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//! This module implements lowering (instruction selection) from Cranelift IR
//! to machine instructions with virtual registers. This is *almost* the final
//! machine code, except for register allocation.
use crate::entity::SecondaryMap;
use crate::fx::{FxHashMap, FxHashSet};
use crate::inst_predicates::{has_lowering_side_effect, is_constant_64bit};
use crate::ir::instructions::BranchInfo;
use crate::ir::types::I64;
use crate::ir::{
ArgumentPurpose, Block, Constant, ConstantData, ExternalName, Function, GlobalValueData,
Immediate, Inst, InstructionData, MemFlags, Opcode, Signature, SourceLoc, Type, Value,
use crate::machinst::{
ABICallee, BlockIndex, BlockLoweringOrder, LoweredBlock, MachLabel, VCode, VCodeBuilder,
use crate::CodegenResult;
use regalloc::{Reg, RegClass, StackmapRequestInfo, VirtualReg, Writable};
use alloc::boxed::Box;
use alloc::vec::Vec;
use log::debug;
use smallvec::SmallVec;
/// An "instruction color" partitions CLIF instructions by side-effecting ops.
/// All instructions with the same "color" are guaranteed not to be separated by
/// any side-effecting op (for this purpose, loads are also considered
/// side-effecting, to avoid subtle questions w.r.t. the memory model), and
/// furthermore, it is guaranteed that for any two instructions A and B such
/// that color(A) == color(B), either A dominates B and B postdominates A, or
/// vice-versa. (For now, in practice, only ops in the same basic block can ever
/// have the same color, trivially providing the second condition.) Intuitively,
/// this means that the ops of the same color must always execute "together", as
/// part of one atomic contiguous section of the dynamic execution trace, and
/// they can be freely permuted (modulo true dataflow dependencies) without
/// affecting program behavior.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct InstColor(u32);
impl InstColor {
fn new(n: u32) -> InstColor {
/// Get an arbitrary index representing this color. The index is unique
/// *within a single function compilation*, but indices may be reused across
/// functions.
pub fn get(self) -> u32 {
/// A context that machine-specific lowering code can use to emit lowered
/// instructions. This is the view of the machine-independent per-function
/// lowering context that is seen by the machine backend.
pub trait LowerCtx {
/// The instruction type for which this lowering framework is instantiated.
type I: VCodeInst;
// Function-level queries:
/// Get the `ABICallee`.
fn abi(&mut self) -> &dyn ABICallee<I = Self::I>;
/// Get the (virtual) register that receives the return value. A return
/// instruction should lower into a sequence that fills this register. (Why
/// not allow the backend to specify its own result register for the return?
/// Because there may be multiple return points.)
fn retval(&self, idx: usize) -> Writable<Reg>;
/// Returns the vreg containing the VmContext parameter, if there's one.
fn get_vm_context(&self) -> Option<Reg>;
// General instruction queries:
/// Get the instdata for a given IR instruction.
fn data(&self, ir_inst: Inst) -> &InstructionData;
/// Get the controlling type for a polymorphic IR instruction.
fn ty(&self, ir_inst: Inst) -> Type;
/// Get the target for a call instruction, as an `ExternalName`. Returns a tuple
/// providing this name and the "relocation distance", i.e., whether the backend
/// can assume the target will be "nearby" (within some small offset) or an
/// arbitrary address. (This comes from the `colocated` bit in the CLIF.)
fn call_target<'b>(&'b self, ir_inst: Inst) -> Option<(&'b ExternalName, RelocDistance)>;
/// Get the signature for a call or call-indirect instruction.
fn call_sig<'b>(&'b self, ir_inst: Inst) -> Option<&'b Signature>;
/// Get the symbol name, relocation distance estimate, and offset for a
/// symbol_value instruction.
fn symbol_value<'b>(&'b self, ir_inst: Inst) -> Option<(&'b ExternalName, RelocDistance, i64)>;
/// Returns the memory flags of a given memory access.
fn memflags(&self, ir_inst: Inst) -> Option<MemFlags>;
/// Get the source location for a given instruction.
fn srcloc(&self, ir_inst: Inst) -> SourceLoc;
/// Get the side-effect color of the given instruction (specifically, at the
/// program point just prior to the instruction). The "color" changes at
/// every side-effecting op; the backend should not try to merge across
/// side-effect colors unless the op being merged is known to be pure.
fn inst_color(&self, ir_inst: Inst) -> InstColor;
// Instruction input/output queries:
/// Get the number of inputs to the given IR instruction.
fn num_inputs(&self, ir_inst: Inst) -> usize;
/// Get the number of outputs to the given IR instruction.
fn num_outputs(&self, ir_inst: Inst) -> usize;
/// Get the type for an instruction's input.
fn input_ty(&self, ir_inst: Inst, idx: usize) -> Type;
/// Get the type for an instruction's output.
fn output_ty(&self, ir_inst: Inst, idx: usize) -> Type;
/// Get the value of a constant instruction (`iconst`, etc.) as a 64-bit
/// value, if possible.
fn get_constant(&self, ir_inst: Inst) -> Option<u64>;
/// Get the input in any combination of three forms:
/// - An instruction, if the same color as this instruction or if the
/// producing instruction has no side effects (thus in both cases
/// mergeable);
/// - A constant, if the value is a constant;
/// - A register.
/// The instruction input may be available in some or all of these
/// forms. More than one is possible: e.g., it may be produced by an
/// instruction in the same block, but may also have been forced into a
/// register already by an earlier op. It will *always* be available
/// in a register, at least.
/// If the backend uses the register, rather than one of the other
/// forms (constant or merging of the producing op), it must call
/// `use_input_reg()` to ensure the producing inst is actually lowered
/// as well. Failing to do so may result in the instruction that generates
/// this value never being generated, thus resulting in incorrect execution.
/// For correctness, backends should thus wrap `get_input()` and
/// `use_input_regs()` with helpers that return a register only after
/// ensuring it is marked as used.
fn get_input(&self, ir_inst: Inst, idx: usize) -> LowerInput;
/// Get the `idx`th output register of the given IR instruction. When
/// `backend.lower_inst_to_regs(ctx, inst)` is called, it is expected that
/// the backend will write results to these output register(s). This
/// register will always be "fresh"; it is guaranteed not to overlap with
/// any of the inputs, and can be freely used as a scratch register within
/// the lowered instruction sequence, as long as its final value is the
/// result of the computation.
fn get_output(&self, ir_inst: Inst, idx: usize) -> Writable<Reg>;
// Codegen primitives: allocate temps, emit instructions, set result registers,
// ask for an input to be gen'd into a register.
/// Get a new temp.
fn alloc_tmp(&mut self, rc: RegClass, ty: Type) -> Writable<Reg>;
/// Emit a machine instruction.
fn emit(&mut self, mach_inst: Self::I);
/// Emit a machine instruction that is a safepoint.
fn emit_safepoint(&mut self, mach_inst: Self::I);
/// Indicate that the given input uses the register returned by
/// `get_input()`. Codegen may not happen otherwise for the producing
/// instruction if it has no side effects and no uses.
fn use_input_reg(&mut self, input: LowerInput);
/// Is the given register output needed after the given instruction? Allows
/// instructions with multiple outputs to make fine-grained decisions on
/// which outputs to actually generate.
fn is_reg_needed(&self, ir_inst: Inst, reg: Reg) -> bool;
/// Retrieve constant data given a handle.
fn get_constant_data(&self, constant_handle: Constant) -> &ConstantData;
/// Retrieve an immediate given a reference.
fn get_immediate(&self, imm: Immediate) -> &ConstantData;
/// Cause the value in `reg` to be in a virtual reg, by copying it into a new virtual reg
/// if `reg` is a real reg. `ty` describes the type of the value in `reg`.
fn ensure_in_vreg(&mut self, reg: Reg, ty: Type) -> Reg;
/// A representation of all of the ways in which an instruction input is
/// available: as a producing instruction (in the same color-partition), as a
/// constant, and/or in an existing register. See [LowerCtx::get_input] for more
/// details.
#[derive(Clone, Copy, Debug)]
pub struct LowerInput {
/// The value is live in a register. This option is always available. Call
/// [LowerCtx::use_input_reg()] if the register is used.
pub reg: Reg,
/// An instruction produces this value; the instruction's result index that
/// produces this value is given.
pub inst: Option<(Inst, usize)>,
/// The value is a known constant.
pub constant: Option<u64>,
/// A machine backend.
pub trait LowerBackend {
/// The machine instruction type.
type MInst: VCodeInst;
/// Lower a single instruction.
/// For a branch, this function should not generate the actual branch
/// instruction. However, it must force any values it needs for the branch
/// edge (block-param actuals) into registers, because the actual branch
/// generation (`lower_branch_group()`) happens *after* any possible merged
/// out-edge.
fn lower<C: LowerCtx<I = Self::MInst>>(&self, ctx: &mut C, inst: Inst) -> CodegenResult<()>;
/// Lower a block-terminating group of branches (which together can be seen
/// as one N-way branch), given a vcode MachLabel for each target.
fn lower_branch_group<C: LowerCtx<I = Self::MInst>>(
ctx: &mut C,
insts: &[Inst],
targets: &[MachLabel],
fallthrough: Option<MachLabel>,
) -> CodegenResult<()>;
/// A bit of a hack: give a fixed register that always holds the result of a
/// `get_pinned_reg` instruction, if known. This allows elision of moves
/// into the associated vreg, instead using the real reg directly.
fn maybe_pinned_reg(&self) -> Option<Reg> {
/// A pending instruction to insert and auxiliary information about it: its source location and
/// whether it is a safepoint.
struct InstTuple<I: VCodeInst> {
loc: SourceLoc,
is_safepoint: bool,
inst: I,
/// Machine-independent lowering driver / machine-instruction container. Maintains a correspondence
/// from original Inst to MachInsts.
pub struct Lower<'func, I: VCodeInst> {
/// The function to lower.
f: &'func Function,
/// Lowered machine instructions.
vcode: VCodeBuilder<I>,
/// Mapping from `Value` (SSA value in IR) to virtual register.
value_regs: SecondaryMap<Value, Reg>,
/// Return-value vregs.
retval_regs: Vec<Reg>,
/// Instruction colors.
inst_colors: SecondaryMap<Inst, InstColor>,
/// Instruction constant values, if known.
inst_constants: FxHashMap<Inst, u64>,
/// Instruction has a side-effect and must be codegen'd.
inst_needed: SecondaryMap<Inst, bool>,
/// Value (vreg) is needed and producer must be codegen'd.
vreg_needed: Vec<bool>,
/// Next virtual register number to allocate.
next_vreg: u32,
/// Insts in reverse block order, before final copy to vcode.
block_insts: Vec<InstTuple<I>>,
/// Ranges in `block_insts` constituting BBs.
block_ranges: Vec<(usize, usize)>,
/// Instructions collected for the BB in progress, in reverse order, with
/// source-locs attached.
bb_insts: Vec<InstTuple<I>>,
/// Instructions collected for the CLIF inst in progress, in forward order.
ir_insts: Vec<InstTuple<I>>,
/// The register to use for GetPinnedReg, if any, on this architecture.
pinned_reg: Option<Reg>,
/// The vreg containing the special VmContext parameter, if it is present in the current
/// function's signature.
vm_context: Option<Reg>,
/// Notion of "relocation distance". This gives an estimate of how far away a symbol will be from a
/// reference.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum RelocDistance {
/// Target of relocation is "nearby". The threshold for this is fuzzy but should be interpreted
/// as approximately "within the compiled output of one module"; e.g., within AArch64's +/-
/// 128MB offset. If unsure, use `Far` instead.
/// Target of relocation could be anywhere in the address space.
fn alloc_vreg(
value_regs: &mut SecondaryMap<Value, Reg>,
regclass: RegClass,
value: Value,
next_vreg: &mut u32,
) -> VirtualReg {
if value_regs[value].is_invalid() {
// default value in map.
let v = *next_vreg;
*next_vreg += 1;
value_regs[value] = Reg::new_virtual(regclass, v);
debug!("value {} gets vreg {:?}", value, v);
enum GenerateReturn {
impl<'func, I: VCodeInst> Lower<'func, I> {
/// Prepare a new lowering context for the given IR function.
pub fn new(
f: &'func Function,
abi: Box<dyn ABICallee<I = I>>,
block_order: BlockLoweringOrder,
) -> CodegenResult<Lower<'func, I>> {
let mut vcode = VCodeBuilder::new(abi, block_order);
let mut next_vreg: u32 = 0;
let mut value_regs = SecondaryMap::with_default(Reg::invalid());
// Assign a vreg to each block param and each inst result.
for bb in f.layout.blocks() {
for &param in f.dfg.block_params(bb) {
let ty = f.dfg.value_type(param);
let vreg = alloc_vreg(&mut value_regs, I::rc_for_type(ty)?, param, &mut next_vreg);
vcode.set_vreg_type(vreg, ty);
debug!("bb {} param {}: vreg {:?}", bb, param, vreg);
for inst in f.layout.block_insts(bb) {
for &result in f.dfg.inst_results(inst) {
let ty = f.dfg.value_type(result);
let vreg =
alloc_vreg(&mut value_regs, I::rc_for_type(ty)?, result, &mut next_vreg);
vcode.set_vreg_type(vreg, ty);
"bb {} inst {} ({:?}): result vreg {:?}",
bb, inst, f.dfg[inst], vreg
let vm_context = f
.map(|vm_context_index| {
let entry_block = f.layout.entry_block().unwrap();
let param = f.dfg.block_params(entry_block)[vm_context_index];
// Assign a vreg to each return value.
let mut retval_regs = vec![];
for ret in &f.signature.returns {
let v = next_vreg;
next_vreg += 1;
let regclass = I::rc_for_type(ret.value_type)?;
let vreg = Reg::new_virtual(regclass, v);
vcode.set_vreg_type(vreg.as_virtual_reg().unwrap(), ret.value_type);
// Compute instruction colors, find constant instructions, and find instructions with
// side-effects, in one combined pass.
let mut cur_color = 0;
let mut inst_colors = SecondaryMap::with_default(InstColor::new(0));
let mut inst_constants = FxHashMap::default();
let mut inst_needed = SecondaryMap::with_default(false);
for bb in f.layout.blocks() {
cur_color += 1;
for inst in f.layout.block_insts(bb) {
let side_effect = has_lowering_side_effect(f, inst);
// Assign colors. A new color is chosen *after* any side-effecting instruction.
inst_colors[inst] = InstColor::new(cur_color);
debug!("bb {} inst {} has color {}", bb, inst, cur_color);
if side_effect {
debug!(" -> side-effecting");
inst_needed[inst] = true;
cur_color += 1;
// Determine if this is a constant; if so, add to the table.
if let Some(c) = is_constant_64bit(f, inst) {
debug!(" -> constant: {}", c);
inst_constants.insert(inst, c);
let vreg_needed = std::iter::repeat(false).take(next_vreg as usize).collect();
Ok(Lower {
block_insts: vec![],
block_ranges: vec![],
bb_insts: vec![],
ir_insts: vec![],
pinned_reg: None,
fn gen_arg_setup(&mut self) {
if let Some(entry_bb) = self.f.layout.entry_block() {
"gen_arg_setup: entry BB {} args are:\n{:?}",
for (i, param) in self.f.dfg.block_params(entry_bb).iter().enumerate() {
let reg = Writable::from_reg(self.value_regs[*param]);
let insn = self.vcode.abi().gen_copy_arg_to_reg(i, reg);
if let Some(insn) = self.vcode.abi().gen_retval_area_setup() {
fn gen_retval_setup(&mut self, gen_ret_inst: GenerateReturn) {
let retval_regs = self.retval_regs.clone();
for (i, reg) in retval_regs.into_iter().enumerate() {
let reg = Writable::from_reg(reg);
let insns = self.vcode.abi().gen_copy_reg_to_retval(i, reg);
for insn in insns {
let inst = match gen_ret_inst {
GenerateReturn::Yes => self.vcode.abi().gen_ret(),
GenerateReturn::No => self.vcode.abi().gen_epilogue_placeholder(),
fn lower_edge(&mut self, pred: Block, inst: Inst, succ: Block) -> CodegenResult<()> {
debug!("lower_edge: pred {} succ {}", pred, succ);
let num_args = self.f.dfg.block_params(succ).len();
debug_assert!(num_args == self.f.dfg.inst_variable_args(inst).len());
// Most blocks have no params, so skip all the hoop-jumping below and make an early exit.
if num_args == 0 {
return Ok(());
// Make up two vectors of info:
// * one for dsts which are to be assigned constants. We'll deal with those second, so
// as to minimise live ranges.
// * one for dsts whose sources are non-constants.
let mut const_bundles = SmallVec::<[(Type, Writable<Reg>, u64); 16]>::new();
let mut var_bundles = SmallVec::<[(Type, Writable<Reg>, Reg); 16]>::new();
let mut i = 0;
for (dst_val, src_val) in self
let src_val = self.f.dfg.resolve_aliases(*src_val);
let ty = self.f.dfg.value_type(src_val);
debug_assert!(ty == self.f.dfg.value_type(*dst_val));
let dst_reg = self.value_regs[*dst_val];
let input = self.get_input_for_val(inst, src_val);
debug!("jump arg {} is {}, reg {:?}", i, src_val, input.reg);
i += 1;
if let Some(c) = input.constant {
const_bundles.push((ty, Writable::from_reg(dst_reg), c));
} else {
let src_reg = input.reg;
// Skip self-assignments. Not only are they pointless, they falsely trigger the
// overlap-check below and hence can cause a lot of unnecessary copying through
// temporaries.
if dst_reg != src_reg {
var_bundles.push((ty, Writable::from_reg(dst_reg), src_reg));
// Deal first with the moves whose sources are variables.
// FIXME: use' SparseSetU here. This would avoid all heap allocation
// for cases of up to circa 16 args. Currently not possible because
// does not export it.
let mut src_reg_set = FxHashSet::<Reg>::default();
for (_, _, src_reg) in &var_bundles {
let mut overlaps = false;
for (_, dst_reg, _) in &var_bundles {
if src_reg_set.contains(&dst_reg.to_reg()) {
overlaps = true;
// If, as is mostly the case, the source and destination register sets are non
// overlapping, then we can copy directly, so as to save the register allocator work.
if !overlaps {
for (ty, dst_reg, src_reg) in &var_bundles {
self.emit(I::gen_move(*dst_reg, *src_reg, *ty));
} else {
// There's some overlap, so play safe and copy via temps.
let mut tmp_regs = SmallVec::<[Writable<Reg>; 16]>::new();
for (ty, _, _) in &var_bundles {
tmp_regs.push(self.alloc_tmp(I::rc_for_type(*ty)?, *ty));
for ((ty, _, src_reg), tmp_reg) in var_bundles.iter().zip(tmp_regs.iter()) {
self.emit(I::gen_move(*tmp_reg, *src_reg, *ty));
for ((ty, dst_reg, _), tmp_reg) in var_bundles.iter().zip(tmp_regs.iter()) {
self.emit(I::gen_move(*dst_reg, (*tmp_reg).to_reg(), *ty));
// Now, finally, deal with the moves whose sources are constants.
for (ty, dst_reg, const_u64) in &const_bundles {
for inst in I::gen_constant(*dst_reg, *const_u64, *ty, |reg_class, ty| {
self.alloc_tmp(reg_class, ty)
fn lower_clif_block<B: LowerBackend<MInst = I>>(
&mut self,
backend: &B,
block: Block,
) -> CodegenResult<()> {
// Lowering loop:
// - For each non-branch instruction, in reverse order:
// - If side-effecting (load, store, branch/call/return, possible trap), or if
// used outside of this block, or if demanded by another inst, then lower.
// That's it! Lowering of side-effecting ops will force all *needed*
// (live) non-side-effecting ops to be lowered at the right places, via
// the `use_input_reg()` callback on the `LowerCtx` (that's us). That's
// because `use_input_reg()` sets the eager/demand bit for any insts
// whose result registers are used.
// We build up the BB in reverse instruction order in `bb_insts`.
// Because the machine backend calls `ctx.emit()` in forward order, we
// collect per-IR-inst lowered instructions in `ir_insts`, then reverse
// these and append to `bb_insts` as we go backward through the block.
// `bb_insts` are then reversed again and appended to the VCode at the
// end of the BB (in the toplevel driver `lower()`).
for inst in self.f.layout.block_insts(block).rev() {
let data = &self.f.dfg[inst];
let value_needed = self
.any(|&result| self.vreg_needed[self.value_regs[result].get_index()]);
"lower_clif_block: block {} inst {} ({:?}) is_branch {} inst_needed {} value_needed {}",
if self.f.dfg[inst].opcode().is_branch() {
// Normal instruction: codegen if eager bit is set. (Other instructions may also be
// codegened if not eager when they are used by another instruction.)
if self.inst_needed[inst] || value_needed {
debug!("lowering: inst {}: {:?}", inst, self.f.dfg[inst]);
backend.lower(self, inst)?;
if data.opcode().is_return() {
// Return: handle specially, using ABI-appropriate sequence.
let gen_ret = if data.opcode() == Opcode::Return {
} else {
debug_assert!(data.opcode() == Opcode::FallthroughReturn);
let loc = self.srcloc(inst);
fn finish_ir_inst(&mut self, loc: SourceLoc) {
// `bb_insts` is kept in reverse order, so emit the instructions in
// reverse order.
for mut tuple in self.ir_insts.drain(..).rev() {
tuple.loc = loc;
fn finish_bb(&mut self) {
let start = self.block_insts.len();
for tuple in self.bb_insts.drain(..).rev() {
let end = self.block_insts.len();
self.block_ranges.push((start, end));
fn copy_bbs_to_vcode(&mut self) {
for &(start, end) in self.block_ranges.iter().rev() {
for &InstTuple {
ref inst,
} in &self.block_insts[start..end]
self.vcode.push(inst.clone(), is_safepoint);
fn lower_clif_branches<B: LowerBackend<MInst = I>>(
&mut self,
backend: &B,
block: Block,
branches: &SmallVec<[Inst; 2]>,
targets: &SmallVec<[MachLabel; 2]>,
maybe_fallthrough: Option<MachLabel>,
) -> CodegenResult<()> {
"lower_clif_branches: block {} branches {:?} targets {:?} maybe_fallthrough {:?}",
block, branches, targets, maybe_fallthrough
backend.lower_branch_group(self, branches, targets, maybe_fallthrough)?;
let loc = self.srcloc(branches[0]);
fn collect_branches_and_targets(
bindex: BlockIndex,
_bb: Block,
branches: &mut SmallVec<[Inst; 2]>,
targets: &mut SmallVec<[MachLabel; 2]>,
) {
let mut last_inst = None;
for &(inst, succ) in self.vcode.block_order().succ_indices(bindex) {
// Avoid duplicates: this ensures a br_table is only inserted once.
if last_inst != Some(inst) {
} else {
debug_assert!(self.f.dfg[inst].opcode() == Opcode::BrTable);
debug_assert!(branches.len() == 1);
last_inst = Some(inst);
/// Lower the function.
pub fn lower<B: LowerBackend<MInst = I>>(
mut self,
backend: &B,
) -> CodegenResult<(VCode<I>, StackmapRequestInfo)> {
debug!("about to lower function: {:?}", self.f);
// Initialize the ABI object, giving it a temp if requested.
let maybe_tmp = if self.vcode.abi().temp_needed() {
Some(self.alloc_tmp(RegClass::I64, I64))
} else {
// Get the pinned reg here (we only parameterize this function on `B`,
// not the whole `Lower` impl).
self.pinned_reg = backend.maybe_pinned_reg();
// Reused vectors for branch lowering.
let mut branches: SmallVec<[Inst; 2]> = SmallVec::new();
let mut targets: SmallVec<[MachLabel; 2]> = SmallVec::new();
// get a copy of the lowered order; we hold this separately because we
// need a mut ref to the vcode to mutate it below.
let lowered_order: SmallVec<[LoweredBlock; 64]> = self
// Main lowering loop over lowered blocks.
for (bindex, lb) in lowered_order.iter().enumerate().rev() {
let bindex = bindex as BlockIndex;
// Lower the block body in reverse order (see comment in
// `lower_clif_block()` for rationale).
// End branches.
if let Some(bb) = lb.orig_block() {
self.collect_branches_and_targets(bindex, bb, &mut branches, &mut targets);
if branches.len() > 0 {
let maybe_fallthrough = if (bindex + 1) < (lowered_order.len() as BlockIndex) {
Some(MachLabel::from_block(bindex + 1))
} else {
self.lower_clif_branches(backend, bb, &branches, &targets, maybe_fallthrough)?;
} else {
// If no orig block, this must be a pure edge block; get the successor and
// emit a jump.
let (_, succ) = self.vcode.block_order().succ_indices(bindex)[0];
// Out-edge phi moves.
if let Some((pred, inst, succ)) = lb.out_edge() {
self.lower_edge(pred, inst, succ)?;
// Original block body.
if let Some(bb) = lb.orig_block() {
self.lower_clif_block(backend, bb)?;
// In-edge phi moves.
if let Some((pred, inst, succ)) = lb.in_edge() {
self.lower_edge(pred, inst, succ)?;
if bindex == 0 {
// Set up the function with arg vreg inits.
// Now that we've emitted all instructions into the VCodeBuilder, let's build the VCode.
let (vcode, stack_map_info) =;
debug!("built vcode: {:?}", vcode);
Ok((vcode, stack_map_info))
/// Get the actual inputs for a value. This is the implementation for
/// `get_input()` but starting from the SSA value, which is not exposed to
/// the backend.
fn get_input_for_val(&self, at_inst: Inst, val: Value) -> LowerInput {
debug!("get_input_for_val: val {} at inst {}", val, at_inst);
let mut reg = self.value_regs[val];
debug!(" -> reg {:?}", reg);
let mut inst = match self.f.dfg.value_def(val) {
// OK to merge source instruction if (i) we have a source
// instruction, and either (ii-a) it has no side effects, or (ii-b)
// it has the same color as this instruction.
ValueDef::Result(src_inst, result_idx) => {
debug!(" -> src inst {}", src_inst);
" -> has lowering side effect: {}",
has_lowering_side_effect(self.f, src_inst)
" -> our color is {:?}, src inst is {:?}",
if !has_lowering_side_effect(self.f, src_inst)
|| self.inst_color(at_inst) == self.inst_color(src_inst)
Some((src_inst, result_idx))
} else {
_ => None,
let constant = inst.and_then(|(inst, _)| self.get_constant(inst));
// Pinned-reg hack: if backend specifies a fixed pinned register, use it
// directly when we encounter a GetPinnedReg op, rather than lowering
// the actual op, and do not return the source inst to the caller; the
// value comes "out of the ether" and we will not force generation of
// the superfluous move.
if let Some((i, _)) = inst {
if self.f.dfg[i].opcode() == Opcode::GetPinnedReg {
if let Some(pr) = self.pinned_reg {
reg = pr;
inst = None;
LowerInput {
impl<'func, I: VCodeInst> LowerCtx for Lower<'func, I> {
type I = I;
fn abi(&mut self) -> &dyn ABICallee<I = I> {
fn retval(&self, idx: usize) -> Writable<Reg> {
fn get_vm_context(&self) -> Option<Reg> {
fn data(&self, ir_inst: Inst) -> &InstructionData {
fn ty(&self, ir_inst: Inst) -> Type {
fn call_target<'b>(&'b self, ir_inst: Inst) -> Option<(&'b ExternalName, RelocDistance)> {
match &self.f.dfg[ir_inst] {
&InstructionData::Call { func_ref, .. }
| &InstructionData::FuncAddr { func_ref, .. } => {
let funcdata = &self.f.dfg.ext_funcs[func_ref];
let dist = funcdata.reloc_distance();
Some((&, dist))
_ => None,
fn call_sig<'b>(&'b self, ir_inst: Inst) -> Option<&'b Signature> {
match &self.f.dfg[ir_inst] {
&InstructionData::Call { func_ref, .. } => {
let funcdata = &self.f.dfg.ext_funcs[func_ref];
&InstructionData::CallIndirect { sig_ref, .. } => Some(&self.f.dfg.signatures[sig_ref]),
_ => None,
fn symbol_value<'b>(&'b self, ir_inst: Inst) -> Option<(&'b ExternalName, RelocDistance, i64)> {
match &self.f.dfg[ir_inst] {
&InstructionData::UnaryGlobalValue { global_value, .. } => {
let gvdata = &self.f.global_values[global_value];
match gvdata {
&GlobalValueData::Symbol {
ref name,
ref offset,
} => {
let offset = offset.bits();
let dist = gvdata.maybe_reloc_distance().unwrap();
Some((name, dist, offset))
_ => None,
_ => None,
fn memflags(&self, ir_inst: Inst) -> Option<MemFlags> {
match &self.f.dfg[ir_inst] {
&InstructionData::AtomicCas { flags, .. } => Some(flags),
&InstructionData::AtomicRmw { flags, .. } => Some(flags),
&InstructionData::Load { flags, .. }
| &InstructionData::LoadComplex { flags, .. }
| &InstructionData::LoadNoOffset { flags, .. }
| &InstructionData::Store { flags, .. }
| &InstructionData::StoreComplex { flags, .. } => Some(flags),
&InstructionData::StoreNoOffset { flags, .. } => Some(flags),
_ => None,
fn srcloc(&self, ir_inst: Inst) -> SourceLoc {
fn inst_color(&self, ir_inst: Inst) -> InstColor {
fn num_inputs(&self, ir_inst: Inst) -> usize {
fn num_outputs(&self, ir_inst: Inst) -> usize {
fn input_ty(&self, ir_inst: Inst, idx: usize) -> Type {
let val = self.f.dfg.inst_args(ir_inst)[idx];
let val = self.f.dfg.resolve_aliases(val);
fn output_ty(&self, ir_inst: Inst, idx: usize) -> Type {
fn get_constant(&self, ir_inst: Inst) -> Option<u64> {
fn get_input(&self, ir_inst: Inst, idx: usize) -> LowerInput {
let val = self.f.dfg.inst_args(ir_inst)[idx];
let val = self.f.dfg.resolve_aliases(val);
self.get_input_for_val(ir_inst, val)
fn get_output(&self, ir_inst: Inst, idx: usize) -> Writable<Reg> {
let val = self.f.dfg.inst_results(ir_inst)[idx];
fn alloc_tmp(&mut self, rc: RegClass, ty: Type) -> Writable<Reg> {
let v = self.next_vreg;
self.next_vreg += 1;
let vreg = Reg::new_virtual(rc, v);
self.vcode.set_vreg_type(vreg.as_virtual_reg().unwrap(), ty);
fn emit(&mut self, mach_inst: I) {
self.ir_insts.push(InstTuple {
loc: SourceLoc::default(),
is_safepoint: false,
inst: mach_inst,
fn emit_safepoint(&mut self, mach_inst: I) {
self.ir_insts.push(InstTuple {
loc: SourceLoc::default(),
is_safepoint: true,
inst: mach_inst,
fn use_input_reg(&mut self, input: LowerInput) {
debug!("use_input_reg: vreg {:?} is needed", input.reg);
// We may directly return a real (machine) register when we know that register holds the
// result of an opcode (e.g. GetPinnedReg).
if input.reg.is_virtual() {
self.vreg_needed[input.reg.get_index()] = true;
fn is_reg_needed(&self, ir_inst: Inst, reg: Reg) -> bool {
self.inst_needed[ir_inst] || self.vreg_needed[reg.get_index()]
fn get_constant_data(&self, constant_handle: Constant) -> &ConstantData {
fn get_immediate(&self, imm: Immediate) -> &ConstantData {
fn ensure_in_vreg(&mut self, reg: Reg, ty: Type) -> Reg {
if reg.is_virtual() {
} else {
let rc = reg.get_class();
let new_reg = self.alloc_tmp(rc, ty);
self.emit(I::gen_move(new_reg, reg, ty));
/// Visit all successors of a block with a given visitor closure.
pub(crate) fn visit_block_succs<F: FnMut(Inst, Block)>(f: &Function, block: Block, mut visit: F) {
for inst in f.layout.block_likely_branches(block) {
if f.dfg[inst].opcode().is_branch() {
visit_branch_targets(f, block, inst, &mut visit);
fn visit_branch_targets<F: FnMut(Inst, Block)>(
f: &Function,
block: Block,
inst: Inst,
visit: &mut F,
) {
if f.dfg[inst].opcode() == Opcode::Fallthrough {
visit(inst, f.layout.next_block(block).unwrap());
} else {
match f.dfg[inst].analyze_branch(&f.dfg.value_lists) {
BranchInfo::NotABranch => {}
BranchInfo::SingleDest(dest, _) => {
visit(inst, dest);
BranchInfo::Table(table, maybe_dest) => {
if let Some(dest) = maybe_dest {
visit(inst, dest);
for &dest in f.jump_tables[table].as_slice() {
visit(inst, dest);