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LibJS/JIT: Only preserve VM& when making native call to C++

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Instead of pushing and popping every single caller-saved registers,
we can optimize code size (and speed!) by only pushing the one register
we actually care about: RDI (since it holds our VM&).

This means that native calls may clobber every other caller-saved
register, so this is something that you have to be aware of when
emitting native calls in the JIT.

This reduces code size on Kraken/ai-astar.js by 553 KiB and makes
execution time ~6% faster as well! :^)
This commit is contained in:
Andreas Kling 2023-10-28 14:22:36 +02:00
parent 926786e8d1
commit fff82c5ffe
1 changed files with 12 additions and 19 deletions
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31
Userland/Libraries/LibJS/JIT/Compiler.cpp
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@ -1006,28 +1006,21 @@ void Compiler::jump_to_exit()
void Compiler::native_call(void* function_address, Vector<Assembler::Operand> const& stack_arguments)
{
// push caller-saved registers on the stack
// (callee-saved registers: RBX, RSP, RBP, and R12–R15)
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RCX));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RDX));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RSI));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RDI));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R8));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R9));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R10));
m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R11));
// Make sure we don't clobber the VM&.
m_assembler.push(Assembler::Operand::Register(ARG0));
// Align the stack pointer.
m_assembler.sub(Assembler::Operand::Register(STACK_POINTER), Assembler::Operand::Imm(8));
// NOTE: We don't preserve caller-saved registers when making a native call.
// This means that they may have changed after we return from the call.
m_assembler.native_call(function_address, stack_arguments);
// restore caller-saved registers from the stack
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R11));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R10));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R9));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R8));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RDI));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RSI));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RDX));
m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RCX));
// Restore the stack pointer.
m_assembler.add(Assembler::Operand::Register(STACK_POINTER), Assembler::Operand::Imm(8));
// Restore our VM&.
m_assembler.pop(Assembler::Operand::Register(ARG0));
}
OwnPtr<NativeExecutable> Compiler::compile(Bytecode::Executable& bytecode_executable)