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LibJS: Add basic support for while loops in the bytecode engine

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This introduces two new instructions: Jump and JumpIfFalse.
Jumps are made to a Bytecode::Label, which is a simple object that
represents a location in the bytecode stream.

Note that you may not always know the target of a jump when adding the
jump instruction itself, but we can just update the instruction later
on during codegen once we know where the jump target is.

The Bytecode::Interpreter now implements jumping via a jump slot that
gets checked after each instruction to see if a jump is pending.
If not, we just increment the PC as usual.
This commit is contained in:
Andreas Kling 2021-06-04 12:07:38 +02:00
parent 91640d0727
commit 6ae9346cd3
9 changed files with 128 additions and 1 deletions
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25
Userland/Libraries/LibJS/Bytecode/Op.cpp
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@ -46,6 +46,19 @@ void SetVariable::execute(Bytecode::Interpreter& interpreter) const
interpreter.vm().set_variable(m_identifier, interpreter.reg(m_src), interpreter.global_object());
}
void Jump::execute(Bytecode::Interpreter& interpreter) const
{
interpreter.jump(m_target);
}
void JumpIfFalse::execute(Bytecode::Interpreter& interpreter) const
{
VERIFY(m_target.has_value());
auto result = interpreter.reg(m_result);
if (!result.as_bool())
interpreter.jump(m_target.value());
}
String Load::to_string() const
{
return String::formatted("Load dst:{}, value:{}", m_dst, m_value.to_string_without_side_effects());
@ -81,4 +94,16 @@ String SetVariable::to_string() const
return String::formatted("SetVariable identifier:{}, src:{}", m_identifier, m_src);
}
String Jump::to_string() const
{
return String::formatted("Jump {}", m_target);
}
String JumpIfFalse::to_string() const
{
if (m_target.has_value())
return String::formatted("JumpIfFalse result:{}, target:{}", m_result, m_target.value());
return String::formatted("JumpIfFalse result:{}, target:<empty>", m_result);
}
}