Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1315 insertions, 0 deletions

diff --git a/third_party/rust/cranelift-frontend/src/frontend.rs b/third_party/rust/cranelift-frontend/src/frontend.rs
new file mode 100644
index 0000000000..3b9263301a
--- /dev/null
+++ b/third_party/rust/cranelift-frontend/src/frontend.rs
@@ -0,0 +1,1315 @@
+//! A frontend for building Cranelift IR from other languages.
+use crate::ssa::{SSABuilder, SideEffects};
+use crate::variable::Variable;
+use cranelift_codegen::cursor::{Cursor, FuncCursor};
+use cranelift_codegen::entity::{EntitySet, SecondaryMap};
+use cranelift_codegen::ir;
+use cranelift_codegen::ir::function::DisplayFunction;
+use cranelift_codegen::ir::{
+    types, AbiParam, Block, DataFlowGraph, ExtFuncData, ExternalName, FuncRef, Function,
+    GlobalValue, GlobalValueData, Heap, HeapData, Inst, InstBuilder, InstBuilderBase,
+    InstructionData, JumpTable, JumpTableData, LibCall, MemFlags, SigRef, Signature, StackSlot,
+    StackSlotData, Type, Value, ValueLabel, ValueLabelAssignments, ValueLabelStart,
+};
+use cranelift_codegen::isa::{TargetFrontendConfig, TargetIsa};
+use cranelift_codegen::packed_option::PackedOption;
+
+/// Structure used for translating a series of functions into Cranelift IR.
+///
+/// In order to reduce memory reallocations when compiling multiple functions,
+/// `FunctionBuilderContext` holds various data structures which are cleared between
+/// functions, rather than dropped, preserving the underlying allocations.
+pub struct FunctionBuilderContext {
+    ssa: SSABuilder,
+    blocks: SecondaryMap<Block, BlockData>,
+    types: SecondaryMap<Variable, Type>,
+}
+
+/// Temporary object used to build a single Cranelift IR `Function`.
+pub struct FunctionBuilder<'a> {
+    /// The function currently being built.
+    /// This field is public so the function can be re-borrowed.
+    pub func: &'a mut Function,
+
+    /// Source location to assign to all new instructions.
+    srcloc: ir::SourceLoc,
+
+    func_ctx: &'a mut FunctionBuilderContext,
+    position: PackedOption<Block>,
+}
+
+#[derive(Clone, Default)]
+struct BlockData {
+    /// A Block is "pristine" iff no instructions have been added since the last
+    /// call to `switch_to_block()`.
+    pristine: bool,
+
+    /// A Block is "filled" iff a terminator instruction has been inserted since
+    /// the last call to `switch_to_block()`.
+    ///
+    /// A filled block cannot be pristine.
+    filled: bool,
+
+    /// Count of parameters not supplied implicitly by the SSABuilder.
+    user_param_count: usize,
+}
+
+impl FunctionBuilderContext {
+    /// Creates a FunctionBuilderContext structure. The structure is automatically cleared after
+    /// each [`FunctionBuilder`](struct.FunctionBuilder.html) completes translating a function.
+    pub fn new() -> Self {
+        Self {
+            ssa: SSABuilder::new(),
+            blocks: SecondaryMap::new(),
+            types: SecondaryMap::new(),
+        }
+    }
+
+    fn clear(&mut self) {
+        self.ssa.clear();
+        self.blocks.clear();
+        self.types.clear();
+    }
+
+    fn is_empty(&self) -> bool {
+        self.ssa.is_empty() && self.blocks.is_empty() && self.types.is_empty()
+    }
+}
+
+/// Implementation of the [`InstBuilder`](cranelift_codegen::ir::InstBuilder) that has
+/// one convenience method per Cranelift IR instruction.
+pub struct FuncInstBuilder<'short, 'long: 'short> {
+    builder: &'short mut FunctionBuilder<'long>,
+    block: Block,
+}
+
+impl<'short, 'long> FuncInstBuilder<'short, 'long> {
+    fn new(builder: &'short mut FunctionBuilder<'long>, block: Block) -> Self {
+        Self { builder, block }
+    }
+}
+
+impl<'short, 'long> InstBuilderBase<'short> for FuncInstBuilder<'short, 'long> {
+    fn data_flow_graph(&self) -> &DataFlowGraph {
+        &self.builder.func.dfg
+    }
+
+    fn data_flow_graph_mut(&mut self) -> &mut DataFlowGraph {
+        &mut self.builder.func.dfg
+    }
+
+    // This implementation is richer than `InsertBuilder` because we use the data of the
+    // instruction being inserted to add related info to the DFG and the SSA building system,
+    // and perform debug sanity checks.
+    fn build(self, data: InstructionData, ctrl_typevar: Type) -> (Inst, &'short mut DataFlowGraph) {
+        // We only insert the Block in the layout when an instruction is added to it
+        self.builder.ensure_inserted_block();
+
+        let inst = self.builder.func.dfg.make_inst(data.clone());
+        self.builder.func.dfg.make_inst_results(inst, ctrl_typevar);
+        self.builder.func.layout.append_inst(inst, self.block);
+        if !self.builder.srcloc.is_default() {
+            self.builder.func.srclocs[inst] = self.builder.srcloc;
+        }
+
+        if data.opcode().is_branch() {
+            match data.branch_destination() {
+                Some(dest_block) => {
+                    // If the user has supplied jump arguments we must adapt the arguments of
+                    // the destination block
+                    self.builder.declare_successor(dest_block, inst);
+                }
+                None => {
+                    // branch_destination() doesn't detect jump_tables
+                    // If jump table we declare all entries successor
+                    if let InstructionData::BranchTable {
+                        table, destination, ..
+                    } = data
+                    {
+                        // Unlike all other jumps/branches, jump tables are
+                        // capable of having the same successor appear
+                        // multiple times, so we must deduplicate.
+                        let mut unique = EntitySet::<Block>::new();
+                        for dest_block in self
+                            .builder
+                            .func
+                            .jump_tables
+                            .get(table)
+                            .expect("you are referencing an undeclared jump table")
+                            .iter()
+                            .filter(|&dest_block| unique.insert(*dest_block))
+                        {
+                            // Call `declare_block_predecessor` instead of `declare_successor` for
+                            // avoiding the borrow checker.
+                            self.builder.func_ctx.ssa.declare_block_predecessor(
+                                *dest_block,
+                                self.builder.position.unwrap(),
+                                inst,
+                            );
+                        }
+                        self.builder.declare_successor(destination, inst);
+                    }
+                }
+            }
+        }
+
+        if data.opcode().is_terminator() {
+            self.builder.fill_current_block()
+        }
+        (inst, &mut self.builder.func.dfg)
+    }
+}
+
+/// This module allows you to create a function in Cranelift IR in a straightforward way, hiding
+/// all the complexity of its internal representation.
+///
+/// The module is parametrized by one type which is the representation of variables in your
+/// origin language. It offers a way to conveniently append instruction to your program flow.
+/// You are responsible to split your instruction flow into extended blocks (declared with
+/// `create_block`) whose properties are:
+///
+/// - branch and jump instructions can only point at the top of extended blocks;
+/// - the last instruction of each block is a terminator instruction which has no natural successor,
+///   and those instructions can only appear at the end of extended blocks.
+///
+/// The parameters of Cranelift IR instructions are Cranelift IR values, which can only be created
+/// as results of other Cranelift IR instructions. To be able to create variables redefined multiple
+/// times in your program, use the `def_var` and `use_var` command, that will maintain the
+/// correspondence between your variables and Cranelift IR SSA values.
+///
+/// The first block for which you call `switch_to_block` will be assumed to be the beginning of
+/// the function.
+///
+/// At creation, a `FunctionBuilder` instance borrows an already allocated `Function` which it
+/// modifies with the information stored in the mutable borrowed
+/// [`FunctionBuilderContext`](struct.FunctionBuilderContext.html). The function passed in
+/// argument should be newly created with
+/// [`Function::with_name_signature()`](Function::with_name_signature), whereas the
+/// `FunctionBuilderContext` can be kept as is between two function translations.
+///
+/// # Errors
+///
+/// The functions below will panic in debug mode whenever you try to modify the Cranelift IR
+/// function in a way that violate the coherence of the code. For instance: switching to a new
+/// `Block` when you haven't filled the current one with a terminator instruction, inserting a
+/// return instruction with arguments that don't match the function's signature.
+impl<'a> FunctionBuilder<'a> {
+    /// Creates a new FunctionBuilder structure that will operate on a `Function` using a
+    /// `FunctionBuilderContext`.
+    pub fn new(func: &'a mut Function, func_ctx: &'a mut FunctionBuilderContext) -> Self {
+        debug_assert!(func_ctx.is_empty());
+        Self {
+            func,
+            srcloc: Default::default(),
+            func_ctx,
+            position: Default::default(),
+        }
+    }
+
+    /// Get the block that this builder is currently at.
+    pub fn current_block(&self) -> Option<Block> {
+        self.position.expand()
+    }
+
+    /// Set the source location that should be assigned to all new instructions.
+    pub fn set_srcloc(&mut self, srcloc: ir::SourceLoc) {
+        self.srcloc = srcloc;
+    }
+
+    /// Creates a new `Block` and returns its reference.
+    pub fn create_block(&mut self) -> Block {
+        let block = self.func.dfg.make_block();
+        self.func_ctx.ssa.declare_block(block);
+        self.func_ctx.blocks[block] = BlockData {
+            filled: false,
+            pristine: true,
+            user_param_count: 0,
+        };
+        block
+    }
+
+    /// Insert `block` in the layout *after* the existing block `after`.
+    pub fn insert_block_after(&mut self, block: Block, after: Block) {
+        self.func.layout.insert_block_after(block, after);
+    }
+
+    /// After the call to this function, new instructions will be inserted into the designated
+    /// block, in the order they are declared. You must declare the types of the Block arguments
+    /// you will use here.
+    ///
+    /// When inserting the terminator instruction (which doesn't have a fallthrough to its immediate
+    /// successor), the block will be declared filled and it will not be possible to append
+    /// instructions to it.
+    pub fn switch_to_block(&mut self, block: Block) {
+        // First we check that the previous block has been filled.
+        debug_assert!(
+            self.position.is_none()
+                || self.is_unreachable()
+                || self.is_pristine()
+                || self.is_filled(),
+            "you have to fill your block before switching"
+        );
+        // We cannot switch to a filled block
+        debug_assert!(
+            !self.func_ctx.blocks[block].filled,
+            "you cannot switch to a block which is already filled"
+        );
+
+        // Then we change the cursor position.
+        self.position = PackedOption::from(block);
+    }
+
+    /// Declares that all the predecessors of this block are known.
+    ///
+    /// Function to call with `block` as soon as the last branch instruction to `block` has been
+    /// created. Forgetting to call this method on every block will cause inconsistencies in the
+    /// produced functions.
+    pub fn seal_block(&mut self, block: Block) {
+        let side_effects = self.func_ctx.ssa.seal_block(block, self.func);
+        self.handle_ssa_side_effects(side_effects);
+    }
+
+    /// Effectively calls seal_block on all unsealed blocks in the function.
+    ///
+    /// It's more efficient to seal `Block`s as soon as possible, during
+    /// translation, but for frontends where this is impractical to do, this
+    /// function can be used at the end of translating all blocks to ensure
+    /// that everything is sealed.
+    pub fn seal_all_blocks(&mut self) {
+        let side_effects = self.func_ctx.ssa.seal_all_blocks(self.func);
+        self.handle_ssa_side_effects(side_effects);
+    }
+
+    /// In order to use a variable in a `use_var`, you need to declare its type with this method.
+    pub fn declare_var(&mut self, var: Variable, ty: Type) {
+        debug_assert_eq!(
+            self.func_ctx.types[var],
+            types::INVALID,
+            "variable {:?} is declared twice",
+            var
+        );
+        self.func_ctx.types[var] = ty;
+    }
+
+    /// Returns the Cranelift IR value corresponding to the utilization at the current program
+    /// position of a previously defined user variable.
+    pub fn use_var(&mut self, var: Variable) -> Value {
+        let (val, side_effects) = {
+            let ty = *self.func_ctx.types.get(var).unwrap_or_else(|| {
+                panic!(
+                    "variable {:?} is used but its type has not been declared",
+                    var
+                )
+            });
+            debug_assert_ne!(
+                ty,
+                types::INVALID,
+                "variable {:?} is used but its type has not been declared",
+                var
+            );
+            self.func_ctx
+                .ssa
+                .use_var(self.func, var, ty, self.position.unwrap())
+        };
+        self.handle_ssa_side_effects(side_effects);
+        val
+    }
+
+    /// Register a new definition of a user variable. The type of the value must be
+    /// the same as the type registered for the variable.
+    pub fn def_var(&mut self, var: Variable, val: Value) {
+        debug_assert_eq!(
+            *self.func_ctx.types.get(var).unwrap_or_else(|| panic!(
+                "variable {:?} is used but its type has not been declared",
+                var
+            )),
+            self.func.dfg.value_type(val),
+            "declared type of variable {:?} doesn't match type of value {}",
+            var,
+            val
+        );
+
+        self.func_ctx.ssa.def_var(var, val, self.position.unwrap());
+    }
+
+    /// Set label for Value
+    ///
+    /// This will not do anything unless `func.dfg.collect_debug_info` is called first.
+    pub fn set_val_label(&mut self, val: Value, label: ValueLabel) {
+        if let Some(values_labels) = self.func.dfg.values_labels.as_mut() {
+            use crate::hash_map::Entry;
+
+            let start = ValueLabelStart {
+                from: self.srcloc,
+                label,
+            };
+
+            match values_labels.entry(val) {
+                Entry::Occupied(mut e) => match e.get_mut() {
+                    ValueLabelAssignments::Starts(starts) => starts.push(start),
+                    _ => panic!("Unexpected ValueLabelAssignments at this stage"),
+                },
+                Entry::Vacant(e) => {
+                    e.insert(ValueLabelAssignments::Starts(vec![start]));
+                }
+            }
+        }
+    }
+
+    /// Creates a jump table in the function, to be used by `br_table` instructions.
+    pub fn create_jump_table(&mut self, data: JumpTableData) -> JumpTable {
+        self.func.create_jump_table(data)
+    }
+
+    /// Creates a stack slot in the function, to be used by `stack_load`, `stack_store` and
+    /// `stack_addr` instructions.
+    pub fn create_stack_slot(&mut self, data: StackSlotData) -> StackSlot {
+        self.func.create_stack_slot(data)
+    }
+
+    /// Adds a signature which can later be used to declare an external function import.
+    pub fn import_signature(&mut self, signature: Signature) -> SigRef {
+        self.func.import_signature(signature)
+    }
+
+    /// Declare an external function import.
+    pub fn import_function(&mut self, data: ExtFuncData) -> FuncRef {
+        self.func.import_function(data)
+    }
+
+    /// Declares a global value accessible to the function.
+    pub fn create_global_value(&mut self, data: GlobalValueData) -> GlobalValue {
+        self.func.create_global_value(data)
+    }
+
+    /// Declares a heap accessible to the function.
+    pub fn create_heap(&mut self, data: HeapData) -> Heap {
+        self.func.create_heap(data)
+    }
+
+    /// Returns an object with the [`InstBuilder`](cranelift_codegen::ir::InstBuilder)
+    /// trait that allows to conveniently append an instruction to the current `Block` being built.
+    pub fn ins<'short>(&'short mut self) -> FuncInstBuilder<'short, 'a> {
+        let block = self
+            .position
+            .expect("Please call switch_to_block before inserting instructions");
+        FuncInstBuilder::new(self, block)
+    }
+
+    /// Make sure that the current block is inserted in the layout.
+    pub fn ensure_inserted_block(&mut self) {
+        let block = self.position.unwrap();
+        if self.func_ctx.blocks[block].pristine {
+            if !self.func.layout.is_block_inserted(block) {
+                self.func.layout.append_block(block);
+            }
+            self.func_ctx.blocks[block].pristine = false;
+        } else {
+            debug_assert!(
+                !self.func_ctx.blocks[block].filled,
+                "you cannot add an instruction to a block already filled"
+            );
+        }
+    }
+
+    /// Returns a `FuncCursor` pointed at the current position ready for inserting instructions.
+    ///
+    /// This can be used to insert SSA code that doesn't need to access locals and that doesn't
+    /// need to know about `FunctionBuilder` at all.
+    pub fn cursor(&mut self) -> FuncCursor {
+        self.ensure_inserted_block();
+        FuncCursor::new(self.func)
+            .with_srcloc(self.srcloc)
+            .at_bottom(self.position.unwrap())
+    }
+
+    /// Append parameters to the given `Block` corresponding to the function
+    /// parameters. This can be used to set up the block parameters for the
+    /// entry block.
+    pub fn append_block_params_for_function_params(&mut self, block: Block) {
+        debug_assert!(
+            !self.func_ctx.ssa.has_any_predecessors(block),
+            "block parameters for function parameters should only be added to the entry block"
+        );
+
+        // These parameters count as "user" parameters here because they aren't
+        // inserted by the SSABuilder.
+        let user_param_count = &mut self.func_ctx.blocks[block].user_param_count;
+        for argtyp in &self.func.signature.params {
+            *user_param_count += 1;
+            self.func.dfg.append_block_param(block, argtyp.value_type);
+        }
+    }
+
+    /// Append parameters to the given `Block` corresponding to the function
+    /// return values. This can be used to set up the block parameters for a
+    /// function exit block.
+    pub fn append_block_params_for_function_returns(&mut self, block: Block) {
+        // These parameters count as "user" parameters here because they aren't
+        // inserted by the SSABuilder.
+        let user_param_count = &mut self.func_ctx.blocks[block].user_param_count;
+        for argtyp in &self.func.signature.returns {
+            *user_param_count += 1;
+            self.func.dfg.append_block_param(block, argtyp.value_type);
+        }
+    }
+
+    /// Declare that translation of the current function is complete. This
+    /// resets the state of the `FunctionBuilder` in preparation to be used
+    /// for another function.
+    pub fn finalize(&mut self) {
+        // Check that all the `Block`s are filled and sealed.
+        debug_assert!(
+            self.func_ctx.blocks.iter().all(
+                |(block, block_data)| block_data.pristine || self.func_ctx.ssa.is_sealed(block)
+            ),
+            "all blocks should be sealed before dropping a FunctionBuilder"
+        );
+        debug_assert!(
+            self.func_ctx
+                .blocks
+                .values()
+                .all(|block_data| block_data.pristine || block_data.filled),
+            "all blocks should be filled before dropping a FunctionBuilder"
+        );
+
+        // In debug mode, check that all blocks are valid basic blocks.
+        #[cfg(debug_assertions)]
+        {
+            // Iterate manually to provide more helpful error messages.
+            for block in self.func_ctx.blocks.keys() {
+                if let Err((inst, _msg)) = self.func.is_block_basic(block) {
+                    let inst_str = self.func.dfg.display_inst(inst, None);
+                    panic!("{} failed basic block invariants on {}", block, inst_str);
+                }
+            }
+        }
+
+        // Clear the state (but preserve the allocated buffers) in preparation
+        // for translation another function.
+        self.func_ctx.clear();
+
+        // Reset srcloc and position to initial states.
+        self.srcloc = Default::default();
+        self.position = Default::default();
+    }
+}
+
+/// All the functions documented in the previous block are write-only and help you build a valid
+/// Cranelift IR functions via multiple debug asserts. However, you might need to improve the
+/// performance of your translation perform more complex transformations to your Cranelift IR
+/// function. The functions below help you inspect the function you're creating and modify it
+/// in ways that can be unsafe if used incorrectly.
+impl<'a> FunctionBuilder<'a> {
+    /// Retrieves all the parameters for a `Block` currently inferred from the jump instructions
+    /// inserted that target it and the SSA construction.
+    pub fn block_params(&self, block: Block) -> &[Value] {
+        self.func.dfg.block_params(block)
+    }
+
+    /// Retrieves the signature with reference `sigref` previously added with `import_signature`.
+    pub fn signature(&self, sigref: SigRef) -> Option<&Signature> {
+        self.func.dfg.signatures.get(sigref)
+    }
+
+    /// Creates a parameter for a specific `Block` by appending it to the list of already existing
+    /// parameters.
+    ///
+    /// **Note:** this function has to be called at the creation of the `Block` before adding
+    /// instructions to it, otherwise this could interfere with SSA construction.
+    pub fn append_block_param(&mut self, block: Block, ty: Type) -> Value {
+        debug_assert!(
+            self.func_ctx.blocks[block].pristine,
+            "You can't add block parameters after adding any instruction"
+        );
+        debug_assert_eq!(
+            self.func_ctx.blocks[block].user_param_count,
+            self.func.dfg.num_block_params(block)
+        );
+        self.func_ctx.blocks[block].user_param_count += 1;
+        self.func.dfg.append_block_param(block, ty)
+    }
+
+    /// Returns the result values of an instruction.
+    pub fn inst_results(&self, inst: Inst) -> &[Value] {
+        self.func.dfg.inst_results(inst)
+    }
+
+    /// Changes the destination of a jump instruction after creation.
+    ///
+    /// **Note:** You are responsible for maintaining the coherence with the arguments of
+    /// other jump instructions.
+    pub fn change_jump_destination(&mut self, inst: Inst, new_dest: Block) {
+        let old_dest = self.func.dfg[inst]
+            .branch_destination_mut()
+            .expect("you want to change the jump destination of a non-jump instruction");
+        let pred = self.func_ctx.ssa.remove_block_predecessor(*old_dest, inst);
+        *old_dest = new_dest;
+        self.func_ctx
+            .ssa
+            .declare_block_predecessor(new_dest, pred, inst);
+    }
+
+    /// Returns `true` if and only if the current `Block` is sealed and has no predecessors declared.
+    ///
+    /// The entry block of a function is never unreachable.
+    pub fn is_unreachable(&self) -> bool {
+        let is_entry = match self.func.layout.entry_block() {
+            None => false,
+            Some(entry) => self.position.unwrap() == entry,
+        };
+        !is_entry
+            && self.func_ctx.ssa.is_sealed(self.position.unwrap())
+            && !self
+                .func_ctx
+                .ssa
+                .has_any_predecessors(self.position.unwrap())
+    }
+
+    /// Returns `true` if and only if no instructions have been added since the last call to
+    /// `switch_to_block`.
+    pub fn is_pristine(&self) -> bool {
+        self.func_ctx.blocks[self.position.unwrap()].pristine
+    }
+
+    /// Returns `true` if and only if a terminator instruction has been inserted since the
+    /// last call to `switch_to_block`.
+    pub fn is_filled(&self) -> bool {
+        self.func_ctx.blocks[self.position.unwrap()].filled
+    }
+
+    /// Returns a displayable object for the function as it is.
+    ///
+    /// Useful for debug purposes. Use it with `None` for standard printing.
+    // Clippy thinks the lifetime that follows is needless, but rustc needs it
+    #[cfg_attr(feature = "cargo-clippy", allow(clippy::needless_lifetimes))]
+    pub fn display<'b, I: Into<Option<&'b dyn TargetIsa>>>(&'b self, isa: I) -> DisplayFunction {
+        self.func.display(isa)
+    }
+}
+
+/// Helper functions
+impl<'a> FunctionBuilder<'a> {
+    /// Calls libc.memcpy
+    ///
+    /// Copies the `size` bytes from `src` to `dest`, assumes that `src + size`
+    /// won't overlap onto `dest`. If `dest` and `src` overlap, the behavior is
+    /// undefined. Applications in which `dest` and `src` might overlap should
+    /// use `call_memmove` instead.
+    pub fn call_memcpy(
+        &mut self,
+        config: TargetFrontendConfig,
+        dest: Value,
+        src: Value,
+        size: Value,
+    ) {
+        let pointer_type = config.pointer_type();
+        let signature = {
+            let mut s = Signature::new(config.default_call_conv);
+            s.params.push(AbiParam::new(pointer_type));
+            s.params.push(AbiParam::new(pointer_type));
+            s.params.push(AbiParam::new(pointer_type));
+            self.import_signature(s)
+        };
+
+        let libc_memcpy = self.import_function(ExtFuncData {
+            name: ExternalName::LibCall(LibCall::Memcpy),
+            signature,
+            colocated: false,
+        });
+
+        self.ins().call(libc_memcpy, &[dest, src, size]);
+    }
+
+    /// Optimised memcpy or memmove for small copies.
+    ///
+    /// # Codegen safety
+    ///
+    /// The following properties must hold to prevent UB:
+    ///
+    /// * `src_align` and `dest_align` are an upper-bound on the alignment of `src` respectively `dest`.
+    /// * If `non_overlapping` is true, then this must be correct.
+    pub fn emit_small_memory_copy(
+        &mut self,
+        config: TargetFrontendConfig,
+        dest: Value,
+        src: Value,
+        size: u64,
+        dest_align: u8,
+        src_align: u8,
+        non_overlapping: bool,
+    ) {
+        // Currently the result of guess work, not actual profiling.
+        const THRESHOLD: u64 = 4;
+
+        if size == 0 {
+            return;
+        }
+
+        let access_size = greatest_divisible_power_of_two(size);
+        assert!(
+            access_size.is_power_of_two(),
+            "`size` is not a power of two"
+        );
+        assert!(
+            access_size >= u64::from(::core::cmp::min(src_align, dest_align)),
+            "`size` is smaller than `dest` and `src`'s alignment value."
+        );
+
+        let (access_size, int_type) = if access_size <= 8 {
+            (access_size, Type::int((access_size * 8) as u16).unwrap())
+        } else {
+            (8, types::I64)
+        };
+
+        let load_and_store_amount = size / access_size;
+
+        if load_and_store_amount > THRESHOLD {
+            let size_value = self.ins().iconst(config.pointer_type(), size as i64);
+            if non_overlapping {
+                self.call_memcpy(config, dest, src, size_value);
+            } else {
+                self.call_memmove(config, dest, src, size_value);
+            }
+            return;
+        }
+
+        let mut flags = MemFlags::new();
+        flags.set_aligned();
+
+        // Load all of the memory first. This is necessary in case `dest` overlaps.
+        // It can also improve performance a bit.
+        let registers: smallvec::SmallVec<[_; THRESHOLD as usize]> = (0..load_and_store_amount)
+            .map(|i| {
+                let offset = (access_size * i) as i32;
+                (self.ins().load(int_type, flags, src, offset), offset)
+            })
+            .collect();
+
+        for (value, offset) in registers {
+            self.ins().store(flags, value, dest, offset);
+        }
+    }
+
+    /// Calls libc.memset
+    ///
+    /// Writes `size` bytes of i8 value `ch` to memory starting at `buffer`.
+    pub fn call_memset(
+        &mut self,
+        config: TargetFrontendConfig,
+        buffer: Value,
+        ch: Value,
+        size: Value,
+    ) {
+        let pointer_type = config.pointer_type();
+        let signature = {
+            let mut s = Signature::new(config.default_call_conv);
+            s.params.push(AbiParam::new(pointer_type));
+            s.params.push(AbiParam::new(types::I32));
+            s.params.push(AbiParam::new(pointer_type));
+            self.import_signature(s)
+        };
+
+        let libc_memset = self.import_function(ExtFuncData {
+            name: ExternalName::LibCall(LibCall::Memset),
+            signature,
+            colocated: false,
+        });
+
+        let ch = self.ins().uextend(types::I32, ch);
+        self.ins().call(libc_memset, &[buffer, ch, size]);
+    }
+
+    /// Calls libc.memset
+    ///
+    /// Writes `size` bytes of value `ch` to memory starting at `buffer`.
+    pub fn emit_small_memset(
+        &mut self,
+        config: TargetFrontendConfig,
+        buffer: Value,
+        ch: u8,
+        size: u64,
+        buffer_align: u8,
+    ) {
+        // Currently the result of guess work, not actual profiling.
+        const THRESHOLD: u64 = 4;
+
+        if size == 0 {
+            return;
+        }
+
+        let access_size = greatest_divisible_power_of_two(size);
+        assert!(
+            access_size.is_power_of_two(),
+            "`size` is not a power of two"
+        );
+        assert!(
+            access_size >= u64::from(buffer_align),
+            "`size` is smaller than `dest` and `src`'s alignment value."
+        );
+
+        let (access_size, int_type) = if access_size <= 8 {
+            (access_size, Type::int((access_size * 8) as u16).unwrap())
+        } else {
+            (8, types::I64)
+        };
+
+        let load_and_store_amount = size / access_size;
+
+        if load_and_store_amount > THRESHOLD {
+            let ch = self.ins().iconst(types::I8, i64::from(ch));
+            let size = self.ins().iconst(config.pointer_type(), size as i64);
+            self.call_memset(config, buffer, ch, size);
+        } else {
+            let mut flags = MemFlags::new();
+            flags.set_aligned();
+
+            let ch = u64::from(ch);
+            let raw_value = if int_type == types::I64 {
+                (ch << 32) | (ch << 16) | (ch << 8) | ch
+            } else if int_type == types::I32 {
+                (ch << 16) | (ch << 8) | ch
+            } else if int_type == types::I16 {
+                (ch << 8) | ch
+            } else {
+                assert_eq!(int_type, types::I8);
+                ch
+            };
+
+            let value = self.ins().iconst(int_type, raw_value as i64);
+            for i in 0..load_and_store_amount {
+                let offset = (access_size * i) as i32;
+                self.ins().store(flags, value, buffer, offset);
+            }
+        }
+    }
+
+    /// Calls libc.memmove
+    ///
+    /// Copies `size` bytes from memory starting at `source` to memory starting
+    /// at `dest`. `source` is always read before writing to `dest`.
+    pub fn call_memmove(
+        &mut self,
+        config: TargetFrontendConfig,
+        dest: Value,
+        source: Value,
+        size: Value,
+    ) {
+        let pointer_type = config.pointer_type();
+        let signature = {
+            let mut s = Signature::new(config.default_call_conv);
+            s.params.push(AbiParam::new(pointer_type));
+            s.params.push(AbiParam::new(pointer_type));
+            s.params.push(AbiParam::new(pointer_type));
+            self.import_signature(s)
+        };
+
+        let libc_memmove = self.import_function(ExtFuncData {
+            name: ExternalName::LibCall(LibCall::Memmove),
+            signature,
+            colocated: false,
+        });
+
+        self.ins().call(libc_memmove, &[dest, source, size]);
+    }
+}
+
+fn greatest_divisible_power_of_two(size: u64) -> u64 {
+    (size as i64 & -(size as i64)) as u64
+}
+
+// Helper functions
+impl<'a> FunctionBuilder<'a> {
+    /// A Block is 'filled' when a terminator instruction is present.
+    fn fill_current_block(&mut self) {
+        self.func_ctx.blocks[self.position.unwrap()].filled = true;
+    }
+
+    fn declare_successor(&mut self, dest_block: Block, jump_inst: Inst) {
+        self.func_ctx
+            .ssa
+            .declare_block_predecessor(dest_block, self.position.unwrap(), jump_inst);
+    }
+
+    fn handle_ssa_side_effects(&mut self, side_effects: SideEffects) {
+        for split_block in side_effects.split_blocks_created {
+            self.func_ctx.blocks[split_block].filled = true
+        }
+        for modified_block in side_effects.instructions_added_to_blocks {
+            self.func_ctx.blocks[modified_block].pristine = false
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::greatest_divisible_power_of_two;
+    use crate::frontend::{FunctionBuilder, FunctionBuilderContext};
+    use crate::Variable;
+    use alloc::string::ToString;
+    use cranelift_codegen::entity::EntityRef;
+    use cranelift_codegen::ir::types::*;
+    use cranelift_codegen::ir::{AbiParam, ExternalName, Function, InstBuilder, Signature};
+    use cranelift_codegen::isa::CallConv;
+    use cranelift_codegen::settings;
+    use cranelift_codegen::verifier::verify_function;
+
+    fn sample_function(lazy_seal: bool) {
+        let mut sig = Signature::new(CallConv::SystemV);
+        sig.returns.push(AbiParam::new(I32));
+        sig.params.push(AbiParam::new(I32));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let block1 = builder.create_block();
+            let block2 = builder.create_block();
+            let block3 = builder.create_block();
+            let x = Variable::new(0);
+            let y = Variable::new(1);
+            let z = Variable::new(2);
+            builder.declare_var(x, I32);
+            builder.declare_var(y, I32);
+            builder.declare_var(z, I32);
+            builder.append_block_params_for_function_params(block0);
+
+            builder.switch_to_block(block0);
+            if !lazy_seal {
+                builder.seal_block(block0);
+            }
+            {
+                let tmp = builder.block_params(block0)[0]; // the first function parameter
+                builder.def_var(x, tmp);
+            }
+            {
+                let tmp = builder.ins().iconst(I32, 2);
+                builder.def_var(y, tmp);
+            }
+            {
+                let arg1 = builder.use_var(x);
+                let arg2 = builder.use_var(y);
+                let tmp = builder.ins().iadd(arg1, arg2);
+                builder.def_var(z, tmp);
+            }
+            builder.ins().jump(block1, &[]);
+
+            builder.switch_to_block(block1);
+            {
+                let arg1 = builder.use_var(y);
+                let arg2 = builder.use_var(z);
+                let tmp = builder.ins().iadd(arg1, arg2);
+                builder.def_var(z, tmp);
+            }
+            {
+                let arg = builder.use_var(y);
+                builder.ins().brnz(arg, block3, &[]);
+            }
+            builder.ins().jump(block2, &[]);
+
+            builder.switch_to_block(block2);
+            if !lazy_seal {
+                builder.seal_block(block2);
+            }
+            {
+                let arg1 = builder.use_var(z);
+                let arg2 = builder.use_var(x);
+                let tmp = builder.ins().isub(arg1, arg2);
+                builder.def_var(z, tmp);
+            }
+            {
+                let arg = builder.use_var(y);
+                builder.ins().return_(&[arg]);
+            }
+
+            builder.switch_to_block(block3);
+            if !lazy_seal {
+                builder.seal_block(block3);
+            }
+
+            {
+                let arg1 = builder.use_var(y);
+                let arg2 = builder.use_var(x);
+                let tmp = builder.ins().isub(arg1, arg2);
+                builder.def_var(y, tmp);
+            }
+            builder.ins().jump(block1, &[]);
+            if !lazy_seal {
+                builder.seal_block(block1);
+            }
+
+            if lazy_seal {
+                builder.seal_all_blocks();
+            }
+
+            builder.finalize();
+        }
+
+        let flags = settings::Flags::new(settings::builder());
+        // println!("{}", func.display(None));
+        if let Err(errors) = verify_function(&func, &flags) {
+            panic!("{}\n{}", func.display(None), errors)
+        }
+    }
+
+    #[test]
+    fn sample() {
+        sample_function(false)
+    }
+
+    #[test]
+    fn sample_with_lazy_seal() {
+        sample_function(true)
+    }
+
+    #[test]
+    fn memcpy() {
+        use core::str::FromStr;
+        use cranelift_codegen::{isa, settings};
+
+        let shared_builder = settings::builder();
+        let shared_flags = settings::Flags::new(shared_builder);
+
+        let triple =
+            ::target_lexicon::Triple::from_str("riscv32").expect("Couldn't create riscv32 triple");
+
+        let target = isa::lookup(triple)
+            .ok()
+            .map(|b| b.finish(shared_flags))
+            .expect("This test requires riscv32 support.");
+
+        let mut sig = Signature::new(target.default_call_conv());
+        sig.returns.push(AbiParam::new(I32));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let x = Variable::new(0);
+            let y = Variable::new(1);
+            let z = Variable::new(2);
+            builder.declare_var(x, target.pointer_type());
+            builder.declare_var(y, target.pointer_type());
+            builder.declare_var(z, I32);
+            builder.append_block_params_for_function_params(block0);
+            builder.switch_to_block(block0);
+
+            let src = builder.use_var(x);
+            let dest = builder.use_var(y);
+            let size = builder.use_var(y);
+            builder.call_memcpy(target.frontend_config(), dest, src, size);
+            builder.ins().return_(&[size]);
+
+            builder.seal_all_blocks();
+            builder.finalize();
+        }
+
+        assert_eq!(
+            func.display(None).to_string(),
+            "function %sample() -> i32 system_v {
+    sig0 = (i32, i32, i32) system_v
+    fn0 = %Memcpy sig0
+
+block0:
+    v3 = iconst.i32 0
+    v1 -> v3
+    v2 = iconst.i32 0
+    v0 -> v2
+    call fn0(v1, v0, v1)
+    return v1
+}
+"
+        );
+    }
+
+    #[test]
+    fn small_memcpy() {
+        use core::str::FromStr;
+        use cranelift_codegen::{isa, settings};
+
+        let shared_builder = settings::builder();
+        let shared_flags = settings::Flags::new(shared_builder);
+
+        let triple =
+            ::target_lexicon::Triple::from_str("riscv32").expect("Couldn't create riscv32 triple");
+
+        let target = isa::lookup(triple)
+            .ok()
+            .map(|b| b.finish(shared_flags))
+            .expect("This test requires riscv32 support.");
+
+        let mut sig = Signature::new(target.default_call_conv());
+        sig.returns.push(AbiParam::new(I32));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let x = Variable::new(0);
+            let y = Variable::new(16);
+            builder.declare_var(x, target.pointer_type());
+            builder.declare_var(y, target.pointer_type());
+            builder.append_block_params_for_function_params(block0);
+            builder.switch_to_block(block0);
+
+            let src = builder.use_var(x);
+            let dest = builder.use_var(y);
+            let size = 8;
+            builder.emit_small_memory_copy(target.frontend_config(), dest, src, size, 8, 8, true);
+            builder.ins().return_(&[dest]);
+
+            builder.seal_all_blocks();
+            builder.finalize();
+        }
+
+        assert_eq!(
+            func.display(None).to_string(),
+            "function %sample() -> i32 system_v {
+block0:
+    v4 = iconst.i32 0
+    v1 -> v4
+    v3 = iconst.i32 0
+    v0 -> v3
+    v2 = load.i64 aligned v0
+    store aligned v2, v1
+    return v1
+}
+"
+        );
+    }
+
+    #[test]
+    fn not_so_small_memcpy() {
+        use core::str::FromStr;
+        use cranelift_codegen::{isa, settings};
+
+        let shared_builder = settings::builder();
+        let shared_flags = settings::Flags::new(shared_builder);
+
+        let triple =
+            ::target_lexicon::Triple::from_str("riscv32").expect("Couldn't create riscv32 triple");
+
+        let target = isa::lookup(triple)
+            .ok()
+            .map(|b| b.finish(shared_flags))
+            .expect("This test requires riscv32 support.");
+
+        let mut sig = Signature::new(target.default_call_conv());
+        sig.returns.push(AbiParam::new(I32));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let x = Variable::new(0);
+            let y = Variable::new(16);
+            builder.declare_var(x, target.pointer_type());
+            builder.declare_var(y, target.pointer_type());
+            builder.append_block_params_for_function_params(block0);
+            builder.switch_to_block(block0);
+
+            let src = builder.use_var(x);
+            let dest = builder.use_var(y);
+            let size = 8192;
+            builder.emit_small_memory_copy(target.frontend_config(), dest, src, size, 8, 8, true);
+            builder.ins().return_(&[dest]);
+
+            builder.seal_all_blocks();
+            builder.finalize();
+        }
+
+        assert_eq!(
+            func.display(None).to_string(),
+            "function %sample() -> i32 system_v {
+    sig0 = (i32, i32, i32) system_v
+    fn0 = %Memcpy sig0
+
+block0:
+    v4 = iconst.i32 0
+    v1 -> v4
+    v3 = iconst.i32 0
+    v0 -> v3
+    v2 = iconst.i32 8192
+    call fn0(v1, v0, v2)
+    return v1
+}
+"
+        );
+    }
+
+    #[test]
+    fn small_memset() {
+        use core::str::FromStr;
+        use cranelift_codegen::{isa, settings};
+
+        let shared_builder = settings::builder();
+        let shared_flags = settings::Flags::new(shared_builder);
+
+        let triple =
+            ::target_lexicon::Triple::from_str("riscv32").expect("Couldn't create riscv32 triple");
+
+        let target = isa::lookup(triple)
+            .ok()
+            .map(|b| b.finish(shared_flags))
+            .expect("This test requires riscv32 support.");
+
+        let mut sig = Signature::new(target.default_call_conv());
+        sig.returns.push(AbiParam::new(I32));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let y = Variable::new(16);
+            builder.declare_var(y, target.pointer_type());
+            builder.append_block_params_for_function_params(block0);
+            builder.switch_to_block(block0);
+
+            let dest = builder.use_var(y);
+            let size = 8;
+            builder.emit_small_memset(target.frontend_config(), dest, 1, size, 8);
+            builder.ins().return_(&[dest]);
+
+            builder.seal_all_blocks();
+            builder.finalize();
+        }
+
+        assert_eq!(
+            func.display(None).to_string(),
+            "function %sample() -> i32 system_v {
+block0:
+    v2 = iconst.i32 0
+    v0 -> v2
+    v1 = iconst.i64 0x0001_0001_0101
+    store aligned v1, v0
+    return v0
+}
+"
+        );
+    }
+
+    #[test]
+    fn not_so_small_memset() {
+        use core::str::FromStr;
+        use cranelift_codegen::{isa, settings};
+
+        let shared_builder = settings::builder();
+        let shared_flags = settings::Flags::new(shared_builder);
+
+        let triple =
+            ::target_lexicon::Triple::from_str("riscv32").expect("Couldn't create riscv32 triple");
+
+        let target = isa::lookup(triple)
+            .ok()
+            .map(|b| b.finish(shared_flags))
+            .expect("This test requires riscv32 support.");
+
+        let mut sig = Signature::new(target.default_call_conv());
+        sig.returns.push(AbiParam::new(I32));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let y = Variable::new(16);
+            builder.declare_var(y, target.pointer_type());
+            builder.append_block_params_for_function_params(block0);
+            builder.switch_to_block(block0);
+
+            let dest = builder.use_var(y);
+            let size = 8192;
+            builder.emit_small_memset(target.frontend_config(), dest, 1, size, 8);
+            builder.ins().return_(&[dest]);
+
+            builder.seal_all_blocks();
+            builder.finalize();
+        }
+
+        assert_eq!(
+            func.display(None).to_string(),
+            "function %sample() -> i32 system_v {
+    sig0 = (i32, i32, i32) system_v
+    fn0 = %Memset sig0
+
+block0:
+    v4 = iconst.i32 0
+    v0 -> v4
+    v1 = iconst.i8 1
+    v2 = iconst.i32 8192
+    v3 = uextend.i32 v1
+    call fn0(v0, v3, v2)
+    return v0
+}
+"
+        );
+    }
+
+    #[test]
+    fn undef_vector_vars() {
+        let mut sig = Signature::new(CallConv::SystemV);
+        sig.returns.push(AbiParam::new(I8X16));
+        sig.returns.push(AbiParam::new(B8X16));
+        sig.returns.push(AbiParam::new(F32X4));
+
+        let mut fn_ctx = FunctionBuilderContext::new();
+        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
+        {
+            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);
+
+            let block0 = builder.create_block();
+            let a = Variable::new(0);
+            let b = Variable::new(1);
+            let c = Variable::new(2);
+            builder.declare_var(a, I8X16);
+            builder.declare_var(b, B8X16);
+            builder.declare_var(c, F32X4);
+            builder.switch_to_block(block0);
+
+            let a = builder.use_var(a);
+            let b = builder.use_var(b);
+            let c = builder.use_var(c);
+            builder.ins().return_(&[a, b, c]);
+
+            builder.seal_all_blocks();
+            builder.finalize();
+        }
+
+        assert_eq!(
+            func.display(None).to_string(),
+            "function %sample() -> i8x16, b8x16, f32x4 system_v {
+    const0 = 0x00000000000000000000000000000000
+
+block0:
+    v5 = f32const 0.0
+    v6 = splat.f32x4 v5
+    v2 -> v6
+    v4 = vconst.b8x16 const0
+    v1 -> v4
+    v3 = vconst.i8x16 const0
+    v0 -> v3
+    return v0, v1, v2
+}
+"
+        );
+    }
+
+    #[test]
+    fn test_greatest_divisible_power_of_two() {
+        assert_eq!(64, greatest_divisible_power_of_two(64));
+        assert_eq!(16, greatest_divisible_power_of_two(48));
+        assert_eq!(8, greatest_divisible_power_of_two(24));
+        assert_eq!(1, greatest_divisible_power_of_two(25));
+    }
+}