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LibJS/JIT: Only preserve VM& when making native call to C++
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! :^)
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1 changed files with 12 additions and 19 deletions
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@ -1006,28 +1006,21 @@ void Compiler::jump_to_exit()
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void Compiler::native_call(void* function_address, Vector<Assembler::Operand> const& stack_arguments)
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{
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// push caller-saved registers on the stack
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// (callee-saved registers: RBX, RSP, RBP, and R12–R15)
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RCX));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RDX));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RSI));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::RDI));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R8));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R9));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R10));
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m_assembler.push(Assembler::Operand::Register(Assembler::Reg::R11));
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// Make sure we don't clobber the VM&.
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m_assembler.push(Assembler::Operand::Register(ARG0));
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// Align the stack pointer.
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m_assembler.sub(Assembler::Operand::Register(STACK_POINTER), Assembler::Operand::Imm(8));
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// NOTE: We don't preserve caller-saved registers when making a native call.
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// This means that they may have changed after we return from the call.
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m_assembler.native_call(function_address, stack_arguments);
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// restore caller-saved registers from the stack
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R11));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R10));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R9));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::R8));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RDI));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RSI));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RDX));
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m_assembler.pop(Assembler::Operand::Register(Assembler::Reg::RCX));
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// Restore the stack pointer.
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m_assembler.add(Assembler::Operand::Register(STACK_POINTER), Assembler::Operand::Imm(8));
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// Restore our VM&.
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m_assembler.pop(Assembler::Operand::Register(ARG0));
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}
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OwnPtr<NativeExecutable> Compiler::compile(Bytecode::Executable& bytecode_executable)
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