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LibWasm: Try really hard to avoid touching the value stack

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This commit adds a register allocator, with 8 available "register"
slots.
In testing with various random blobs, this moves anywhere from 30% to
74% of value accesses into predefined slots, and is about a ~20% perf
increase end-to-end.

To actually make this usable, a few structural changes were also made:
- we no longer do one instruction per interpret call
- trapping is an (unlikely) exit condition
- the label and frame stacks are replaced with linked lists with a huge
  node cache size, as we only need to touch the last element and
  push/pop is very frequent.
This commit is contained in:
Ali Mohammad Pur 2025-08-02 20:30:44 +02:00 • committed by Ali Mohammad Pur
commit 0e5ecef848
Notes: github-actions[bot] 2025-08-08 10:55:57 +00:00
9 changed files with 3217 additions and 1824 deletions
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11
Libraries/LibWasm/AbstractMachine/Validator.cpp
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@ -1337,7 +1337,7 @@ VALIDATE_INSTRUCTION(select_typed)
// https://webassembly.github.io/spec/core/bikeshed/#variable-instructions%E2%91%A2
VALIDATE_INSTRUCTION(local_get)
{
auto index = instruction.arguments().get<LocalIndex>();
auto index = instruction.local_index();
TRY(validate(index));
stack.append(m_context.locals[index.value()]);
@ -1346,7 +1346,7 @@ VALIDATE_INSTRUCTION(local_get)
VALIDATE_INSTRUCTION(local_set)
{
auto index = instruction.arguments().get<LocalIndex>();
auto index = instruction.local_index();
TRY(validate(index));
auto& value_type = m_context.locals[index.value()];
@ -1357,7 +1357,7 @@ VALIDATE_INSTRUCTION(local_set)
VALIDATE_INSTRUCTION(local_tee)
{
auto index = instruction.arguments().get<LocalIndex>();
auto index = instruction.local_index();
TRY(validate(index));
auto& value_type = m_context.locals[index.value()];
@ -3699,7 +3699,7 @@ VALIDATE_INSTRUCTION(f64x2_convert_low_i32x4_u)
ErrorOr<void, ValidationError> Validator::validate(Instruction const& instruction, Stack& stack, bool& is_constant)
{
switch (instruction.opcode().value()) {
#define M(name, integer_value) \
#define M(name, integer_value, ...) \
case Instructions::name.value(): \
dbgln_if(WASM_VALIDATOR_DEBUG, "checking {}, stack = {}", #name, stack); \
return validate_instruction<integer_value>(instruction, stack, is_constant);
@ -3738,6 +3738,9 @@ ErrorOr<Validator::ExpressionTypeResult, ValidationError> Validator::validate(Ex
expression.set_stack_usage_hint(stack.max_known_size());
// Now that we're in happy land, try to compile the expression down to a list of labels to help dispatch.
expression.compiled_instructions = try_compile_instructions(expression, m_context.functions.span());
return ExpressionTypeResult { stack.release_vector(), is_constant_expression };
}