Impressum writer.rs   Interaktion und
Portierbarkeitunbekannt

use super::{
    block::DebugInfoInner,
    helpers::{contains_builtin, global_needs_wrapper, map_storage_class},
    Block, BlockContext, CachedConstant, CachedExpressions, DebugInfo, EntryPointContext, Error,
    Function, FunctionArgument, GlobalVariable, IdGenerator, Instruction, LocalType, LocalVariable,
    LogicalLayout, LookupFunctionType, LookupType, NumericType, Options, PhysicalLayout,
    PipelineOptions, ResultMember, Writer, WriterFlags, BITS_PER_BYTE,
};
use crate::{
    arena::{Handle, HandleVec, UniqueArena},
    back::spv::BindingInfo,
    proc::{Alignment, TypeResolution},
    valid::{FunctionInfo, ModuleInfo},
};
use spirv::Word;
use std::collections::hash_map::Entry;

struct FunctionInterface<'a> {
    varying_ids: &'a mut Vec<Word>,
    stage: crate::ShaderStage,
}

impl Function {
    fn to_words(&self, sink: &mut impl Extend<Word>) {
        self.signature.as_ref().unwrap().to_words(sink);
        for argument in self.parameters.iter() {
            argument.instruction.to_words(sink);
        }
        for (index, block) in self.blocks.iter().enumerate() {
            Instruction::label(block.label_id).to_words(sink);
            if index == 0 {
                for local_var in self.variables.values() {
                    local_var.instruction.to_words(sink);
                }
                for internal_var in self.spilled_composites.values() {
                    internal_var.instruction.to_words(sink);
                }
            }
            for instruction in block.body.iter() {
                instruction.to_words(sink);
            }
        }
    }
}

impl Writer {
    pub fn new(options: &Options) -> Result<Self, Error> {
        let (major, minor) = options.lang_version;
        if major != 1 {
            return Err(Error::UnsupportedVersion(major, minor));
        }
        let raw_version = ((major as u32) << 16) | ((minor as u32) << 8);

        let mut capabilities_used = crate::FastIndexSet::default();
        capabilities_used.insert(spirv::Capability::Shader);

        let mut id_gen = IdGenerator::default();
        let gl450_ext_inst_id = id_gen.next();
        let void_type = id_gen.next();

        Ok(Writer {
            physical_layout: PhysicalLayout::new(raw_version),
            logical_layout: LogicalLayout::default(),
            id_gen,
            capabilities_available: options.capabilities.clone(),
            capabilities_used,
            extensions_used: crate::FastIndexSet::default(),
            debugs: vec![],
            annotations: vec![],
            flags: options.flags,
            bounds_check_policies: options.bounds_check_policies,
            zero_initialize_workgroup_memory: options.zero_initialize_workgroup_memory,
            void_type,
            lookup_type: crate::FastHashMap::default(),
            lookup_function: crate::FastHashMap::default(),
            lookup_function_type: crate::FastHashMap::default(),
            constant_ids: HandleVec::new(),
            cached_constants: crate::FastHashMap::default(),
            global_variables: HandleVec::new(),
            binding_map: options.binding_map.clone(),
            saved_cached: CachedExpressions::default(),
            gl450_ext_inst_id,
            temp_list: Vec::new(),
        })
    }

    /// Reset `Writer` to its initial state, retaining any allocations.
    ///
    /// Why not just implement `Recyclable` for `Writer`? By design,
    /// `Recyclable::recycle` requires ownership of the value, not just
    /// `&mut`; see the trait documentation. But we need to use this method
    /// from functions like `Writer::write`, which only have `&mut Writer`.
    /// Workarounds include unsafe code (`std::ptr::read`, then `write`, ugh)
    /// or something like a `Default` impl that returns an oddly-initialized
    /// `Writer`, which is worse.
    fn reset(&mut self) {
        use super::recyclable::Recyclable;
        use std::mem::take;

        let mut id_gen = IdGenerator::default();
        let gl450_ext_inst_id = id_gen.next();
        let void_type = id_gen.next();

        // Every field of the old writer that is not determined by the `Options`
        // passed to `Writer::new` should be reset somehow.
        let fresh = Writer {
            // Copied from the old Writer:
            flags: self.flags,
            bounds_check_policies: self.bounds_check_policies,
            zero_initialize_workgroup_memory: self.zero_initialize_workgroup_memory,
            capabilities_available: take(&mut self.capabilities_available),
            binding_map: take(&mut self.binding_map),

            // Initialized afresh:
            id_gen,
            void_type,
            gl450_ext_inst_id,

            // Recycled:
            capabilities_used: take(&mut self.capabilities_used).recycle(),
            extensions_used: take(&mut self.extensions_used).recycle(),
            physical_layout: self.physical_layout.clone().recycle(),
            logical_layout: take(&mut self.logical_layout).recycle(),
            debugs: take(&mut self.debugs).recycle(),
            annotations: take(&mut self.annotations).recycle(),
            lookup_type: take(&mut self.lookup_type).recycle(),
            lookup_function: take(&mut self.lookup_function).recycle(),
            lookup_function_type: take(&mut self.lookup_function_type).recycle(),
            constant_ids: take(&mut self.constant_ids).recycle(),
            cached_constants: take(&mut self.cached_constants).recycle(),
            global_variables: take(&mut self.global_variables).recycle(),
            saved_cached: take(&mut self.saved_cached).recycle(),
            temp_list: take(&mut self.temp_list).recycle(),
        };

        *self = fresh;

        self.capabilities_used.insert(spirv::Capability::Shader);
    }

    /// Indicate that the code requires any one of the listed capabilities.
    ///
    /// If nothing in `capabilities` appears in the available capabilities
    /// specified in the [`Options`] from which this `Writer` was created,
    /// return an error. The `what` string is used in the error message to
    /// explain what provoked the requirement. (If no available capabilities were
    /// given, assume everything is available.)
    ///
    /// The first acceptable capability will be added to this `Writer`'s
    /// [`capabilities_used`] table, and an `OpCapability` emitted for it in the
    /// result. For this reason, more specific capabilities should be listed
    /// before more general.
    ///
    /// [`capabilities_used`]: Writer::capabilities_used
    pub(super) fn require_any(
        &mut self,
        what: &'static str,
        capabilities: &[spirv::Capability],
    ) -> Result<(), Error> {
        match *capabilities {
            [] => Ok(()),
            [first, ..] => {
                // Find the first acceptable capability, or return an error if
                // there is none.
                let selected = match self.capabilities_available {
                    None => first,
                    Some(ref available) => {
                        match capabilities.iter().find(|cap| available.contains(cap)) {
                            Some(&cap) => cap,
                            None => {
                                return Err(Error::MissingCapabilities(what, capabilities.to_vec()))
                            }
                        }
                    }
                };
                self.capabilities_used.insert(selected);
                Ok(())
            }
        }
    }

    /// Indicate that the code uses the given extension.
    pub(super) fn use_extension(&mut self, extension: &'static str) {
        self.extensions_used.insert(extension);
    }

    pub(super) fn get_type_id(&mut self, lookup_ty: LookupType) -> Word {
        match self.lookup_type.entry(lookup_ty) {
            Entry::Occupied(e) => *e.get(),
            Entry::Vacant(e) => {
                let local = match lookup_ty {
                    LookupType::Handle(_handle) => unreachable!("Handles are populated at start"),
                    LookupType::Local(local) => local,
                };

                let id = self.id_gen.next();
                e.insert(id);
                self.write_type_declaration_local(id, local);
                id
            }
        }
    }

    pub(super) fn get_expression_lookup_type(&mut self, tr: &TypeResolution) -> LookupType {
        match *tr {
            TypeResolution::Handle(ty_handle) => LookupType::Handle(ty_handle),
            TypeResolution::Value(ref inner) => {
                LookupType::Local(LocalType::from_inner(inner).unwrap())
            }
        }
    }

    pub(super) fn get_expression_type_id(&mut self, tr: &TypeResolution) -> Word {
        let lookup_ty = self.get_expression_lookup_type(tr);
        self.get_type_id(lookup_ty)
    }

    pub(super) fn get_pointer_id(
        &mut self,
        handle: Handle<crate::Type>,
        class: spirv::StorageClass,
    ) -> Word {
        self.get_type_id(LookupType::Local(LocalType::Pointer {
            base: handle,
            class,
        }))
    }

    /// Return a SPIR-V type for a pointer to `resolution`.
    ///
    /// The given `resolution` must be one that we can represent
    /// either as a `LocalType::Pointer` or `LocalType::LocalPointer`.
    pub(super) fn get_resolution_pointer_id(
        &mut self,
        resolution: &TypeResolution,
        class: spirv::StorageClass,
    ) -> Word {
        match *resolution {
            TypeResolution::Handle(handle) => self.get_pointer_id(handle, class),
            TypeResolution::Value(ref inner) => {
                let base = NumericType::from_inner(inner).unwrap();
                self.get_type_id(LookupType::Local(LocalType::LocalPointer { base, class }))
            }
        }
    }

    pub(super) fn get_uint_type_id(&mut self) -> Word {
        let local_type = LocalType::Numeric(NumericType::Scalar(crate::Scalar::U32));
        self.get_type_id(local_type.into())
    }

    pub(super) fn get_float_type_id(&mut self) -> Word {
        let local_type = LocalType::Numeric(NumericType::Scalar(crate::Scalar::F32));
        self.get_type_id(local_type.into())
    }

    pub(super) fn get_uint3_type_id(&mut self) -> Word {
        let local_type = LocalType::Numeric(NumericType::Vector {
            size: crate::VectorSize::Tri,
            scalar: crate::Scalar::U32,
        });
        self.get_type_id(local_type.into())
    }

    pub(super) fn get_float_pointer_type_id(&mut self, class: spirv::StorageClass) -> Word {
        let local_type = LocalType::LocalPointer {
            base: NumericType::Scalar(crate::Scalar::F32),
            class,
        };
        self.get_type_id(local_type.into())
    }

    pub(super) fn get_uint3_pointer_type_id(&mut self, class: spirv::StorageClass) -> Word {
        let local_type = LocalType::LocalPointer {
            base: NumericType::Vector {
                size: crate::VectorSize::Tri,
                scalar: crate::Scalar::U32,
            },
            class,
        };
        self.get_type_id(local_type.into())
    }

    pub(super) fn get_bool_type_id(&mut self) -> Word {
        let local_type = LocalType::Numeric(NumericType::Scalar(crate::Scalar::BOOL));
        self.get_type_id(local_type.into())
    }

    pub(super) fn get_bool3_type_id(&mut self) -> Word {
        let local_type = LocalType::Numeric(NumericType::Vector {
            size: crate::VectorSize::Tri,
            scalar: crate::Scalar::BOOL,
        });
        self.get_type_id(local_type.into())
    }

    pub(super) fn decorate(&mut self, id: Word, decoration: spirv::Decoration, operands: &[Word])&nbsp;{
        self.annotations
            .push(Instruction::decorate(id, decoration, operands));
    }

    fn write_function(
        &mut self,
        ir_function: &crate::Function,
        info: &FunctionInfo,
        ir_module: &crate::Module,
        mut interface: Option<FunctionInterface>,
        debug_info: &Option<DebugInfoInner>,
    ) -> Result<Word, Error> {
        log::trace!("Generating code for {:?}", ir_function.name);
        let mut function = Function::default();

        let prelude_id = self.id_gen.next();
        let mut prelude = Block::new(prelude_id);
        let mut ep_context = EntryPointContext {
            argument_ids: Vec::new(),
            results: Vec::new(),
        };

        let mut local_invocation_id = None;

        let mut parameter_type_ids = Vec::with_capacity(ir_function.arguments.len());
        for argument in ir_function.arguments.iter() {
            let class = spirv::StorageClass::Input;
            let handle_ty = ir_module.types[argument.ty].inner.is_handle();
            let argument_type_id = match handle_ty {
                true => self.get_pointer_id(argument.ty, spirv::StorageClass::UniformConstant),
                false => self.get_type_id(LookupType::Handle(argument.ty)),
            };

            if let Some(ref mut iface) = interface {
                let id = if let Some(ref binding) = argument.binding {
                    let name = argument.name.as_deref();

                    let varying_id = self.write_varying(
                        ir_module,
                        iface.stage,
                        class,
                        name,
                        argument.ty,
                        binding,
                    )?;
                    iface.varying_ids.push(varying_id);
                    let id = self.id_gen.next();
                    prelude
                        .body
                        .push(Instruction::load(argument_type_id, id, varying_id, None));

                    if binding == &crate::Binding::BuiltIn(crate::BuiltIn::LocalInvocationId) {
                        local_invocation_id = Some(id);
                    }

                    id
                } else if let crate::TypeInner::Struct { ref members, .. } =
                    ir_module.types[argument.ty].inner
                {
                    let struct_id = self.id_gen.next();
                    let mut constituent_ids = Vec::with_capacity(members.len());
                    for member in members {
                        let type_id = self.get_type_id(LookupType::Handle(member.ty));
                        let name = member.name.as_deref();
                        let binding = member.binding.as_ref().unwrap();
                        let varying_id = self.write_varying(
                            ir_module,
                            iface.stage,
                            class,
                            name,
                            member.ty,
                            binding,
                        )?;
                        iface.varying_ids.push(varying_id);
                        let id = self.id_gen.next();
                        prelude
                            .body
                            .push(Instruction::load(type_id, id, varying_id, None));
                        constituent_ids.push(id);

                        if binding == &crate::Binding::BuiltIn(crate::BuiltIn::GlobalInvocationId) {
                            local_invocation_id = Some(id);
                        }
                    }
                    prelude.body.push(Instruction::composite_construct(
                        argument_type_id,
                        struct_id,
                        &constituent_ids,
                    ));
                    struct_id
                } else {
                    unreachable!("Missing argument binding on an entry point");
                };
                ep_context.argument_ids.push(id);
            } else {
                let argument_id = self.id_gen.next();
                let instruction = Instruction::function_parameter(argument_type_id, argument_id);
                if self.flags.contains(WriterFlags::DEBUG) {
                    if let Some(ref name) = argument.name {
                        self.debugs.push(Instruction::name(argument_id, name));
                    }
                }
                function.parameters.push(FunctionArgument {
                    instruction,
                    handle_id: if handle_ty {
                        let id = self.id_gen.next();
                        prelude.body.push(Instruction::load(
                            self.get_type_id(LookupType::Handle(argument.ty)),
                            id,
                            argument_id,
                            None,
                        ));
                        id
                    } else {
                        0
                    },
                });
                parameter_type_ids.push(argument_type_id);
            };
        }

        let return_type_id = match ir_function.result {
            Some(ref result) => {
                if let Some(ref mut iface) = interface {
                    let mut has_point_size = false;
                    let class = spirv::StorageClass::Output;
                    if let Some(ref binding) = result.binding {
                        has_point_size |=
                            *binding == crate::Binding::BuiltIn(crate::BuiltIn::PointSize);
                        let type_id = self.get_type_id(LookupType::Handle(result.ty));
                        let varying_id = self.write_varying(
                            ir_module,
                            iface.stage,
                            class,
                            None,
                            result.ty,
                            binding,
                        )?;
                        iface.varying_ids.push(varying_id);
                        ep_context.results.push(ResultMember {
                            id: varying_id,
                            type_id,
                            built_in: binding.to_built_in(),
                        });
                    } else if let crate::TypeInner::Struct { ref members, .. } =
                        ir_module.types[result.ty].inner
                    {
                        for member in members {
                            let type_id = self.get_type_id(LookupType::Handle(member.ty));
                            let name = member.name.as_deref();
                            let binding = member.binding.as_ref().unwrap();
                            has_point_size |=
                                *binding == crate::Binding::BuiltIn(crate::BuiltIn::PointSize);
                            let varying_id = self.write_varying(
                                ir_module,
                                iface.stage,
                                class,
                                name,
                                member.ty,
                                binding,
                            )?;
                            iface.varying_ids.push(varying_id);
                            ep_context.results.push(ResultMember {
                                id: varying_id,
                                type_id,
                                built_in: binding.to_built_in(),
                            });
                        }
                    } else {
                        unreachable!("Missing result binding on an entry point");
                    }

                    if self.flags.contains(WriterFlags::FORCE_POINT_SIZE)
                        && iface.stage == crate::ShaderStage::Vertex
                        && !has_point_size
                    {
                        // add point size artificially
                        let varying_id = self.id_gen.next();
                        let pointer_type_id = self.get_float_pointer_type_id(class);
                        Instruction::variable(pointer_type_id, varying_id, class, None)
                            .to_words(&mut self.logical_layout.declarations);
                        self.decorate(
                            varying_id,
                            spirv::Decoration::BuiltIn,
                            &[spirv::BuiltIn::PointSize as u32],
                        );
                        iface.varying_ids.push(varying_id);

                        let default_value_id = self.get_constant_scalar(crate::Literal::F32(1.0));
                        prelude
                            .body
                            .push(Instruction::store(varying_id, default_value_id, None));
                    }
                    self.void_type
                } else {
                    self.get_type_id(LookupType::Handle(result.ty))
                }
            }
            None => self.void_type,
        };

        let lookup_function_type = LookupFunctionType {
            parameter_type_ids,
            return_type_id,
        };

        let function_id = self.id_gen.next();
        if self.flags.contains(WriterFlags::DEBUG) {
            if let Some(ref name) = ir_function.name {
                self.debugs.push(Instruction::name(function_id, name));
            }
        }

        let function_type = self.get_function_type(lookup_function_type);
        function.signature = Some(Instruction::function(
            return_type_id,
            function_id,
            spirv::FunctionControl::empty(),
            function_type,
        ));

        if interface.is_some() {
            function.entry_point_context = Some(ep_context);
        }

        // fill up the `GlobalVariable::access_id`
        for gv in self.global_variables.iter_mut() {
            gv.reset_for_function();
        }
        for (handle, var) in ir_module.global_variables.iter() {
            if info[handle].is_empty() {
                continue;
            }

            let mut gv = self.global_variables[handle].clone();
            if let Some(ref mut iface) = interface {
                // Have to include global variables in the interface
                if self.physical_layout.version >= 0x10400 {
                    iface.varying_ids.push(gv.var_id);
                }
            }

            // Handle globals are pre-emitted and should be loaded automatically.
            //
            // Any that are binding arrays we skip as we cannot load the array, we must load the result after indexing.
            match ir_module.types[var.ty].inner {
                crate::TypeInner::BindingArray { .. } => {
                    gv.access_id = gv.var_id;
                }
                _ => {
                    if var.space == crate::AddressSpace::Handle {
                        let var_type_id = self.get_type_id(LookupType::Handle(var.ty));
                        let id = self.id_gen.next();
                        prelude
                            .body
                            .push(Instruction::load(var_type_id, id, gv.var_id, None));
                        gv.access_id = gv.var_id;
                        gv.handle_id = id;
                    } else if global_needs_wrapper(ir_module, var) {
                        let class = map_storage_class(var.space);
                        let pointer_type_id = self.get_pointer_id(var.ty, class);
                        let index_id = self.get_index_constant(0);
                        let id = self.id_gen.next();
                        prelude.body.push(Instruction::access_chain(
                            pointer_type_id,
                            id,
                            gv.var_id,
                            &[index_id],
                        ));
                        gv.access_id = id;
                    } else {
                        // by default, the variable ID is accessed as is
                        gv.access_id = gv.var_id;
                    };
                }
            }

            // work around borrow checking in the presence of `self.xxx()` calls
            self.global_variables[handle] = gv;
        }

        // Create a `BlockContext` for generating SPIR-V for the function's
        // body.
        let mut context = BlockContext {
            ir_module,
            ir_function,
            fun_info: info,
            function: &mut function,
            // Re-use the cached expression table from prior functions.
            cached: std::mem::take(&mut self.saved_cached),

            // Steal the Writer's temp list for a bit.
            temp_list: std::mem::take(&mut self.temp_list),
            writer: self,
            expression_constness: super::ExpressionConstnessTracker::from_arena(
                &ir_function.expressions,
            ),
        };

        // fill up the pre-emitted and const expressions
        context.cached.reset(ir_function.expressions.len());
        for (handle, expr) in ir_function.expressions.iter() {
            if (expr.needs_pre_emit() && !matches!(*expr, crate::Expression::LocalVariable(_)))
                || context.expression_constness.is_const(handle)
            {
                context.cache_expression_value(handle, &mut prelude)?;
            }
        }

        for (handle, variable) in ir_function.local_variables.iter() {
            let id = context.gen_id();

            if context.writer.flags.contains(WriterFlags::DEBUG) {
                if let Some(ref name) = variable.name {
                    context.writer.debugs.push(Instruction::name(id, name));
                }
            }

            let init_word = variable.init.map(|constant| context.cached[constant]);
            let pointer_type_id = context
                .writer
                .get_pointer_id(variable.ty, spirv::StorageClass::Function);
            let instruction = Instruction::variable(
                pointer_type_id,
                id,
                spirv::StorageClass::Function,
                init_word.or_else(|| match ir_module.types[variable.ty].inner {
                    crate::TypeInner::RayQuery => None,
                    _ => {
                        let type_id = context.get_type_id(LookupType::Handle(variable.ty));
                        Some(context.writer.write_constant_null(type_id))
                    }
                }),
            );
            context
                .function
                .variables
                .insert(handle, LocalVariable { id, instruction });
        }

        for (handle, expr) in ir_function.expressions.iter() {
            match *expr {
                crate::Expression::LocalVariable(_) => {
                    // Cache the `OpVariable` instruction we generated above as
                    // the value of this expression.
                    context.cache_expression_value(handle, &mut prelude)?;
                }
                crate::Expression::Access { base, .. }
                | crate::Expression::AccessIndex { base, .. } => {
                    // Count references to `base` by `Access` and `AccessIndex`
                    // instructions. See `access_uses` for details.
                    *context.function.access_uses.entry(base).or_insert(0) += 1;
                }
                _ => {}
            }
        }

        let next_id = context.gen_id();

        context
            .function
            .consume(prelude, Instruction::branch(next_id));

        let workgroup_vars_init_exit_block_id =
            match (context.writer.zero_initialize_workgroup_memory, interface) {
                (
                    super::ZeroInitializeWorkgroupMemoryMode::Polyfill,
                    Some(
                        ref mut interface @ FunctionInterface {
                            stage: crate::ShaderStage::Compute,
                            ..
                        },
                    ),
                ) => context.writer.generate_workgroup_vars_init_block(
                    next_id,
                    ir_module,
                    info,
                    local_invocation_id,
                    interface,
                    context.function,
                ),
                _ => None,
            };

        let main_id = if let Some(exit_id) = workgroup_vars_init_exit_block_id {
            exit_id
        } else {
            next_id
        };

        context.write_function_body(main_id, debug_info.as_ref())?;

        // Consume the `BlockContext`, ending its borrows and letting the
        // `Writer` steal back its cached expression table and temp_list.
        let BlockContext {
            cached, temp_list, ..
        } = context;
        self.saved_cached = cached;
        self.temp_list = temp_list;

        function.to_words(&mut self.logical_layout.function_definitions);
        Instruction::function_end().to_words(&mut self.logical_layout.function_definitions);

        Ok(function_id)
    }

    fn write_execution_mode(
        &mut self,
        function_id: Word,
        mode: spirv::ExecutionMode,
    ) -> Result<(), Error> {
        //self.check(mode.required_capabilities())?;
        Instruction::execution_mode(function_id, mode, &[])
            .to_words(&mut self.logical_layout.execution_modes);
        Ok(())
    }

    // TODO Move to instructions module
    fn write_entry_point(
        &mut self,
        entry_point: &crate::EntryPoint,
        info: &FunctionInfo,
        ir_module: &crate::Module,
        debug_info: &Option<DebugInfoInner>,
    ) -> Result<Instruction, Error> {
        let mut interface_ids = Vec::new();
        let function_id = self.write_function(
            &entry_point.function,
            info,
            ir_module,
            Some(FunctionInterface {
                varying_ids: &mut interface_ids,
                stage: entry_point.stage,
            }),
            debug_info,
        )?;

        let exec_model = match entry_point.stage {
            crate::ShaderStage::Vertex => spirv::ExecutionModel::Vertex,
            crate::ShaderStage::Fragment => {
                self.write_execution_mode(function_id, spirv::ExecutionMode::OriginUpperLeft)?;
                if let Some(ref result) = entry_point.function.result {
                    if contains_builtin(
                        result.binding.as_ref(),
                        result.ty,
                        &ir_module.types,
                        crate::BuiltIn::FragDepth,
                    ) {
                        self.write_execution_mode(
                            function_id,
                            spirv::ExecutionMode::DepthReplacing,
                        )?;
                    }
                }
                spirv::ExecutionModel::Fragment
            }
            crate::ShaderStage::Compute => {
                let execution_mode = spirv::ExecutionMode::LocalSize;
                //self.check(execution_mode.required_capabilities())?;
                Instruction::execution_mode(
                    function_id,
                    execution_mode,
                    &entry_point.workgroup_size,
                )
                .to_words(&mut self.logical_layout.execution_modes);
                spirv::ExecutionModel::GLCompute
            }
        };
        //self.check(exec_model.required_capabilities())?;

        Ok(Instruction::entry_point(
            exec_model,
            function_id,
            &entry_point.name,
            interface_ids.as_slice(),
        ))
    }

    fn make_scalar(&mut self, id: Word, scalar: crate::Scalar) -> Instruction {
        use crate::ScalarKind as Sk;

        let bits = (scalar.width * BITS_PER_BYTE) as u32;
        match scalar.kind {
            Sk::Sint | Sk::Uint => {
                let signedness = if scalar.kind == Sk::Sint {
                    super::instructions::Signedness::Signed
                } else {
                    super::instructions::Signedness::Unsigned
                };
                let cap = match bits {
                    8 => Some(spirv::Capability::Int8),
                    16 => Some(spirv::Capability::Int16),
                    64 => Some(spirv::Capability::Int64),
                    _ => None,
                };
                if let Some(cap) = cap {
                    self.capabilities_used.insert(cap);
                }
                Instruction::type_int(id, bits, signedness)
            }
            Sk::Float => {
                if bits == 64 {
                    self.capabilities_used.insert(spirv::Capability::Float64);
                }
                Instruction::type_float(id, bits)
            }
            Sk::Bool => Instruction::type_bool(id),
            Sk::AbstractInt | Sk::AbstractFloat => {
                unreachable!("abstract types should never reach the backend");
            }
        }
    }

    fn request_type_capabilities(&mut self, inner: &crate::TypeInner) -> Result<(), Error> {
        match *inner {
            crate::TypeInner::Image {
                dim,
                arrayed,
                class,
            } => {
                let sampled = match class {
                    crate::ImageClass::Sampled { .. } => true,
                    crate::ImageClass::Depth { .. } => true,
                    crate::ImageClass::Storage { format, .. } => {
                        self.request_image_format_capabilities(format.into())?;
                        false
                    }
                };

                match dim {
                    crate::ImageDimension::D1 => {
                        if sampled {
                            self.require_any("sampled 1D images", &[spirv::Capability::Sampled1D])?;
                        } else {
                            self.require_any("1D storage images", &[spirv::Capability::Image1D])?;
                        }
                    }
                    crate::ImageDimension::Cube if arrayed => {
                        if sampled {
                            self.require_any(
                                "sampled cube array images",
                                &[spirv::Capability::SampledCubeArray],
                            )?;
                        } else {
                            self.require_any(
                                "cube array storage images",
                                &[spirv::Capability::ImageCubeArray],
                            )?;
                        }
                    }
                    _ => {}
                }
            }
            crate::TypeInner::AccelerationStructure => {
                self.require_any("Acceleration Structure", &[spirv::Capability::RayQueryKHR])?;
            }
            crate::TypeInner::RayQuery => {
                self.require_any("Ray Query", &[spirv::Capability::RayQueryKHR])?;
            }
            crate::TypeInner::Atomic(crate::Scalar { width: 8, kind: _ }) => {
                self.require_any("64 bit integer atomics", &[spirv::Capability::Int64Atomics])?;
            }
            crate::TypeInner::Atomic(crate::Scalar {
                width: 4,
                kind: crate::ScalarKind::Float,
            }) => {
                self.require_any(
                    "32 bit floating-point atomics",
                    &[spirv::Capability::AtomicFloat32AddEXT],
                )?;
                self.use_extension("SPV_EXT_shader_atomic_float_add");
            }
            _ => {}
        }
        Ok(())
    }

    fn write_numeric_type_declaration_local(&mut self, id: Word, numeric: NumericType) {
        let instruction =
            match numeric {
                NumericType::Scalar(scalar) => self.make_scalar(id, scalar),
                NumericType::Vector { size, scalar } => {
                    let scalar_id = self.get_type_id(LookupType::Local(LocalType::Numeric(
                        NumericType::Scalar(scalar),
                    )));
                    Instruction::type_vector(id, scalar_id, size)
                }
                NumericType::Matrix {
                    columns,
                    rows,
                    scalar,
                } => {
                    let column_id = self.get_type_id(LookupType::Local(LocalType::Numeric(
                        NumericType::Vector { size: rows, scalar },
                    )));
                    Instruction::type_matrix(id, column_id, columns)
                }
            };

        instruction.to_words(&mut self.logical_layout.declarations);
    }

    fn write_type_declaration_local(&mut self, id: Word, local_ty: LocalType) {
        let instruction = match local_ty {
            LocalType::Numeric(numeric) => {
                self.write_numeric_type_declaration_local(id, numeric);
                return;
            }
            LocalType::LocalPointer { base, class } => {
                let base_id = self.get_type_id(LookupType::Local(LocalType::Numeric(base)));
                Instruction::type_pointer(id, class, base_id)
            }
            LocalType::Pointer { base, class } => {
                let type_id = self.get_type_id(LookupType::Handle(base));
                Instruction::type_pointer(id, class, type_id)
            }
            LocalType::Image(image) => {
                let local_type = LocalType::Numeric(NumericType::Scalar(image.sampled_type));
                let type_id = self.get_type_id(LookupType::Local(local_type));
                Instruction::type_image(id, type_id, image.dim, image.flags, image.image_format)
            }
            LocalType::Sampler => Instruction::type_sampler(id),
            LocalType::SampledImage { image_type_id } => {
                Instruction::type_sampled_image(id, image_type_id)
            }
            LocalType::BindingArray { base, size } => {
                let inner_ty = self.get_type_id(LookupType::Handle(base));
                let scalar_id = self.get_constant_scalar(crate::Literal::U32(size));
                Instruction::type_array(id, inner_ty, scalar_id)
            }
            LocalType::PointerToBindingArray { base, size, space } => {
                let inner_ty =
                    self.get_type_id(LookupType::Local(LocalType::BindingArray { base, size }));
                let class = map_storage_class(space);
                Instruction::type_pointer(id, class, inner_ty)
            }
            LocalType::AccelerationStructure => Instruction::type_acceleration_structure(id),
            LocalType::RayQuery => Instruction::type_ray_query(id),
        };

        instruction.to_words(&mut self.logical_layout.declarations);
    }

    fn write_type_declaration_arena(
        &mut self,
        arena: &UniqueArena<crate::Type>,
        handle: Handle<crate::Type>,
    ) -> Result<Word, Error> {
        let ty = &arena[handle];
        // If it's a type that needs SPIR-V capabilities, request them now.
        // This needs to happen regardless of the LocalType lookup succeeding,
        // because some types which map to the same LocalType have different
        // capability requirements. See https://github.com/gfx-rs/wgpu/issues/5569
        self.request_type_capabilities(&ty.inner)?;
        let id = if let Some(local) = LocalType::from_inner(&ty.inner) {
            // This type can be represented as a `LocalType`, so check if we've
            // already written an instruction for it. If not, do so now, with
            // `write_type_declaration_local`.
            match self.lookup_type.entry(LookupType::Local(local)) {
                // We already have an id for this `LocalType`.
                Entry::Occupied(e) => *e.get(),

                // It's a type we haven't seen before.
                Entry::Vacant(e) => {
                    let id = self.id_gen.next();
                    e.insert(id);

                    self.write_type_declaration_local(id, local);

                    id
                }
            }
        } else {
            use spirv::Decoration;

            let id = self.id_gen.next();
            let instruction = match ty.inner {
                crate::TypeInner::Array { base, size, stride } => {
                    self.decorate(id, Decoration::ArrayStride, &[stride]);

                    let type_id = self.get_type_id(LookupType::Handle(base));
                    match size {
                        crate::ArraySize::Constant(length) => {
                            let length_id = self.get_index_constant(length.get());
                            Instruction::type_array(id, type_id, length_id)
                        }
                        crate::ArraySize::Pending(_) => unreachable!(),
                        crate::ArraySize::Dynamic => Instruction::type_runtime_array(id, type_id),
                    }
                }
                crate::TypeInner::BindingArray { base, size } => {
                    let type_id = self.get_type_id(LookupType::Handle(base));
                    match size {
                        crate::ArraySize::Constant(length) => {
                            let length_id = self.get_index_constant(length.get());
                            Instruction::type_array(id, type_id, length_id)
                        }
                        crate::ArraySize::Pending(_) => unreachable!(),
                        crate::ArraySize::Dynamic => Instruction::type_runtime_array(id, type_id),
                    }
                }
                crate::TypeInner::Struct {
                    ref members,
                    span: _,
                } => {
                    let mut has_runtime_array = false;
                    let mut member_ids = Vec::with_capacity(members.len());
                    for (index, member) in members.iter().enumerate() {
                        let member_ty = &arena[member.ty];
                        match member_ty.inner {
                            crate::TypeInner::Array {
                                base: _,
                                size: crate::ArraySize::Dynamic,
                                stride: _,
                            } => {
                                has_runtime_array = true;
                            }
                            _ => (),
                        }
                        self.decorate_struct_member(id, index, member, arena)?;
                        let member_id = self.get_type_id(LookupType::Handle(member.ty));
                        member_ids.push(member_id);
                    }
                    if has_runtime_array {
                        self.decorate(id, Decoration::Block, &[]);
                    }
                    Instruction::type_struct(id, member_ids.as_slice())
                }

                // These all have TypeLocal representations, so they should have been
                // handled by `write_type_declaration_local` above.
                crate::TypeInner::Scalar(_)
                | crate::TypeInner::Atomic(_)
                | crate::TypeInner::Vector { .. }
                | crate::TypeInner::Matrix { .. }
                | crate::TypeInner::Pointer { .. }
                | crate::TypeInner::ValuePointer { .. }
                | crate::TypeInner::Image { .. }
                | crate::TypeInner::Sampler { .. }
                | crate::TypeInner::AccelerationStructure
                | crate::TypeInner::RayQuery => unreachable!(),
            };

            instruction.to_words(&mut self.logical_layout.declarations);
            id
        };

        // Add this handle as a new alias for that type.
        self.lookup_type.insert(LookupType::Handle(handle), id);

        if self.flags.contains(WriterFlags::DEBUG) {
            if let Some(ref name) = ty.name {
                self.debugs.push(Instruction::name(id, name));
            }
        }

        Ok(id)
    }

    fn request_image_format_capabilities(
        &mut self,
        format: spirv::ImageFormat,
    ) -> Result<(), Error> {
        use spirv::ImageFormat as If;
        match format {
            If::Rg32f
            | If::Rg16f
            | If::R11fG11fB10f
            | If::R16f
            | If::Rgba16
            | If::Rgb10A2
            | If::Rg16
            | If::Rg8
            | If::R16
            | If::R8
            | If::Rgba16Snorm
            | If::Rg16Snorm
            | If::Rg8Snorm
            | If::R16Snorm
            | If::R8Snorm
            | If::Rg32i
            | If::Rg16i
            | If::Rg8i
            | If::R16i
            | If::R8i
            | If::Rgb10a2ui
            | If::Rg32ui
            | If::Rg16ui
            | If::Rg8ui
            | If::R16ui
            | If::R8ui => self.require_any(
                "storage image format",
                &[spirv::Capability::StorageImageExtendedFormats],
            ),
            If::R64ui | If::R64i => self.require_any(
                "64-bit integer storage image format",
                &[spirv::Capability::Int64ImageEXT],
            ),
            If::Unknown
            | If::Rgba32f
            | If::Rgba16f
            | If::R32f
            | If::Rgba8
            | If::Rgba8Snorm
            | If::Rgba32i
            | If::Rgba16i
            | If::Rgba8i
            | If::R32i
            | If::Rgba32ui
            | If::Rgba16ui
            | If::Rgba8ui
            | If::R32ui => Ok(()),
        }
    }

    pub(super) fn get_index_constant(&mut self, index: Word) -> Word {
        self.get_constant_scalar(crate::Literal::U32(index))
    }

    pub(super) fn get_constant_scalar_with(
        &mut self,
        value: u8,
        scalar: crate::Scalar,
    ) -> Result<Word, Error> {
        Ok(
            self.get_constant_scalar(crate::Literal::new(value, scalar).ok_or(
                Error::Validation("Unexpected kind and/or width for Literal"),
            )?),
        )
    }

    pub(super) fn get_constant_scalar(&mut self, value: crate::Literal) -> Word {
        let scalar = CachedConstant::Literal(value.into());
        if let Some(&id) = self.cached_constants.get(&scalar) {
            return id;
        }
        let id = self.id_gen.next();
        self.write_constant_scalar(id, &value, None);
        self.cached_constants.insert(scalar, id);
        id
    }

    fn write_constant_scalar(
        &mut self,
        id: Word,
        value: &crate::Literal,
        debug_name: Option<&String>,
    ) {
        if self.flags.contains(WriterFlags::DEBUG) {
            if let Some(name) = debug_name {
                self.debugs.push(Instruction::name(id, name));
            }
        }
        let type_id = self.get_type_id(LookupType::Local(LocalType::Numeric(NumericType::Scalar(
            value.scalar(),
        ))));
        let instruction = match *value {
            crate::Literal::F64(value) => {
                let bits = value.to_bits();
                Instruction::constant_64bit(type_id, id, bits as u32, (bits >> 32) as u32)
            }
            crate::Literal::F32(value) => Instruction::constant_32bit(type_id, id, value.to_bits()),
            crate::Literal::U32(value) => Instruction::constant_32bit(type_id, id, value),
            crate::Literal::I32(value) => Instruction::constant_32bit(type_id, id, value as u32),
            crate::Literal::U64(value) => {
                Instruction::constant_64bit(type_id, id, value as u32, (value >> 32) as u32)
            }
            crate::Literal::I64(value) => {
                Instruction::constant_64bit(type_id, id, value as u32, (value >> 32) as u32)
            }
            crate::Literal::Bool(true) => Instruction::constant_true(type_id, id),
            crate::Literal::Bool(false) => Instruction::constant_false(type_id, id),
            crate::Literal::AbstractInt(_) | crate::Literal::AbstractFloat(_) => {
                unreachable!("Abstract types should not appear in IR presented to backends");
            }
        };

        instruction.to_words(&mut self.logical_layout.declarations);
    }

    pub(super) fn get_constant_composite(
        &mut self,
        ty: LookupType,
        constituent_ids: &[Word],
    ) -> Word {
        let composite = CachedConstant::Composite {
            ty,
            constituent_ids: constituent_ids.to_vec(),
        };
        if let Some(&id) = self.cached_constants.get(&composite) {
            return id;
        }
        let id = self.id_gen.next();
        self.write_constant_composite(id, ty, constituent_ids, None);
        self.cached_constants.insert(composite, id);
        id
    }

    fn write_constant_composite(
        &mut self,
        id: Word,
        ty: LookupType,
        constituent_ids: &[Word],
        debug_name: Option<&String>,
    ) {
        if self.flags.contains(WriterFlags::DEBUG) {
            if let Some(name) = debug_name {
                self.debugs.push(Instruction::name(id, name));
            }
        }
        let type_id = self.get_type_id(ty);
        Instruction::constant_composite(type_id, id, constituent_ids)
            .to_words(&mut self.logical_layout.declarations);
    }

    pub(super) fn get_constant_null(&mut self, type_id: Word) -> Word {
        let null = CachedConstant::ZeroValue(type_id);
        if let Some(&id) = self.cached_constants.get(&null) {
            return id;
        }
        let id = self.write_constant_null(type_id);
        self.cached_constants.insert(null, id);
        id
    }

    pub(super) fn write_constant_null(&mut self, type_id: Word) -> Word {
        let null_id = self.id_gen.next();
        Instruction::constant_null(type_id, null_id)
            .to_words(&mut self.logical_layout.declarations);
        null_id
    }

    fn write_constant_expr(
        &mut self,
        handle: Handle<crate::Expression>,
        ir_module: &crate::Module,
        mod_info: &ModuleInfo,
    ) -> Result<Word, Error> {
        let id = match ir_module.global_expressions[handle] {
            crate::Expression::Literal(literal) => self.get_constant_scalar(literal),
            crate::Expression::Constant(constant) => {
                let constant = &ir_module.constants[constant];
                self.constant_ids[constant.init]
            }
            crate::Expression::ZeroValue(ty) => {
                let type_id = self.get_type_id(LookupType::Handle(ty));
                self.get_constant_null(type_id)
            }
            crate::Expression::Compose { ty, ref components } => {
                let component_ids: Vec<_> = crate::proc::flatten_compose(
                    ty,
                    components,
                    &ir_module.global_expressions,
                    &ir_module.types,
                )
                .map(|component| self.constant_ids[component])
                .collect();
                self.get_constant_composite(LookupType::Handle(ty), component_ids.as_slice())
            }
            crate::Expression::Splat { size, value } => {
                let value_id = self.constant_ids[value];
                let component_ids = &[value_id; 4][..size as usize];

                let ty = self.get_expression_lookup_type(&mod_info[handle]);

                self.get_constant_composite(ty, component_ids)
            }
            _ => unreachable!(),
        };

        self.constant_ids[handle] = id;

        Ok(id)
    }

    pub(super) fn write_barrier(&mut self, flags: crate::Barrier, block: &mut Block) {
        let memory_scope = if flags.contains(crate::Barrier::STORAGE) {
            spirv::Scope::Device
        } else {
            spirv::Scope::Workgroup
        };
        let mut semantics = spirv::MemorySemantics::ACQUIRE_RELEASE;
        semantics.set(
            spirv::MemorySemantics::UNIFORM_MEMORY,
            flags.contains(crate::Barrier::STORAGE),
        );
        semantics.set(
            spirv::MemorySemantics::WORKGROUP_MEMORY,
            flags.contains(crate::Barrier::WORK_GROUP),
        );
        let exec_scope_id = if flags.contains(crate::Barrier::SUB_GROUP) {
            self.get_index_constant(spirv::Scope::Subgroup as u32)
        } else {
            self.get_index_constant(spirv::Scope::Workgroup as u32)
        };
        let mem_scope_id = self.get_index_constant(memory_scope as u32);
        let semantics_id = self.get_index_constant(semantics.bits());
        block.body.push(Instruction::control_barrier(
            exec_scope_id,
            mem_scope_id,
            semantics_id,
        ));
    }

    fn generate_workgroup_vars_init_block(
        &mut self,
        entry_id: Word,
        ir_module: &crate::Module,
        info: &FunctionInfo,
        local_invocation_id: Option<Word>,
        interface: &mut FunctionInterface,
        function: &mut Function,
    ) -> Option<Word> {
        let body = ir_module
            .global_variables
            .iter()
            .filter(|&(handle, var)| {
                !info[handle].is_empty() && var.space == crate::AddressSpace::WorkGroup
            })
            .map(|(handle, var)| {
                // It's safe to use `var_id` here, not `access_id`, because only
                // variables in the `Uniform` and `StorageBuffer` address spaces
                // get wrapped, and we're initializing `WorkGroup` variables.
                let var_id = self.global_variables[handle].var_id;
                let var_type_id = self.get_type_id(LookupType::Handle(var.ty));
                let init_word = self.get_constant_null(var_type_id);
                Instruction::store(var_id, init_word, None)
            })
            .collect::<Vec<_>>();

        if body.is_empty() {
            return None;
        }

        let uint3_type_id = self.get_uint3_type_id();

        let mut pre_if_block = Block::new(entry_id);

        let local_invocation_id = if let Some(local_invocation_id) = local_invocation_id {
            local_invocation_id
        } else {
            let varying_id = self.id_gen.next();
            let class = spirv::StorageClass::Input;
            let pointer_type_id = self.get_uint3_pointer_type_id(class);

            Instruction::variable(pointer_type_id, varying_id, class, None)
                .to_words(&mut self.logical_layout.declarations);

            self.decorate(
                varying_id,
                spirv::Decoration::BuiltIn,
                &[spirv::BuiltIn::LocalInvocationId as u32],
            );

            interface.varying_ids.push(varying_id);
            let id = self.id_gen.next();
            pre_if_block
                .body
                .push(Instruction::load(uint3_type_id, id, varying_id, None));

            id
        };

        let zero_id = self.get_constant_null(uint3_type_id);
        let bool3_type_id = self.get_bool3_type_id();

        let eq_id = self.id_gen.next();
        pre_if_block.body.push(Instruction::binary(
            spirv::Op::IEqual,
            bool3_type_id,
            eq_id,
            local_invocation_id,
            zero_id,
        ));

        let condition_id = self.id_gen.next();
        let bool_type_id = self.get_bool_type_id();
        pre_if_block.body.push(Instruction::relational(
            spirv::Op::All,
            bool_type_id,
            condition_id,
            eq_id,
        ));

        let merge_id = self.id_gen.next();
        pre_if_block.body.push(Instruction::selection_merge(
            merge_id,
            spirv::SelectionControl::NONE,
        ));

        let accept_id = self.id_gen.next();
        function.consume(
            pre_if_block,
            Instruction::branch_conditional(condition_id, accept_id, merge_id),
        );

        let accept_block = Block {
            label_id: accept_id,
            body,
        };
        function.consume(accept_block, Instruction::branch(merge_id));

        let mut post_if_block = Block::new(merge_id);

        self.write_barrier(crate::Barrier::WORK_GROUP, &mut post_if_block);

        let next_id = self.id_gen.next();
        function.consume(post_if_block, Instruction::branch(next_id));
        Some(next_id)
    }

    /// Generate an `OpVariable` for one value in an [`EntryPoint`]'s IO interface.
    ///
    /// The [`Binding`]s of the arguments and result of an [`EntryPoint`]'s
    /// [`Function`] describe a SPIR-V shader interface. In SPIR-V, the
    /// interface is represented by global variables in the `Input` and `Output`
    /// storage classes, with decorations indicating which builtin or location
    /// each variable corresponds to.
    ///
    /// This function emits a single global `OpVariable` for a single value from
    /// the interface, and adds appropriate decorations to indicate which
    /// builtin or location it represents, how it should be interpolated, and so
    /// on. The `class` argument gives the variable's SPIR-V storage class,
    /// which should be either [`Input`] or [`Output`].
    ///
    /// [`Binding`]: crate::Binding
    /// [`Function`]: crate::Function
    /// [`EntryPoint`]: crate::EntryPoint
    /// [`Input`]: spirv::StorageClass::Input
    /// [`Output`]: spirv::StorageClass::Output
    fn write_varying(
        &mut self,
        ir_module: &crate::Module,
        stage: crate::ShaderStage,
        class: spirv::StorageClass,
        debug_name: Option<&str>,
        ty: Handle<crate::Type>,
        binding: &crate::Binding,
    ) -> Result<Word, Error> {
        let id = self.id_gen.next();
        let pointer_type_id = self.get_pointer_id(ty, class);
        Instruction::variable(pointer_type_id, id, class, None)
            .to_words(&mut self.logical_layout.declarations);

        if self
            .flags
            .contains(WriterFlags::DEBUG | WriterFlags::LABEL_VARYINGS)
        {
            if let Some(name) = debug_name {
                self.debugs.push(Instruction::name(id, name));
            }
        }

        use spirv::{BuiltIn, Decoration};

        match *binding {
            crate::Binding::Location {
                location,
                interpolation,
                sampling,
                second_blend_source,
            } => {
                self.decorate(id, Decoration::Location, &[location]);

                let no_decorations =
                    // VUID-StandaloneSpirv-Flat-06202
                    // > The Flat, NoPerspective, Sample, and Centroid decorations
                    // > must not be used on variables with the Input storage class in a vertex shader
                    (class == spirv::StorageClass::Input && stage == crate::ShaderStage::Vertex) ||
                    // VUID-StandaloneSpirv-Flat-06201
                    // > The Flat, NoPerspective, Sample, and Centroid decorations
                    // > must not be used on variables with the Output storage class in a fragment shader
                    (class == spirv::StorageClass::Output && stage == crate::ShaderStage::Fragment);

                if !no_decorations {
                    match interpolation {
                        // Perspective-correct interpolation is the default in SPIR-V.
                        None | Some(crate::Interpolation::Perspective) => (),
                        Some(crate::Interpolation::Flat) => {
                            self.decorate(id, Decoration::Flat, &[]);
                        }
                        Some(crate::Interpolation::Linear) => {
                            self.decorate(id, Decoration::NoPerspective, &[]);
                        }
                    }
                    match sampling {
                        // Center sampling is the default in SPIR-V.
                        None
                        | Some(
                            crate::Sampling::Center
                            | crate::Sampling::First
                            | crate::Sampling::Either,
                        ) => (),
                        Some(crate::Sampling::Centroid) => {
                            self.decorate(id, Decoration::Centroid, &[]);
                        }
                        Some(crate::Sampling::Sample) => {
                            self.require_any(
                                "per-sample interpolation",
                                &[spirv::Capability::SampleRateShading],
                            )?;
                            self.decorate(id, Decoration::Sample, &[]);
                        }
                    }
                }
                if second_blend_source {
                    self.decorate(id, Decoration::Index, &[1]);
                }
            }
            crate::Binding::BuiltIn(built_in) => {
                use crate::BuiltIn as Bi;
                let built_in = match built_in {
                    Bi::Position { invariant } => {
                        if invariant {
                            self.decorate(id, Decoration::Invariant, &[]);
                        }

                        if class == spirv::StorageClass::Output {
                            BuiltIn::Position
                        } else {
                            BuiltIn::FragCoord
                        }
                    }
                    Bi::ViewIndex => {
                        self.require_any("`view_index` built-in", &[spirv::Capability::MultiView])?;
                        BuiltIn::ViewIndex
                    }
                    // vertex
                    Bi::BaseInstance => BuiltIn::BaseInstance,
                    Bi::BaseVertex => BuiltIn::BaseVertex,
                    Bi::ClipDistance => {
                        self.require_any(
                            "`clip_distance` built-in",
                            &[spirv::Capability::ClipDistance],
                        )?;
                        BuiltIn::ClipDistance
                    }
                    Bi::CullDistance => {
                        self.require_any(
                            "`cull_distance` built-in",
                            &[spirv::Capability::CullDistance],
                        )?;
                        BuiltIn::CullDistance
                    }
                    Bi::InstanceIndex => BuiltIn::InstanceIndex,
                    Bi::PointSize => BuiltIn::PointSize,
                    Bi::VertexIndex => BuiltIn::VertexIndex,
                    Bi::DrawID => BuiltIn::DrawIndex,
                    // fragment
                    Bi::FragDepth => BuiltIn::FragDepth,
                    Bi::PointCoord => BuiltIn::PointCoord,
                    Bi::FrontFacing => BuiltIn::FrontFacing,
                    Bi::PrimitiveIndex => {
                        self.require_any(
                            "`primitive_index` built-in",
                            &[spirv::Capability::Geometry],
                        )?;
                        BuiltIn::PrimitiveId
                    }
                    Bi::SampleIndex => {
                        self.require_any(
                            "`sample_index` built-in",
                            &[spirv::Capability::SampleRateShading],
                        )?;

                        BuiltIn::SampleId
                    }
                    Bi::SampleMask => BuiltIn::SampleMask,
                    // compute
                    Bi::GlobalInvocationId => BuiltIn::GlobalInvocationId,
                    Bi::LocalInvocationId => BuiltIn::LocalInvocationId,
                    Bi::LocalInvocationIndex => BuiltIn::LocalInvocationIndex,
                    Bi::WorkGroupId => BuiltIn::WorkgroupId,
                    Bi::WorkGroupSize => BuiltIn::WorkgroupSize,
                    Bi::NumWorkGroups => BuiltIn::NumWorkgroups,
                    // Subgroup
                    Bi::NumSubgroups => {
                        self.require_any(
                            "`num_subgroups` built-in",
                            &[spirv::Capability::GroupNonUniform],
                        )?;
                        BuiltIn::NumSubgroups
                    }
                    Bi::SubgroupId => {
                        self.require_any(
                            "`subgroup_id` built-in",
                            &[spirv::Capability::GroupNonUniform],
                        )?;
                        BuiltIn::SubgroupId
                    }
                    Bi::SubgroupSize => {
                        self.require_any(
                            "`subgroup_size` built-in",
                            &[
                                spirv::Capability::GroupNonUniform,
                                spirv::Capability::SubgroupBallotKHR,
                            ],
                        )?;
                        BuiltIn::SubgroupSize
                    }
                    Bi::SubgroupInvocationId => {
                        self.require_any(
                            "`subgroup_invocation_id` built-in",
                            &[
                                spirv::Capability::GroupNonUniform,
                                spirv::Capability::SubgroupBallotKHR,
                            ],
                        )?;
                        BuiltIn::SubgroupLocalInvocationId
                    }
                };

                self.decorate(id, Decoration::BuiltIn, &[built_in as u32]);

                use crate::ScalarKind as Sk;

                // Per the Vulkan spec, `VUID-StandaloneSpirv-Flat-04744`:
                //
                // > Any variable with integer or double-precision floating-
                // > point type and with Input storage class in a fragment
                // > shader, must be decorated Flat
--> --------------------

--> maximum size reached

--> --------------------