334 lines
12 KiB
Rust
334 lines
12 KiB
Rust
//! WebAssembly function translation state.
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//!
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//! The `TranslationState` struct defined in this module is used to keep track of the WebAssembly
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//! value and control stacks during the translation of a single function.
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use cretonne::ir::{self, Ebb, Inst, Value};
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use environ::{FuncEnvironment, GlobalValue};
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use std::collections::HashMap;
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use translation_utils::{GlobalIndex, MemoryIndex, SignatureIndex, FunctionIndex};
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/// A control stack frame can be an `if`, a `block` or a `loop`, each one having the following
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/// fields:
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///
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/// - `destination`: reference to the `Ebb` that will hold the code after the control block;
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/// - `num_return_values`: number of values returned by the control block;
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/// - `original_stack_size`: size of the value stack at the beginning of the control block.
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///
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/// Moreover, the `if` frame has the `branch_inst` field that points to the `brz` instruction
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/// separating the `true` and `false` branch. The `loop` frame has a `header` field that references
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/// the `Ebb` that contains the beginning of the body of the loop.
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#[derive(Debug)]
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pub enum ControlStackFrame {
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If {
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destination: Ebb,
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branch_inst: Inst,
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num_return_values: usize,
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original_stack_size: usize,
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reachable: bool,
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},
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Block {
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destination: Ebb,
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num_return_values: usize,
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original_stack_size: usize,
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reachable: bool,
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},
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Loop {
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destination: Ebb,
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header: Ebb,
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num_return_values: usize,
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original_stack_size: usize,
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reachable: bool,
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},
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}
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/// Helper methods for the control stack objects.
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impl ControlStackFrame {
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pub fn num_return_values(&self) -> usize {
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match *self {
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ControlStackFrame::If { num_return_values, .. } |
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ControlStackFrame::Block { num_return_values, .. } |
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ControlStackFrame::Loop { num_return_values, .. } => num_return_values,
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}
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}
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pub fn following_code(&self) -> Ebb {
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match *self {
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ControlStackFrame::If { destination, .. } |
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ControlStackFrame::Block { destination, .. } |
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ControlStackFrame::Loop { destination, .. } => destination,
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}
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}
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pub fn br_destination(&self) -> Ebb {
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match *self {
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ControlStackFrame::If { destination, .. } |
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ControlStackFrame::Block { destination, .. } => destination,
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ControlStackFrame::Loop { header, .. } => header,
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}
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}
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pub fn original_stack_size(&self) -> usize {
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match *self {
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ControlStackFrame::If { original_stack_size, .. } |
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ControlStackFrame::Block { original_stack_size, .. } |
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ControlStackFrame::Loop { original_stack_size, .. } => original_stack_size,
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}
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}
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pub fn is_loop(&self) -> bool {
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match *self {
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ControlStackFrame::If { .. } |
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ControlStackFrame::Block { .. } => false,
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ControlStackFrame::Loop { .. } => true,
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}
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}
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pub fn is_reachable(&self) -> bool {
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match *self {
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ControlStackFrame::If { reachable, .. } |
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ControlStackFrame::Block { reachable, .. } |
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ControlStackFrame::Loop { reachable, .. } => reachable,
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}
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}
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pub fn set_reachable(&mut self) {
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match *self {
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ControlStackFrame::If { ref mut reachable, .. } |
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ControlStackFrame::Block { ref mut reachable, .. } |
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ControlStackFrame::Loop { ref mut reachable, .. } => *reachable = true,
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}
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}
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}
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/// Contains information passed along during the translation and that records:
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///
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/// - The current value and control stacks.
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/// - The depth of the two unreachable control blocks stacks, that are manipulated when translating
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/// unreachable code;
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pub struct TranslationState {
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pub stack: Vec<Value>,
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pub control_stack: Vec<ControlStackFrame>,
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pub phantom_unreachable_stack_depth: usize,
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pub real_unreachable_stack_depth: usize,
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// Map of global variables that have already been created by `FuncEnvironment::make_global`.
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globals: HashMap<GlobalIndex, GlobalValue>,
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// Map of heaps that have been created by `FuncEnvironment::make_heap`.
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heaps: HashMap<MemoryIndex, ir::Heap>,
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// Map of indirect call signatures that have been created by
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// `FuncEnvironment::make_indirect_sig()`.
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// Stores both the signature reference and the number of WebAssembly arguments
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signatures: HashMap<SignatureIndex, (ir::SigRef, usize)>,
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// Imported and local functions that have been created by
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// `FuncEnvironment::make_direct_func()`.
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// Stores both the function reference and the number of WebAssembly arguments
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functions: HashMap<FunctionIndex, (ir::FuncRef, usize)>,
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}
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impl TranslationState {
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pub fn new() -> TranslationState {
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TranslationState {
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stack: Vec::new(),
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control_stack: Vec::new(),
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phantom_unreachable_stack_depth: 0,
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real_unreachable_stack_depth: 0,
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globals: HashMap::new(),
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heaps: HashMap::new(),
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signatures: HashMap::new(),
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functions: HashMap::new(),
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}
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}
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fn clear(&mut self) {
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debug_assert!(self.stack.is_empty());
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debug_assert!(self.control_stack.is_empty());
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debug_assert_eq!(self.phantom_unreachable_stack_depth, 0);
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debug_assert_eq!(self.real_unreachable_stack_depth, 0);
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self.globals.clear();
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self.heaps.clear();
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self.signatures.clear();
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self.functions.clear();
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}
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/// Initialize the state for compiling a function with the given signature.
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///
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/// This resets the state to containing only a single block representing the whole function.
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/// The exit block is the last block in the function which will contain the return instruction.
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pub fn initialize(&mut self, sig: &ir::Signature, exit_block: Ebb) {
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self.clear();
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self.push_block(
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exit_block,
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sig.returns
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.iter()
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.filter(|arg| arg.purpose == ir::ArgumentPurpose::Normal)
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.count(),
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);
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}
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/// Push a value.
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pub fn push1(&mut self, val: Value) {
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self.stack.push(val);
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}
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/// Push multiple values.
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pub fn pushn(&mut self, vals: &[Value]) {
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self.stack.extend_from_slice(vals);
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}
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/// Pop one value.
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pub fn pop1(&mut self) -> Value {
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self.stack.pop().unwrap()
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}
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/// Peek at the top of the stack without popping it.
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pub fn peek1(&self) -> Value {
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*self.stack.last().unwrap()
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}
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/// Pop two values. Return them in the order they were pushed.
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pub fn pop2(&mut self) -> (Value, Value) {
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let v2 = self.stack.pop().unwrap();
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let v1 = self.stack.pop().unwrap();
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(v1, v2)
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}
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/// Pop three values. Return them in the order they were pushed.
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pub fn pop3(&mut self) -> (Value, Value, Value) {
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let v3 = self.stack.pop().unwrap();
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let v2 = self.stack.pop().unwrap();
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let v1 = self.stack.pop().unwrap();
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(v1, v2, v3)
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}
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/// Pop the top `n` values on the stack.
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///
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/// The popped values are not returned. Use `peekn` to look at them before popping.
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pub fn popn(&mut self, n: usize) {
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let new_len = self.stack.len() - n;
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self.stack.truncate(new_len);
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}
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/// Peek at the top `n` values on the stack in the order they were pushed.
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pub fn peekn(&self, n: usize) -> &[Value] {
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&self.stack[self.stack.len() - n..]
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}
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// Push a block on the control stack.
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pub fn push_block(&mut self, following_code: Ebb, num_result_types: usize) {
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self.control_stack.push(ControlStackFrame::Block {
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destination: following_code,
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original_stack_size: self.stack.len(),
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num_return_values: num_result_types,
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reachable: false,
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});
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}
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// Push a loop on the control stack.
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pub fn push_loop(&mut self, header: Ebb, following_code: Ebb, num_result_types: usize) {
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self.control_stack.push(ControlStackFrame::Loop {
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header,
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destination: following_code,
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original_stack_size: self.stack.len(),
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num_return_values: num_result_types,
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reachable: false,
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});
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}
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// Push an if on the control stack.
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pub fn push_if(&mut self, branch_inst: Inst, following_code: Ebb, num_result_types: usize) {
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self.control_stack.push(ControlStackFrame::If {
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branch_inst,
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destination: following_code,
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original_stack_size: self.stack.len(),
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num_return_values: num_result_types,
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reachable: false,
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});
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}
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/// Test if the translation state is currently in unreachable code.
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pub fn in_unreachable_code(&self) -> bool {
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if self.real_unreachable_stack_depth > 0 {
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true
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} else {
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debug_assert_eq!(self.phantom_unreachable_stack_depth, 0, "in reachable code");
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false
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}
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}
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}
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/// Methods for handling entity references.
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impl TranslationState {
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/// Get the `GlobalVar` reference that should be used to access the global variable `index`.
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/// Create the reference if necessary.
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/// Also return the WebAssembly type of the global.
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pub fn get_global<FE: FuncEnvironment + ?Sized>(
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&mut self,
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func: &mut ir::Function,
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index: u32,
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environ: &mut FE,
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) -> GlobalValue {
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let index = index as GlobalIndex;
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*self.globals.entry(index).or_insert_with(
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|| environ.make_global(func, index),
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)
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}
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/// Get the `Heap` reference that should be used to access linear memory `index`.
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/// Create the reference if necessary.
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pub fn get_heap<FE: FuncEnvironment + ?Sized>(
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&mut self,
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func: &mut ir::Function,
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index: u32,
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environ: &mut FE,
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) -> ir::Heap {
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let index = index as MemoryIndex;
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*self.heaps.entry(index).or_insert_with(
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|| environ.make_heap(func, index),
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)
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}
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/// Get the `SigRef` reference that should be used to make an indirect call with signature
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/// `index`. Also return the number of WebAssembly arguments in the signature.
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///
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/// Create the signature if necessary.
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pub fn get_indirect_sig<FE: FuncEnvironment + ?Sized>(
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&mut self,
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func: &mut ir::Function,
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index: u32,
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environ: &mut FE,
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) -> (ir::SigRef, usize) {
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let index = index as SignatureIndex;
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*self.signatures.entry(index).or_insert_with(|| {
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let sig = environ.make_indirect_sig(func, index);
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(sig, normal_args(&func.dfg.signatures[sig]))
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})
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}
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/// Get the `FuncRef` reference that should be used to make a direct call to function
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/// `index`. Also return the number of WebAssembly arguments in the signature.
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///
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/// Create the function reference if necessary.
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pub fn get_direct_func<FE: FuncEnvironment + ?Sized>(
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&mut self,
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func: &mut ir::Function,
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index: u32,
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environ: &mut FE,
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) -> (ir::FuncRef, usize) {
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let index = index as FunctionIndex;
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*self.functions.entry(index).or_insert_with(|| {
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let fref = environ.make_direct_func(func, index);
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let sig = func.dfg.ext_funcs[fref].signature;
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(fref, normal_args(&func.dfg.signatures[sig]))
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})
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}
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}
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/// Count the number of normal parameters in a signature.
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/// Exclude special-purpose parameters that represent runtime stuff and not WebAssembly arguments.
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fn normal_args(sig: &ir::Signature) -> usize {
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sig.params
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.iter()
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.filter(|arg| arg.purpose == ir::ArgumentPurpose::Normal)
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.count()
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}
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