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LibJS/JIT: Add fast path for decrement

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Generate jitted code for the decrement opcode.
This commit is contained in:
Stephan Vedder 2023-11-07 16:56:14 +01:00 committed by Andreas Kling
parent 0e69f744df
commit 13726fd3b7
Notes: sideshowbarker 2024-07-17 07:16:27 +09:00 
Author: https://github.com/feliwir
Commit: https://github.com/SerenityOS/serenity/commit/13726fd3b7
Pull-request: https://github.com/SerenityOS/serenity/pull/21841
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/skyrising
2 changed files with 47 additions and 0 deletions
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15
Userland/Libraries/LibJIT/X86_64/Assembler.h
View file

@ -757,6 +757,21 @@ struct X86_64Assembler {
}
}
void dec32(Operand op, Optional<Label&> overflow_label)
{
if (op.is_register_or_memory()) {
emit_rex_for_slash(op, REX_W::No);
emit8(0xff);
emit_modrm_slash(1, op);
} else {
VERIFY_NOT_REACHED();
}
if (overflow_label.has_value()) {
jump_if(Condition::Overflow, *overflow_label);
}
}
void add(Operand dst, Operand src)
{
if (dst.is_register_or_memory() && src.type == Operand::Type::Reg) {

32
Userland/Libraries/LibJS/JIT/Compiler.cpp
View file

@ -396,9 +396,41 @@ static Value cxx_decrement(VM& vm, Value value)
void Compiler::compile_decrement(Bytecode::Op::Decrement const&)
{
load_accumulator(ARG1);
Assembler::Label end {};
Assembler::Label slow_case {};
branch_if_int32(ARG1, [&] {
// GPR0 = ARG1;
m_assembler.mov(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Register(ARG1));
// GPR0--;
m_assembler.dec32(
Assembler::Operand::Register(GPR0),
slow_case);
// accumulator = GPR0 | SHIFTED_INT32_TAG;
m_assembler.mov(
Assembler::Operand::Register(GPR1),
Assembler::Operand::Imm(SHIFTED_INT32_TAG));
m_assembler.bitwise_or(
Assembler::Operand::Register(GPR0),
Assembler::Operand::Register(GPR1));
// accumulator = GPR0;
store_accumulator(GPR0);
m_assembler.jump(end);
});
slow_case.link(m_assembler);
native_call((void*)cxx_decrement);
store_accumulator(RET);
check_exception();
end.link(m_assembler);
}
void Compiler::check_exception()