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hashx: Simplify RegisterWriterMap 

I originally wrote this in an overcomplicated way, to avoid
frequent initialization of a RegisterWriter array. It turns out
that RegisterWriter can be fairly compact, so this extra level of
indirection isn't necessary or measurably helpful.

This still manages to avoid declaring RegisterWriter as Copy, by
using Default to initialize the array instead of an array constructor.

Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>
This commit is contained in:
Micah Elizabeth Scott 2023-07-19 16:23:25 -07:00
parent f4939a5fd8
commit 7579febb46
1 changed files with 5 additions and 28 deletions
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33
crates/hashx/src/constraints.rs
View File

@ -12,7 +12,6 @@
use crate::program::{Instruction, InstructionArray, Opcode};
use crate::register::{RegisterId, RegisterSet, NUM_REGISTERS};
use crate::scheduler::Scheduler;
use arrayvec::ArrayVec;
pub(crate) use model::{Pass, RegisterWriter};
@ -279,47 +278,25 @@ pub(crate) fn opcode_pair_allowed(previous: Option<Opcode>, proposed: Opcode) ->
}
/// Map each [`RegisterId`] to an [`Option<RegisterWriter>`]
#[derive(Debug, Clone)]
struct RegisterWriterMap {
/// Array of indices in the 'writers' array for each register
regs: [Option<u8>; NUM_REGISTERS],
/// Array of RegisterWriters, indexed by the content of 'regs'
writers: ArrayVec<RegisterWriter, NUM_REGISTERS>,
}
#[derive(Default, Debug, Clone)]
struct RegisterWriterMap([Option<RegisterWriter>; NUM_REGISTERS]);
impl RegisterWriterMap {
/// A new empty register writer map. All registers are set to None
#[inline(always)]
fn new() -> Self {
Self {
regs: [None; NUM_REGISTERS],
writers: Default::default(),
}
Default::default()
}
/// Write or overwrite the last [`RegisterWriter`] associated with `reg`
#[inline(always)]
fn insert(&mut self, reg: RegisterId, writer: RegisterWriter) {
let previous = self.regs[reg.as_usize()];
match previous {
None => {
let new_index = self.writers.len();
self.writers.push(writer);
self.regs[reg.as_usize()] = Some(
new_index
.try_into()
.expect("RegisterWriterMap always uses a wide enough data type"),
);
}
Some(update_index) => {
self.writers[update_index as usize] = writer;
}
}
self.0[reg.as_usize()] = Some(writer);
}
/// Return the most recent mapping for 'reg', if any
#[inline(always)]
fn get(&self, reg: RegisterId) -> Option<&RegisterWriter> {
self.regs[reg.as_usize()].map(|index| &self.writers[index as usize])
self.0[reg.as_usize()].as_ref()
}
}