这里定义的意思就是，istore使用无参数的生成器istore函数生成例程，这个生成器正是之前提到的那个很短的汇编代码：
void TemplateTable::istore() {
transition(itos, vtos);
locals_index(rbx);
__ movl(iaddress(rbx), rax);
}
ubcp表示使用字节码指针，所谓字节码指针指的是该字节码的操作数是否存在于字节码里面,一图胜千言：
istore的index紧跟在istore(0x36)后面，所以istore需要移动字节码指针以获取index。
istore还规定执行前栈顶缓存int值(itos)，执行后不缓存(vtos)，且istore还有一个wide版本，这个版本使用两个字节的index。
有了这些信息，可以试着解释多出的汇编是怎么回事了。set_entry_points()为istore和wide版本的istore生成代码，
我们选择普通版本的istore解释，wide版本的依样画葫芦即可。它又进一步调用了set_short_entry_points()：
void TemplateInterpreterGenerator::set_entry_points(Bytecodes::Code code) {
...
if (Bytecodes::is_defined(code)) {
Template* t = TemplateTable::template_for(code);
assert(t->is_valid(), "just checking");
set_short_entry_points(t, bep, cep, sep, aep, iep, lep, fep, dep, vep);
}
if (Bytecodes::wide_is_defined(code)) {
Template* t = TemplateTable::template_for_wide(code);
assert(t->is_valid(), "just checking");
set_wide_entry_point(t, wep);
}
...
}
void TemplateInterpreterGenerator::set_short_entry_points(Template* t, address& bep, address& cep, address& sep, address& aep, address& iep, address& lep, address& fep, address& dep, address& vep) {
assert(t->is_valid(), "template must exist");
switch (t->tos_in()) {
case btos:
case ztos:
case ctos:
case stos:
ShouldNotReachHere(); // btos/ctos/stos should use itos.
break;
case atos: vep = __ pc(); __ pop(atos); aep = __ pc(); generate_and_dispatch(t); break;
case itos: vep = __ pc(); __ pop(itos); iep = __ pc(); generate_and_dispatch(t); break;
case ltos: vep = __ pc(); __ pop(ltos); lep = __ pc(); generate_and_dispatch(t); break;
case ftos: vep = __ pc(); __ pop(ftos); fep = __ pc(); generate_and_dispatch(t); break;
case dtos: vep = __ pc(); __ pop(dtos); dep = __ pc(); generate_and_dispatch(t); break;
case vtos: set_vtos_entry_points(t, bep, cep, sep, aep, iep, lep, fep, dep, vep);
break;
default : ShouldNotReachHere();
break;
}
}
set_short_entry_points会根据该指令执行前是否需要栈顶缓存pop数据，istore使用了itos缓存，所以需要pop：
// hotspot\src\cpu\x86\vm\interp_masm_x86.cpps
void InterpreterMacroAssembler::pop_i(Register r) {
// XXX can't use pop currently, upper half non clean
movl(r, Address(rsp, 0));
addptr(rsp, wordSize);
}
稍微需要注意的是这里说的pop是一个弹出的概念，实际生成的代码是mov，试着解释那一大堆汇编：
mov指令
----------------------------------------------------------------------
istore 54 istore [0x00000192d1972ba0, 0x00000192d1972c00] 96 bytes
;获取栈顶int缓存
0x00000192d1972ba0: mov (%rsp),%eax
0x00000192d1972ba3: add $0x8,%rsp
0x00000192d1972ba7: movzbl 0x1(%r13),%ebx
0x00000192d1972bac: neg %rbx
0x00000192d1972baf: mov %eax,(%r14,%rbx,8)
0x00000192d1972bb3: movzbl 0x2(%r13),%ebx
0x00000192d1972bb8: add $0x2,%r13
0x00000192d1972bbc: movabs $0x7fffd56e0fa0,%r10
0x00000192d1972bc6: jmpq *(%r10,%rbx,8)
0x00000192d1972bca: mov (%rsp),%eax
0x00000192d1972bcd: add $0x8,%rsp
0x00000192d1972bd1: movzwl 0x2(%r13),%ebx
0x00000192d1972bd6: bswap %ebx
0x00000192d1972bd8: shr $0x10,%ebx
0x00000192d1972bdb: neg %rbx
0x00000192d1972bde: mov %eax,(%r14,%rbx,8)
0x00000192d1972be2: movzbl 0x4(%r13),%ebx
0x00000192d1972be7: add $0x4,%r13
0x00000192d1972beb: movabs $0x7fffd56e0fa0,%r10
0x00000192d1972bf5: jmpq *(%r10,%rbx,8)
0x00000192d1972bf9: nopl 0x0(%rax)
接着generate_and_dispatch()又分为执行前(dispatch_prolog)+执行字节码(t->generate())+执行后三部分(dispatch_epilog):
void TemplateInterpreterGenerator::generate_and_dispatch(Template* t, TosState tos_out) {
...
int step = 0;
if (!t->does_dispatch()) {
step = t->is_wide() ? Bytecodes::wide_length_for(t->bytecode()) : Bytecodes::length_for(t->bytecode());
if (tos_out == ilgl) tos_out = t->tos_out();
// compute bytecode size
assert(step > 0, "just checkin'");
// setup stuff for dispatching next bytecode
if (ProfileInterpreter && VerifyDataPointer
&& MethodData::bytecode_has_profile(t->bytecode())) {
__ verify_method_data_pointer();
}
__ dispatch_prolog(tos_out, step);
}
// generate template
t->generate(_masm);
// advance
if (t->does_dispatch()) {
#ifdef ASSERT
// make sure execution doesn't go beyond this point if code is broken
__ should_not_reach_here();
#endif // ASSERT
} else {
// dispatch to next bytecode
__ dispatch_epilog(tos_out, step);
}
}
