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Implement register allocation (#3942)
* Implement register allocation * Apply review * Update core/engine/src/vm/opcode/rest_parameter/mod.rs Co-authored-by: raskad <[email protected]> --------- Co-authored-by: raskad <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,140 @@ | ||
| use std::mem::forget; | ||
|
|
||
| bitflags::bitflags! { | ||
| #[derive(Debug, Default, Clone, Copy)] | ||
| struct RegisterFlags: u8 { | ||
| /// Whether the register is still in use (not deallocated). | ||
| const USED = 0b0000_0001; | ||
|
|
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| /// Is the register presistent (not deallocatable). | ||
| const PERSISTENT = 0b0000_0010; | ||
| } | ||
| } | ||
|
|
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| impl RegisterFlags { | ||
| fn is_used(self) -> bool { | ||
| self.contains(Self::USED) | ||
| } | ||
| fn is_persistent(self) -> bool { | ||
| self.contains(Self::PERSISTENT) | ||
| } | ||
| } | ||
|
|
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| /// An entry in the [`RegisterAllocator`]. | ||
| #[derive(Debug, Default)] | ||
| pub(crate) struct RegisterEntry { | ||
| flags: RegisterFlags, | ||
| } | ||
|
|
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| /// Represent a VM register. | ||
| /// | ||
| /// This is intented to be passed by reference or to be moved, dropping this is a bug, | ||
| /// it should only be dropped though the [`RegisterAllocator::dealloc()`] method. | ||
| /// This doesn't apply to persistent registers. | ||
| /// | ||
| /// A [`Register`] is index into the register allocator, | ||
| /// as well as an index into the registers on the stack using the register pointer (`rp`). | ||
| #[derive(Debug)] | ||
| pub(crate) struct Register { | ||
| index: u32, | ||
| flags: RegisterFlags, | ||
| } | ||
|
|
||
| impl Register { | ||
| /// The index of the [`Register`]. | ||
| pub(crate) fn index(&self) -> u32 { | ||
| self.index | ||
| } | ||
| } | ||
|
|
||
| impl Drop for Register { | ||
| /// This method should never be called. | ||
| /// It is used to detect when a register has not been deallocated. | ||
| fn drop(&mut self) { | ||
| if self.flags.is_persistent() { | ||
| return; | ||
| } | ||
|
|
||
| // Prevent double panic. | ||
| if std::thread::panicking() { | ||
| return; | ||
| } | ||
|
|
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| unreachable!("forgot to deallocate a register!") | ||
| } | ||
| } | ||
|
|
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| #[derive(Debug, Default)] | ||
| pub(crate) struct RegisterAllocator { | ||
| registers: Vec<RegisterEntry>, | ||
| } | ||
|
|
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| impl RegisterAllocator { | ||
| pub(crate) fn alloc(&mut self) -> Register { | ||
| if let Some((i, register)) = self | ||
| .registers | ||
| .iter_mut() | ||
| .filter(|reg| !reg.flags.is_used()) | ||
| .enumerate() | ||
| .next() | ||
| { | ||
| assert!(!register.flags.is_persistent()); | ||
|
|
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| register.flags |= RegisterFlags::USED; | ||
| return Register { | ||
| index: i as u32, | ||
| flags: register.flags, | ||
| }; | ||
| } | ||
|
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| let flags = RegisterFlags::USED; | ||
|
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| let index = self.registers.len() as u32; | ||
| self.registers.push(RegisterEntry { flags }); | ||
|
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| Register { index, flags } | ||
| } | ||
|
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| pub(crate) fn alloc_persistent(&mut self) -> Register { | ||
| let mut reg = self.alloc(); | ||
|
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| let index = reg.index(); | ||
|
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| let register = &mut self.registers[index as usize]; | ||
|
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| register.flags |= RegisterFlags::PERSISTENT; | ||
|
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| reg.flags = register.flags; | ||
| reg | ||
| } | ||
|
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| #[allow(unused)] | ||
| pub(crate) fn dealloc(&mut self, reg: Register) { | ||
| assert!( | ||
| !reg.flags.is_persistent(), | ||
| "Trying to deallocate a persistent register" | ||
| ); | ||
|
|
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| let register = &mut self.registers[reg.index as usize]; | ||
|
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| assert!( | ||
| register.flags.is_used(), | ||
| "Cannot deallocate unused variable" | ||
| ); | ||
| register.flags.set(RegisterFlags::USED, false); | ||
|
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| // NOTE: We should not drop it since, dropping it used to detect bugs. | ||
| forget(reg); | ||
| } | ||
|
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| pub(crate) fn finish(self) -> u32 { | ||
| for register in &self.registers { | ||
| debug_assert!( | ||
| !register.flags.is_used() | ||
| || (register.flags.is_used() && register.flags.is_persistent()) | ||
| ); | ||
| } | ||
|
|
||
| self.registers.len() as u32 | ||
| } | ||
| } |
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