Remove RegisterBufCache since it didn't really measurably help at all

crates/nu-engine/src/eval_ir.rs

@@ -24,7 +24,12 @@ pub fn eval_ir_block<D: DebugContext>(
 
         let args_base = stack.arguments.get_base();
         let error_handler_base = stack.error_handlers.get_base();
-        let mut registers = stack.register_buf_cache.acquire(ir_block.register_count);
+
+        // Allocate and initialize registers. I've found that it's not really worth trying to avoid
+        // the heap allocation here by reusing buffers - our allocator is fast enough
+        let mut registers = Vec::with_capacity(ir_block.register_count);
+        let empty = std::iter::repeat_with(|| PipelineData::Empty);
+        registers.extend(empty.take(ir_block.register_count));
 
         let result = eval_ir_block_impl::<D>(
             &mut EvalContext {
@@ -44,7 +49,6 @@ pub fn eval_ir_block<D: DebugContext>(
             input,
         );
 
-        stack.register_buf_cache.release(registers);
         stack.error_handlers.leave_frame(error_handler_base);
         stack.arguments.leave_frame(args_base);
 
@@ -128,12 +132,6 @@ impl<'a> EvalContext<'a> {
 
         let mut new_stack = Box::new(self.stack.gather_captures(self.engine_state, &[]));
 
-        // Swap the RegisterBufCache onto the new stack so that we can reuse the buffers
-        std::mem::swap(
-            &mut self.stack.register_buf_cache,
-            &mut new_stack.register_buf_cache,
-        );
-
         // Increment recursion count on callee stack to prevent recursing too far
         new_stack.recursion_count += 1;
 
@@ -142,13 +140,8 @@ impl<'a> EvalContext<'a> {
 
     /// Drop the callee stack, so that arguments will be put on the caller stack instead
     fn drop_callee_stack(&mut self) {
-        if let Some(mut callee_stack) = self.callee_stack.take() {
-            // Swap the RegisterBufCache onto our stack so that we can reuse the buffers
-            std::mem::swap(
-                &mut callee_stack.register_buf_cache,
-                &mut self.stack.register_buf_cache,
-            );
-        }
+        // this is provided so in case some other cleanup needs to be done, it can be done here.
+        self.callee_stack = None;
     }
 }
 

crates/nu-protocol/src/engine/mod.rs

@@ -8,7 +8,6 @@ mod engine_state;
 mod error_handler;
 mod overlay;
 mod pattern_match;
-mod register_buf_cache;
 mod stack;
 mod stack_out_dest;
 mod state_delta;
@@ -27,7 +26,6 @@ pub use engine_state::*;
 pub use error_handler::*;
 pub use overlay::*;
 pub use pattern_match::*;
-pub use register_buf_cache::*;
 pub use stack::*;
 pub use stack_out_dest::*;
 pub use state_delta::*;

crates/nu-protocol/src/engine/register_buf_cache.rs

@@ -1,62 +0,0 @@
-use std::fmt;
-
-use crate::PipelineData;
-
-/// Retains buffers for reuse in IR evaluation, avoiding heap allocation.
-///
-/// This is implemented in such a way that [`Clone`] is still possible, by making the fact that the
-/// buffers can't be preserved on clone completely transparent. The cached buffers are always empty.
-pub struct RegisterBufCache {
-    bufs: Vec<Vec<PipelineData>>,
-}
-
-// SAFETY: because `bufs` only ever contains empty `Vec`s, it doesn't actually contain any of the
-// data.
-unsafe impl Send for RegisterBufCache {}
-unsafe impl Sync for RegisterBufCache {}
-
-impl RegisterBufCache {
-    /// Create a new cache with no register buffers.
-    pub const fn new() -> Self {
-        RegisterBufCache { bufs: vec![] }
-    }
-
-    /// Acquire a new register buffer from the cache. The buffer will be extended to `size` with
-    /// [`Empty`](PipelineData::Empty) elements.
-    pub fn acquire(&mut self, size: usize) -> Vec<PipelineData> {
-        let mut buf = if let Some(buf) = self.bufs.pop() {
-            debug_assert!(buf.is_empty());
-            buf
-        } else {
-            Vec::new()
-        };
-        buf.reserve(size);
-        buf.extend(std::iter::repeat_with(|| PipelineData::Empty).take(size));
-        buf
-    }
-
-    /// Release a used register buffer to the cache. The buffer will be cleared.
-    pub fn release(&mut self, mut buf: Vec<PipelineData>) {
-        // SAFETY: this `clear` is necessary for the `unsafe impl`s to be safe
-        buf.clear();
-        self.bufs.push(buf);
-    }
-}
-
-impl fmt::Debug for RegisterBufCache {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let bufs = self.bufs.len();
-        let bytes: usize = self
-            .bufs
-            .iter()
-            .map(|b| b.capacity() * std::mem::size_of::<PipelineData>())
-            .sum();
-        write!(f, "RegisterBufCache({bufs} bufs, {bytes} bytes)")
-    }
-}
-
-impl Clone for RegisterBufCache {
-    fn clone(&self) -> Self {
-        RegisterBufCache::new()
-    }
-}

crates/nu-protocol/src/engine/stack.rs

@@ -1,7 +1,7 @@
 use crate::{
     engine::{
-        ArgumentStack, EngineState, ErrorHandlerStack, Redirection, RegisterBufCache,
-        StackCallArgGuard, StackCaptureGuard, StackIoGuard, StackOutDest, DEFAULT_OVERLAY_NAME,
+        ArgumentStack, EngineState, ErrorHandlerStack, Redirection, StackCallArgGuard,
+        StackCaptureGuard, StackIoGuard, StackOutDest, DEFAULT_OVERLAY_NAME,
     },
     OutDest, ShellError, Span, Value, VarId, ENV_VARIABLE_ID, NU_VARIABLE_ID,
 };
@@ -41,8 +41,6 @@ pub struct Stack {
     pub env_hidden: HashMap<String, HashSet<String>>,
     /// List of active overlays
     pub active_overlays: Vec<String>,
-    /// Cached register buffers for IR evaluation
-    pub register_buf_cache: RegisterBufCache,
     /// Argument stack for IR evaluation
     pub arguments: ArgumentStack,
     /// Error handler stack for IR evaluation
@@ -76,7 +74,6 @@ impl Stack {
             env_vars: Vec::new(),
             env_hidden: HashMap::new(),
             active_overlays: vec![DEFAULT_OVERLAY_NAME.to_string()],
-            register_buf_cache: RegisterBufCache::new(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
             use_ir: false,
@@ -97,7 +94,6 @@ impl Stack {
             env_vars: parent.env_vars.clone(),
             env_hidden: parent.env_hidden.clone(),
             active_overlays: parent.active_overlays.clone(),
-            register_buf_cache: RegisterBufCache::new(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
             use_ir: parent.use_ir,
@@ -270,7 +266,6 @@ impl Stack {
             env_vars,
             env_hidden: self.env_hidden.clone(),
             active_overlays: self.active_overlays.clone(),
-            register_buf_cache: RegisterBufCache::new(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
             use_ir: self.use_ir,
@@ -304,7 +299,6 @@ impl Stack {
             env_vars,
             env_hidden: self.env_hidden.clone(),
             active_overlays: self.active_overlays.clone(),
-            register_buf_cache: RegisterBufCache::new(),
             arguments: ArgumentStack::new(),
             error_handlers: ErrorHandlerStack::new(),
             use_ir: self.use_ir,