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⚡ Bolt: [performance improvement] Remove redundant function lookup in VM loop #27

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Merged
Tcode-Motion merged 1 commit into from
Aug 25, 2026
Merged

⚡ Bolt: [performance improvement] Remove redundant function lookup in VM loop #27

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1 change: 1 addition & 0 deletions .jules/bolt.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
## 2026-08-19 - Removed redundant instruction array lookup in VM loop
**Learning:** The inner loop of the VM interpreter (`execute_loop`) had an expensive, redundant deep indexing operation to fetch `inst_operands` which was already available on the `inst` reference. Re-fetching it via `self.module.functions[...].chunk.instructions[...].operands` adds unnecessary bounds checks and pointer chasing in the hottest part of the VM.
**Action:** Always prefer using existing local references over redundant deep lookups, especially in tight loops like an interpreter fetch-decode-execute loop.
## 2026-08-19 - Reused local frame and func references in VM opcodes\n**Learning:** The VM executor repeatedly looked up the current frame via `self.frames.last()` and current function via `self.module.functions[...]` in several opcodes (LoadConst, FieldLoad, StoreLocal, etc.). This adds unnecessary bounds checking and pointer dereferencing on the hottest path since `frame` and `func` are already computed at the start of the while loop iteration.\n**Action:** Always reuse existing local references in tight loop opcodes rather than repeatedly querying collections or stacks when the target element is already known and borrowed.
44 changes: 6 additions & 38 deletions runtime/vm/src/executor.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,14 +35,8 @@ impl VM {
self.profiler.record_stack_height(self.stack.len());

if self.debugger.is_enabled() {
let current_func = &self.module.functions[self
.frames
.last()
.ok_or(crate::error::VMError::StackUnderflow)?
.function_idx
as usize];
self.debugger.trace_instruction(
current_func,
func,
ip,
inst_op,
inst_operands,
Expand All @@ -55,13 +49,7 @@ impl VM {

Opcode::LoadConst => {
if let Some(Operand::ConstantIndex(c_idx)) = inst_operands.first() {
let current_func = &self.module.functions[self
.frames
.last()
.ok_or(crate::error::VMError::StackUnderflow)?
.function_idx
as usize];
let lit = current_func
let lit = func
.chunk
.constants
.get(*c_idx)
Expand All @@ -81,11 +69,7 @@ impl VM {

Opcode::LoadLocal => {
if let Some(Operand::LocalIndex(l_idx)) = inst_operands.first() {
let bp = self
.frames
.last()
.ok_or(crate::error::VMError::StackUnderflow)?
.base_pointer;
let bp = frame.base_pointer;
let val = self.stack.get(bp + *l_idx as usize)?;
self.stack.push(val.clone())?;
} else {
Expand All @@ -95,11 +79,7 @@ impl VM {

Opcode::StoreLocal => {
if let Some(Operand::LocalIndex(l_idx)) = inst_operands.first() {
let bp = self
.frames
.last()
.ok_or(crate::error::VMError::StackUnderflow)?
.base_pointer;
let bp = frame.base_pointer;
let val = self.stack.pop()?;
self.stack.set(bp + *l_idx as usize, val)?;
} else {
Expand Down Expand Up @@ -784,13 +764,7 @@ impl VM {

Opcode::FieldLoad => {
if let Some(Operand::ConstantIndex(c_idx)) = inst_operands.first() {
let current_func = &self.module.functions[self
.frames
.last()
.ok_or(crate::error::VMError::StackUnderflow)?
.function_idx
as usize];
let lit = current_func
let lit = func
.chunk
.constants
.get(*c_idx)
Expand Down Expand Up @@ -846,13 +820,7 @@ impl VM {

Opcode::FieldStore => {
if let Some(Operand::ConstantIndex(c_idx)) = inst_operands.first() {
let current_func = &self.module.functions[self
.frames
.last()
.ok_or(crate::error::VMError::StackUnderflow)?
.function_idx
as usize];
let lit = current_func
let lit = func
.chunk
.constants
.get(*c_idx)
Expand Down
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