsupported element type `{}` of floating-point vector `{}`",
                        f.name_str(),
                        in_ty
                    );
                }
            }
        } else {
            return_error!("`{}` is not a floating-point type", in_ty);
        };

        let vec_ty = bx.type_vector(elem_ty, in_len);

        let (intr_name, fn_ty) = match name {
            sym::simd_ceil => ("ceil", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_fabs => ("fabs", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_fcos => ("cos", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_fexp2 => ("exp2", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_fexp => ("exp", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_flog10 => ("log10", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_flog2 => ("log2", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_flog => ("log", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_floor => ("floor", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_fma => ("fma", bx.type_func(&[vec_ty, vec_ty, vec_ty], vec_ty)),
            sym::simd_fpowi => ("powi", bx.type_func(&[vec_ty, bx.type_i32()], vec_ty)),
            sym::simd_fpow => ("pow", bx.type_func(&[vec_ty, vec_ty], vec_ty)),
            sym::simd_fsin => ("sin", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_fsqrt => ("sqrt", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_round => ("round", bx.type_func(&[vec_ty], vec_ty)),
            sym::simd_trunc => ("trunc", bx.type_func(&[vec_ty], vec_ty)),
            _ => return_error!("unrecognized intrinsic `{}`", name),
        };
        let llvm_name = &format!("llvm.{0}.v{1}{2}", intr_name, in_len, elem_ty_str);
        let f = bx.declare_cfn(llvm_name, llvm::UnnamedAddr::No, fn_ty);
        let c = bx.call(
            fn_ty,
            None,
            f,
            &args.iter().map(|arg| arg.immediate()).collect::<Vec<_>>(),
            None,
        );
        Ok(c)
    }

    if std::matches!(
        name,
        sym::simd_ceil
            | sym::simd_fabs
            | sym::simd_fcos
            | sym::simd_fexp2
            | sym::simd_fexp
            | sym::simd_flog10
            | sym::simd_flog2
            | sym::simd_flog
            | sym::simd_floor
            | sym::simd_fma
            | sym::simd_fpow
            | sym::simd_fpowi
            | sym::simd_fsin
            | sym::simd_fsqrt
            | sym::simd_round
            | sym::simd_trunc
    ) {
        return simd_simple_float_intrinsic(name, in_elem, in_ty, in_len, bx, span, args);
    }

    // FIXME: use:
    //  https://github.com/llvm-mirror/llvm/blob/master/include/llvm/IR/Function.h#L182
    //  https://github.com/llvm-mirror/llvm/blob/master/include/llvm/IR/Intrinsics.h#L81
    fn llvm_vector_str(
        elem_ty: Ty<'_>,
        vec_len: u64,
        no_pointers: usize,
        bx: &Builder<'_, '_, '_>,
    ) -> String {
        let p0s: String = "p0".repeat(no_pointers);
        match *elem_ty.kind() {
            ty::Int(v) => format!(
                "v{}{}i{}",
                vec_len,
                p0s,
                // Normalize to prevent crash if v: IntTy::Isize
                v.normalize(bx.target_spec().pointer_width).bit_width().unwrap()
            ),
            ty::Uint(v) => format!(
                "v{}{}i{}",
                vec_len,
                p0s,
                // Normalize to prevent crash if v: UIntTy::Usize
                v.normalize(bx.target_spec().pointer_width).bit_width().unwrap()
            ),
            ty::Float(v) => format!("v{}{}f{}", vec_len, p0s, v.bit_width()),
            _ => unreachable!(),
        }
    }

    fn llvm_vector_ty<'ll>(
        cx: &CodegenCx<'ll, '_>,
        elem_ty: Ty<'_>,
        vec_len: u64,
        mut no_pointers: usize,
    ) -> &'ll Type {
        // FIXME: use cx.layout_of(ty).llvm_type() ?
        let mut elem_ty = match *elem_ty.kind() {
            ty::Int(v) => cx.type_int_from_ty(v),
            ty::Uint(v) => cx.type_uint_from_ty(v),
            ty::Float(v) => cx.type_float_from_ty(v),
            _ => unreachable!(),
        };
        while no_pointers > 0 {
            elem_ty = cx.type_ptr_to(elem_ty);
            no_pointers -= 1;
        }
        cx.type_vector(elem_ty, vec_len)
    }

    if name == sym::simd_gather {
        // simd_gather(values: <N x T>, pointers: <N x *_ T>,
        //             mask: <N x i{M}>) -> <N x T>
        // * N: number of elements in the input vectors
        // * T: type of the element to load
        // * M: any integer width is supported, will be truncated to i1

        // All types must be simd vector types
        require_simd!(in_ty, "first");
        require_simd!(arg_tys[1], "second");
        require_simd!(arg_tys[2], "third");
        require_simd!(ret_ty, "return");

        // Of the same length:
        let (out_len, _) = arg_tys[1].simd_size_and_type(bx.tcx());
        let (out_len2, _) = arg_tys[2].simd_size_and_type(bx.tcx());
        require!(
            in_len == out_len,
            "expected {} argument with length {} (same as input type `{}`), \
             found `{}` with length {}",
            "second",
            in_len,
            in_ty,
            arg_tys[1],
            out_len
        );
        require!(
            in_len == out_len2,
            "expected {} argument with length {} (same as input type `{}`), \
             found `{}` with length {}",
            "third",
            in_len,
            in_ty,
            arg_tys[2],
            out_len2
        );

        // The return type must match the first argument type
        require!(ret_ty == in_ty, "expected return type `{}`, found `{}`", in_ty, ret_ty);

        // This counts how many pointers
        fn ptr_count(t: Ty<'_>) -> usize {
            match t.kind() {
                ty::RawPtr(p) => 1 + ptr_count(p.ty),
                _ => 0,
            }
        }

        // Non-ptr type
        fn non_ptr(t: Ty<'_>) -> Ty<'_> {
            match t.kind() {
                ty::RawPtr(p) => non_ptr(p.ty),
                _ => t,
            }
        }

        // The second argument must be a simd vector with an element type that's a pointer
        // to the element type of the first argument
        let (_, element_ty0) = arg_tys[0].simd_size_and_type(bx.tcx());
        let (_, element_ty1) = arg_tys[1].simd_size_and_type(bx.tcx());
        let (pointer_count, underlying_ty) = match element_ty1.kind() {
            ty::RawPtr(p) if p.ty == in_elem => (ptr_count(element_ty1), non_ptr(element_ty1)),
            _ => {
                require!(
                    false,
                    "expected element type `{}` of second argument `{}` \
                        to be a pointer to the element type `{}` of the first \
                        argument `{}`, found `{}` != `*_ {}`",
                    element_ty1,
                    arg_tys[1],
                    in_elem,
                    in_ty,
                    element_ty1,
                    in_elem
                );
                unreachable!();
            }
        };
        assert!(pointer_count > 0);
        assert_eq!(pointer_count - 1, ptr_count(element_ty0));
        assert_eq!(underlying_ty, non_ptr(element_ty0));

        // The element type of the third argument must be a signed integer type of any width:
        let (_, element_ty2) = arg_tys[2].simd_size_and_type(bx.tcx());
        match element_ty2.kind() {
            ty::Int(_) => (),
            _ => {
                require!(
                    false,
                    "expected element type `{}` of third argument `{}` \
                                 to be a signed integer type",
                    element_ty2,
                    arg_tys[2]
                );
            }
        }

        // Alignment of T, must be a constant integer value:
        let alignment_ty = bx.type_i32();
        let alignment = bx.const_i32(bx.align_of(in_elem).bytes() as i32);

        // Truncate the mask vector to a vector of i1s:
        let (mask, mask_ty) = {
            let i1 = bx.type_i1();
            let i1xn = bx.type_vector(i1, in_len);
            (bx.trunc(args[2].immediate(), i1xn), i1xn)
        };

        // Type of the vector of pointers:
        let llvm_pointer_vec_ty = llvm_vector_ty(bx, underlying_ty, in_len, pointer_count);
        let llvm_pointer_vec_str = llvm_vector_str(underlying_ty, in_len, pointer_count, bx);

        // Type of the vector of elements:
        let llvm_elem_vec_ty = llvm_vector_ty(bx, underlying_ty, in_len, pointer_count - 1);
        let llvm_elem_vec_str = llvm_vector_str(underlying_ty, in_len, pointer_count - 1, bx);

        let llvm_intrinsic =
            format!("llvm.masked.gather.{}.{}", llvm_elem_vec_str, llvm_pointer_vec_str);
        let fn_ty = bx.type_func(
            &[llvm_pointer_vec_ty, alignment_ty, mask_ty, llvm_elem_vec_ty],
            llvm_elem_vec_ty,
        );
        let f = bx.declare_cfn(&llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
        let v = bx.call(
            fn_ty,
            None,
            f,
            &[args[1].immediate(), alignment, mask, args[0].immediate()],
            None,
        );
        return Ok(v);
    }

    if name == sym::simd_scatter {
        // simd_scatter(values: <N x T>, pointers: <N x *mut T>,
        //             mask: <N x i{M}>) -> ()
        // * N: number of elements in the input vectors
        // * T: type of the element to load
        // * M: any integer width is supported, will be truncated to i1

        // All types must be simd vector types
        require_simd!(in_ty, "first");
        require_simd!(arg_tys[1], "second");
        require_simd!(arg_tys[2], "third");

        // Of the same length:
        let (element_len1, _) = arg_tys[1].simd_size_and_type(bx.tcx());
        let (element_len2, _) = arg_tys[2].simd_size_and_type(bx.tcx());
        require!(
            in_len == element_len1,
            "expected {} argument with length {} (same as input type `{}`), \
            found `{}` with length {}",
            "second",
            in_len,
            in_ty,
            arg_tys[1],
            element_len1
        );
        require!(
            in_len == element_len2,
            "expected {} argument with length {} (same as input type `{}`), \
            found `{}` with length {}",
            "third",
            in_len,
            in_ty,
            arg_tys[2],
            element_len2
        );

        // This counts how many pointers
        fn ptr_count(t: Ty<'_>) -> usize {
            match t.kind() {
                ty::RawPtr(p) => 1 + ptr_count(p.ty),
                _ => 0,
            }
        }

        // Non-ptr type
        fn non_ptr(t: Ty<'_>) -> Ty<'_> {
            match t.kind() {
                ty::RawPtr(p) => non_ptr(p.ty),
                _ => t,
            }
        }

        // The second argument must be a simd vector with an element type that's a pointer
        // to the element type of the first argument
        let (_, element_ty0) = arg_tys[0].simd_size_and_type(bx.tcx());
        let (_, element_ty1) = arg_tys[1].simd_size_and_type(bx.tcx());
        let (_, element_ty2) = arg_tys[2].simd_size_and_type(bx.tcx());
        let (pointer_count, underlying_ty) = match element_ty1.kind() {
            ty::RawPtr(p) if p.ty == in_elem && p.mutbl == hir::Mutability::Mut => {
                (ptr_count(element_ty1), non_ptr(element_ty1))
            }
            _ => {
                require!(
                    false,
                    "expected element type `{}` of second argument `{}` \
                        to be a pointer to the element type `{}` of the first \
                        argument `{}`, found `{}` != `*mut {}`",
                    element_ty1,
                    arg_tys[1],
                    in_elem,
                    in_ty,
                    element_ty1,
                    in_elem
                );
                unreachable!();
            }
        };
        assert!(pointer_count > 0);
        assert_eq!(pointer_count - 1, ptr_count(element_ty0));
        assert_eq!(underlying_ty, non_ptr(element_ty0));

        // The element type of the third argument must be a signed integer type of any width:
        match element_ty2.kind() {
            ty::Int(_) => (),
            _ => {
                require!(
                    false,
                    "expected element type `{}` of third argument `{}` \
                         be a signed integer type",
                    element_ty2,
                    arg_tys[2]
                );
            }
        }

        // Alignment of T, must be a constant integer value:
        let alignment_ty = bx.type_i32();
        let alignment = bx.const_i32(bx.align_of(in_elem).bytes() as i32);

        // Truncate the mask vector to a vector of i1s:
        let (mask, mask_ty) = {
            let i1 = bx.type_i1();
            let i1xn = bx.type_vector(i1, in_len);
            (bx.trunc(args[2].immediate(), i1xn), i1xn)
        };

        let ret_t = bx.type_void();

        // Type of the vector of pointers:
        let llvm_pointer_vec_ty = llvm_vector_ty(bx, underlying_ty, in_len, pointer_count);
        let llvm_pointer_vec_str = llvm_vector_str(underlying_ty, in_len, pointer_count, bx);

        // Type of the vector of elements:
        let llvm_elem_vec_ty = llvm_vector_ty(bx, underlying_ty, in_len, pointer_count - 1);
        let llvm_elem_vec_str = llvm_vector_str(underlying_ty, in_len, pointer_count - 1, bx);

        let llvm_intrinsic =
            format!("llvm.masked.scatter.{}.{}", llvm_elem_vec_str, llvm_pointer_vec_str);
        let fn_ty =
            bx.type_func(&[llvm_elem_vec_ty, llvm_pointer_vec_ty, alignment_ty, mask_ty], ret_t);
        let f = bx.declare_cfn(&llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
        let v = bx.call(
            fn_ty,
            None,
            f,
            &[args[0].immediate(), args[1].immediate(), alignment, mask],
            None,
        );
        return Ok(v);
    }

    macro_rules! arith_red {
        ($name:ident : $integer_reduce:ident, $float_reduce:ident, $ordered:expr, $op:ident,
         $identity:expr) => {
            if name == sym::$name {
                require!(
                    ret_ty == in_elem,
                    "expected return type `{}` (element of input `{}`), found `{}`",
                    in_elem,
                    in_ty,
                    ret_ty
                );
                return match in_elem.kind() {
                    ty::Int(_) | ty::Uint(_) => {
                        let r = bx.$integer_reduce(args[0].immediate());
                        if $ordered {
                            // if overflow occurs, the result is the
                            // mathematical result modulo 2^n:
                            Ok(bx.$op(args[1].immediate(), r))
                        } else {
                            Ok(bx.$integer_reduce(args[0].immediate()))
                        }
                    }
                    ty::Float(f) => {
                        let acc = if $ordered {
                            // ordered arithmetic reductions take an accumulator
                            args[1].immediate()
                        } else {
                            // unordered arithmetic reductions use the identity accumulator
                            match f.bit_width() {
                                32 => bx.const_real(bx.type_f32(), $identity),
                                64 => bx.const_real(bx.type_f64(), $identity),
                                v => return_error!(
                                    r#"
unsupported {} from `{}` with element `{}` of size `{}` to `{}`"#,
                                    sym::$name,
                                    in_ty,
                                    in_elem,
                                    v,
                                    ret_ty
                                ),
                            }
                        };
                        Ok(bx.$float_reduce(acc, args[0].immediate()))
                    }
                    _ => return_error!(
                        "unsupported {} from `{}` with element `{}` to `{}`",
                        sym::$name,
                        in_ty,
                        in_elem,
                        ret_ty
                    ),
                };
            }
        };
    }

    arith_red!(simd_reduce_add_ordered: vector_reduce_add, vector_reduce_fadd, true, add, 0.0);
    arith_red!(simd_reduce_mul_ordered: vector_reduce_mul, vector_reduce_fmul, true, mul, 1.0);
    arith_red!(
        simd_reduce_add_unordered: vector_reduce_add,
        vector_reduce_fadd_fast,
        false,
        add,
        0.0
    );
    arith_red!(
        simd_reduce_mul_unordered: vector_reduce_mul,
        vector_reduce_fmul_fast,
        false,
        mul,
        1.0
    );

    macro_rules! minmax_red {
        ($name:ident: $int_red:ident, $float_red:ident) => {
            if name == sym::$name {
                require!(
                    ret_ty == in_elem,
                    "expected return type `{}` (element of input `{}`), found `{}`",
                    in_elem,
                    in_ty,
                    ret_ty
                );
                return match in_elem.kind() {
                    ty::Int(_i) => Ok(bx.$int_red(args[0].immediate(), true)),
                    ty::Uint(_u) => Ok(bx.$int_red(args[0].immediate(), false)),
                    ty::Float(_f) => Ok(bx.$float_red(args[0].immediate())),
                    _ => return_error!(
                        "unsupported {} from `{}` with element `{}` to `{}`",
                        sym::$name,
                        in_ty,
                        in_elem,
                        ret_ty
                    ),
                };
            }
        };
    }

    minmax_red!(simd_reduce_min: vector_reduce_min, vector_reduce_fmin);
    minmax_red!(simd_reduce_max: vector_reduce_max, vector_reduce_fmax);

    minmax_red!(simd_reduce_min_nanless: vector_reduce_min, vector_reduce_fmin_fast);
    minmax_red!(simd_reduce_max_nanless: vector_reduce_max, vector_reduce_fmax_fast);

    macro_rules! bitwise_red {
        ($name:ident : $red:ident, $boolean:expr) => {
            if name == sym::$name {
                let input = if !$boolean {
                    require!(
                        ret_ty == in_elem,
                        "expected return type `{}` (element of input `{}`), found `{}`",
                        in_elem,
                        in_ty,
                        ret_ty
                    );
                    args[0].immediate()
                } else {
                    match in_elem.kind() {
                        ty::Int(_) | ty::Uint(_) => {}
                        _ => return_error!(
                            "unsupported {} from `{}` with element `{}` to `{}`",
                            sym::$name,
                            in_ty,
                            in_elem,
                            ret_ty
                        ),
                    }

                    // boolean reductions operate on vectors of i1s:
                    let i1 = bx.type_i1();
                    let i1xn = bx.type_vector(i1, in_len as u64);
                    bx.trunc(args[0].immediate(), i1xn)
                };
                return match in_elem.kind() {
                    ty::Int(_) | ty::Uint(_) => {
                        let r = bx.$red(input);
                        Ok(if !$boolean { r } else { bx.zext(r, bx.type_bool()) })
                    }
                    _ => return_error!(
                        "unsupported {} from `{}` with element `{}` to `{}`",
                        sym::$name,
                        in_ty,
                        in_elem,
                        ret_ty
                    ),
                };
            }
        };
    }

    bitwise_red!(simd_reduce_and: vector_reduce_and, false);
    bitwise_red!(simd_reduce_or: vector_reduce_or, false);
    bitwise_red!(simd_reduce_xor: vector_reduce_xor, false);
    bitwise_red!(simd_reduce_all: vector_reduce_and, true);
    bitwise_red!(simd_reduce_any: vector_reduce_or, true);

    if name == sym::simd_cast_ptr {
        require_simd!(ret_ty, "return");
        let (out_len, out_elem) = ret_ty.simd_size_and_type(bx.tcx());
        require!(
            in_len == out_len,
            "expected return type with length {} (same as input type `{}`), \
                  found `{}` with length {}",
            in_len,
            in_ty,
            ret_ty,
            out_len
        );

        match in_elem.kind() {
            ty::RawPtr(p) => {
                let (metadata, check_sized) = p.ty.ptr_metadata_ty(bx.tcx, |ty| {
                    bx.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), ty)
                });
                assert!(!check_sized); // we are in codegen, so we shouldn't see these types
                require!(metadata.is_unit(), "cannot cast fat pointer `{}`", in_elem)
            }
            _ => return_error!("expected pointer, got `{}`", in_elem),
        }
        match out_elem.kind() {
            ty::RawPtr(p) => {
                let (metadata, check_sized) = p.ty.ptr_metadata_ty(bx.tcx, |ty| {
                    bx.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), ty)
                });
                assert!(!check_sized); // we are in codegen, so we shouldn't see these types
                require!(metadata.is_unit(), "cannot cast to fat pointer `{}`", out_elem)
            }
            _ => return_error!("expected pointer, got `{}`", out_elem),
        }

        if in_elem == out_elem {
            return Ok(args[0].immediate());
        } else {
            return Ok(bx.pointercast(args[0].immediate(), llret_ty));
        }
    }

    if name == sym::simd_expose_addr {
        require_simd!(ret_ty, "return");
        let (out_len, out_elem) = ret_ty.simd_size_and_type(bx.tcx());
        require!(
            in_len == out_len,
            "expected return type with length {} (same as input type `{}`), \
                  found `{}` with length {}",
            in_len,
            in_ty,
            ret_ty,
            out_len
        );

        match in_elem.kind() {
            ty::RawPtr(_) => {}
            _ => return_error!("expected pointer, got `{}`", in_elem),
        }
        match out_elem.kind() {
            ty::Uint(ty::UintTy::Usize) => {}
            _ => return_error!("expected `usize`, got `{}`", out_elem),
        }

        return Ok(bx.ptrtoint(args[0].immediate(), llret_ty));
    }

    if name == sym::simd_from_exposed_addr {
        require_simd!(ret_ty, "return");
        let (out_len, out_elem) = ret_ty.simd_size_and_type(bx.tcx());
        require!(
            in_len == out_len,
            "expected return type with length {} (same as input type `{}`), \
                  found `{}` with length {}",
            in_len,
            in_ty,
            ret_ty,
            out_len
        );

        match in_elem.kind() {
            ty::Uint(ty::UintTy::Usize) => {}
            _ => return_error!("expected `usize`, got `{}`", in_elem),
        }
        match out_elem.kind() {
            ty::RawPtr(_) => {}
            _ => return_error!("expected pointer, got `{}`", out_elem),
        }

        return Ok(bx.inttoptr(args[0].immediate(), llret_ty));
    }

    if name == sym::simd_cast || name == sym::simd_as {
        require_simd!(ret_ty, "return");
        let (out_len, out_elem) = ret_ty.simd_size_and_type(bx.tcx());
        require!(
            in_len == out_len,
            "expected return type with length {} (same as input type `{}`), \
                  found `{}` with length {}",
            in_len,
            in_ty,
            ret_ty,
            out_len
        );
        // casting cares about nominal type, not just structural type
        if in_elem == out_elem {
            return Ok(args[0].immediate());
        }

        enum Style {
            Float,
            Int(/* is signed? */ bool),
            Unsupported,
        }

        let (in_style, in_width) = match in_elem.kind() {
            // vectors of pointer-sized integers should've been
            // disallowed before here, so this unwrap is safe.
            ty::Int(i) => (
                Style::Int(true),
                i.normalize(bx.tcx().sess.target.pointer_width).bit_width().unwrap(),
            ),
            ty::Uint(u) => (
                Style::Int(false),
                u.normalize(bx.tcx().sess.target.pointer_width).bit_width().unwrap(),
            ),
            ty::Float(f) => (Style::Float, f.bit_width()),
            _ => (Style::Unsupported, 0),
        };
        let (out_style, out_width) = match out_elem.kind() {
            ty::Int(i) => (
                Style::Int(true),
                i.normalize(bx.tcx().sess.target.pointer_width).bit_width().unwrap(),
            ),
            ty::Uint(u) => (
                Style::Int(false),
                u.normalize(bx.tcx().sess.target.pointer_width).bit_width().unwrap(),
            ),
            ty::Float(f) => (Style::Float, f.bit_width()),
            _ => (Style::Unsupported, 0),
        };

        match (in_style, out_style) {
            (Style::Int(in_is_signed), Style::Int(_)) => {
                return Ok(match in_width.cmp(&out_width) {
                    Ordering::Greater => bx.trunc(args[0].immediate(), llret_ty),
                    Ordering::Equal => args[0].immediate(),
                    Ordering::Less => {
                        if in_is_signed {
                            bx.sext(args[0].immediate(), llret_ty)
                        } else {
                            bx.zext(args[0].immediate(), llret_ty)
                        }
                    }
                });
            }
            (Style::Int(in_is_signed), Style::Float) => {
                return Ok(if in_is_signed {
                    bx.sitofp(args[0].immediate(), llret_ty)
                } else {
                    bx.uitofp(args[0].immediate(), llret_ty)
                });
            }
            (Style::Float, Style::Int(out_is_signed)) => {
                return Ok(match (out_is_signed, name == sym::simd_as) {
                    (false, false) => bx.fptoui(args[0].immediate(), llret_ty),
                    (true, false) => bx.fptosi(args[0].immediate(), llret_ty),
                    (_, true) => bx.cast_float_to_int(out_is_signed, args[0].immediate(), llret_ty),
                });
            }
            (Style::Float, Style::Float) => {
                return Ok(match in_width.cmp(&out_width) {
                    Ordering::Greater => bx.fptrunc(args[0].immediate(), llret_ty),
                    Ordering::Equal => args[0].immediate(),
                    Ordering::Less => bx.fpext(args[0].immediate(), llret_ty),
                });
            }
            _ => { /* Unsupported. Fallthrough. */ }
        }
        require!(
            false,
            "unsupported cast from `{}` with element `{}` to `{}` with element `{}`",
            in_ty,
            in_elem,
            ret_ty,
            out_elem
        );
    }
    macro_rules! arith_binary {
        ($($name: ident: $($($p: ident),* => $call: ident),*;)*) => {
            $(if name == sym::$name {
                match in_elem.kind() {
                    $($(ty::$p(_))|* => {
                        return Ok(bx.$call(args[0].immediate(), args[1].immediate()))
                    })*
                    _ => {},
                }
                require!(false,
                         "unsupported operation on `{}` with element `{}`",
                         in_ty,
                         in_elem)
            })*
        }
    }
    arith_binary! {
        simd_add: Uint, Int => add, Float => fadd;
        simd_sub: Uint, Int => sub, Float => fsub;
        simd_mul: Uint, Int => mul, Float => fmul;
        simd_div: Uint => udiv, Int => sdiv, Float => fdiv;
        simd_rem: Uint => urem, Int => srem, Float => frem;
        simd_shl: Uint, Int => shl;
        simd_shr: Uint => lshr, Int => ashr;
        simd_and: Uint, Int => and;
        simd_or: Uint, Int => or;
        simd_xor: Uint, Int => xor;
        simd_fmax: Float => maxnum;
        simd_fmin: Float => minnum;

    }
    macro_rules! arith_unary {
        ($($name: ident: $($($p: ident),* => $call: ident),*;)*) => {
            $(if name == sym::$name {
                match in_elem.kind() {
                    $($(ty::$p(_))|* => {
                        return Ok(bx.$call(args[0].immediate()))
                    })*
                    _ => {},
                }
                require!(false,
                         "unsupported operation on `{}` with element `{}`",
                         in_ty,
                         in_elem)
            })*
        }
    }
    arith_unary! {
        simd_neg: Int => neg, Float => fneg;
    }

    if name == sym::simd_arith_offset {
        // This also checks that the first operand is a ptr type.
        let pointee = in_elem.builtin_deref(true).unwrap_or_else(|| {
            span_bug!(span, "must be called with a vector of pointer types as first argument")
        });
        let layout = bx.layout_of(pointee.ty);
        let ptrs = args[0].immediate();
        // The second argument must be a ptr-sized integer.
        // (We don't care about the signedness, this is wrapping anyway.)
        let (_offsets_len, offsets_elem) = arg_tys[1].simd_size_and_type(bx.tcx());
        if !matches!(offsets_elem.kind(), ty::Int(ty::IntTy::Isize) | ty::Uint(ty::UintTy::Usize)) {
            span_bug!(
                span,
                "must be called with a vector of pointer-sized integers as second argument"
            );
        }
        let offsets = args[1].immediate();

        return Ok(bx.gep(bx.backend_type(layout), ptrs, &[offsets]));
    }

    if name == sym::simd_saturating_add || name == sym::simd_saturating_sub {
        let lhs = args[0].immediate();
        let rhs = args[1].immediate();
        let is_add = name == sym::simd_saturating_add;
        let ptr_bits = bx.tcx().data_layout.pointer_size.bits() as _;
        let (signed, elem_width, elem_ty) = match *in_elem.kind() {
            ty::Int(i) => (true, i.bit_width().unwrap_or(ptr_bits), bx.cx.type_int_from_ty(i)),
            ty::Uint(i) => (false, i.bit_width().unwrap_or(ptr_bits), bx.cx.type_uint_from_ty(i)),
            _ => {
                return_error!(
                    "expected element type `{}` of vector type `{}` \
                     to be a signed or unsigned integer type",
                    arg_tys[0].simd_size_and_type(bx.tcx()).1,
                    arg_tys[0]
                );
            }
        };
        let llvm_intrinsic = &format!(
            "llvm.{}{}.sat.v{}i{}",
            if signed { 's' } else { 'u' },
            if is_add { "add" } else { "sub" },
            in_len,
            elem_width
        );
        let vec_ty = bx.cx.type_vector(elem_ty, in_len as u64);

        let fn_ty = bx.type_func(&[vec_ty, vec_ty], vec_ty);
        let f = bx.declare_cfn(llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
        let v = bx.call(fn_ty, None, f, &[lhs, rhs], None);
        return Ok(v);
    }

    span_bug!(span, "unknown SIMD intrinsic");
}

// Returns the width of an int Ty, and if it's signed or not
// Returns None if the type is not an integer
// FIXME: there’s multiple of this functions, investigate using some of the already existing
// stuffs.
fn int_type_width_signed(ty: Ty<'_>, cx: &CodegenCx<'_, '_>) -> Option<(u64, bool)> {
    match ty.kind() {
        ty::Int(t) => {
            Some((t.bit_width().unwrap_or(u64::from(cx.tcx.sess.target.pointer_width)), true))
        }
        ty::Uint(t) => {
            Some((t.bit_width().unwrap_or(u64::from(cx.tcx.sess.target.pointer_width)), false))
        }
        _ => None,
    }
}