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Remove the concept of non-dense jump tables.

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WebAssembly doesn't have non-dense jump tables, and higher-level users
are better served by the facilities in lib/frontend/src/switch.rs for
working with non-dense switches.

This eliminates the concept of "absent" jump table entries, which
were represented as "0" in the text format.

Also, jump table contents are now enclosed in `[` and `]`, so that
we can unambiguously display empty jump tables. Previously, empty jump
tables were displayed as if they had a single absent entry.
This commit is contained in:
Dan Gohman
2018-10-04 10:35:31 -07:00
parent dc9221a70c
commit 1098eafb45
22 changed files with 113 additions and 208 deletions
Download Patch File Download Diff File Expand all files Collapse all files

140
lib/codegen/src/ir/jumptable.rs
View File

@@ -4,39 +4,29 @@
//! The actual table of destinations is stored in a `JumpTableData` struct defined in this module.
use ir::entities::Ebb;
use packed_option::PackedOption;
use std::fmt::{self, Display, Formatter};
use std::iter;
use std::slice;
use std::slice::{Iter, IterMut};
use std::vec::Vec;
/// Contents of a jump table.
///
/// All jump tables use 0-based indexing and are expected to be densely populated. They don't need
/// to be completely populated, though. Individual entries can be missing.
/// All jump tables use 0-based indexing and densely populated.
#[derive(Clone)]
pub struct JumpTableData {
// Table entries, using `None` as a placeholder for missing entries.
table: Vec<PackedOption<Ebb>>,
// How many `None` holes in table?
holes: usize,
// Table entries.
table: Vec<Ebb>,
}
impl JumpTableData {
/// Create a new empty jump table.
pub fn new() -> Self {
Self {
table: Vec::new(),
holes: 0,
}
Self { table: Vec::new() }
}
/// Create a new empty jump table with the specified capacity.
pub fn with_capacity(capacity: usize) -> Self {
Self {
table: Vec::with_capacity(capacity),
holes: 0,
}
}
@@ -45,100 +35,48 @@ impl JumpTableData {
self.table.len()
}
/// Boolean that is false if the table has missing entries.
pub fn fully_dense(&self) -> bool {
self.holes == 0
}
/// Set a table entry.
///
/// The table will grow as needed to fit `idx`.
pub fn set_entry(&mut self, idx: usize, dest: Ebb) {
// Resize table to fit `idx`.
if idx >= self.table.len() {
self.holes += idx - self.table.len();
self.table.resize(idx + 1, None.into());
} else if self.table[idx].is_none() {
// We're filling in an existing hole.
self.holes -= 1;
}
self.table[idx] = dest.into();
}
/// Append a table entry.
pub fn push_entry(&mut self, dest: Ebb) {
self.table.push(dest.into())
}
/// Clear a table entry.
///
/// The `br_table` instruction will fall through if given an index corresponding to a cleared
/// table entry.
pub fn clear_entry(&mut self, idx: usize) {
if idx < self.table.len() && self.table[idx].is_some() {
self.holes += 1;
self.table[idx] = None.into();
}
}
/// Get the entry for `idx`, or `None`.
pub fn get_entry(&self, idx: usize) -> Option<Ebb> {
self.table.get(idx).and_then(|e| e.expand())
}
/// Enumerate over all `(idx, dest)` pairs in the table in order.
///
/// This returns an iterator that skips any empty slots in the table.
pub fn entries(&self) -> Entries {
Entries(self.table.iter().cloned().enumerate())
self.table.push(dest)
}
/// Checks if any of the entries branch to `ebb`.
pub fn branches_to(&self, ebb: Ebb) -> bool {
self.table
.iter()
.any(|target_ebb| target_ebb.expand() == Some(ebb))
self.table.iter().any(|target_ebb| *target_ebb == ebb)
}
/// Access the whole table as a slice.
pub fn as_slice(&self) -> &[Ebb] {
self.table.as_slice()
}
/// Access the whole table as a mutable slice.
pub fn as_mut_slice(&mut self) -> &mut [PackedOption<Ebb>] {
pub fn as_mut_slice(&mut self) -> &mut [Ebb] {
self.table.as_mut_slice()
}
}
/// Enumerate `(idx, dest)` pairs in order.
pub struct Entries<'a>(iter::Enumerate<iter::Cloned<slice::Iter<'a, PackedOption<Ebb>>>>);
/// Returns an iterator over the table.
pub fn iter(&self) -> Iter<Ebb> {
self.table.iter()
}
impl<'a> Iterator for Entries<'a> {
type Item = (usize, Ebb);
fn next(&mut self) -> Option<Self::Item> {
loop {
if let Some((idx, dest)) = self.0.next() {
if let Some(ebb) = dest.expand() {
return Some((idx, ebb));
}
} else {
return None;
}
}
/// Returns an iterator that allows modifying each value.
pub fn iter_mut(&mut self) -> IterMut<Ebb> {
self.table.iter_mut()
}
}
impl Display for JumpTableData {
fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
match self.table.first().and_then(|e| e.expand()) {
None => write!(fmt, "jump_table 0")?,
Some(first) => write!(fmt, "jump_table {}", first)?,
write!(fmt, "jump_table [")?;
match self.table.first() {
None => (),
Some(first) => write!(fmt, "{}", first)?,
}
for dest in self.table.iter().skip(1).map(|e| e.expand()) {
match dest {
None => write!(fmt, ", 0")?,
Some(ebb) => write!(fmt, ", {}", ebb)?,
}
for ebb in self.table.iter().skip(1) {
write!(fmt, ", {}", ebb)?;
}
Ok(())
write!(fmt, "]")
}
}
@@ -148,18 +86,17 @@ mod tests {
use entity::EntityRef;
use ir::Ebb;
use std::string::ToString;
use std::vec::Vec;
#[test]
fn empty() {
let jt = JumpTableData::new();
assert_eq!(jt.get_entry(0), None);
assert_eq!(jt.get_entry(10), None);
assert_eq!(jt.as_slice().get(0), None);
assert_eq!(jt.as_slice().get(10), None);
assert_eq!(jt.to_string(), "jump_table 0");
assert_eq!(jt.to_string(), "jump_table []");
let v: Vec<(usize, Ebb)> = jt.entries().collect();
let v = jt.as_slice();
assert_eq!(v, []);
}
@@ -170,16 +107,13 @@ mod tests {
let mut jt = JumpTableData::new();
jt.set_entry(0, e1);
jt.set_entry(0, e2);
jt.set_entry(10, e1);
jt.push_entry(e1);
jt.push_entry(e2);
jt.push_entry(e1);
assert_eq!(
jt.to_string(),
"jump_table ebb2, 0, 0, 0, 0, 0, 0, 0, 0, 0, ebb1"
);
assert_eq!(jt.to_string(), "jump_table [ebb1, ebb2, ebb1]");
let v: Vec<(usize, Ebb)> = jt.entries().collect();
assert_eq!(v, [(0, e2), (10, e1)]);
let v = jt.as_slice();
assert_eq!(v, [e1, e2, e1]);
}
}