Hi all.
I'm trying to understand how resolve_global instruction works for several
days. Let's look at the code
void JIT::emit_op_resolve_global(Instruction* currentInstruction, bool)
{
// Fast case
void* globalObject = m_codeBlock->globalObject();
unsigned currentIndex = m_globalResolveInfoIndex++;
GlobalResolveInfo* resolveInfoAddress =
&(m_codeBlock->globalResolveInfo(currentIndex));
// Check Structure of global object
move(TrustedImmPtr(globalObject), regT0); //*loads address of
globalObject to eax(regT0)*
move(TrustedImmPtr(resolveInfoAddress), regT2);*// loads address
of resolveInfoAddress to ecx(regT2)*
loadPtr(Address(regT2, OBJECT_OFFSETOF(GlobalResolveInfo, structure)),
regT1);
addSlowCase(branchPtr(NotEqual, regT1, Address(regT0,
JSCell::structureOffset()))); // Structures don't match *// Do some checking
*
// Load cached property
// Assume that the global object always uses external storage.
loadPtr(Address(regT0, OBJECT_OFFSETOF(JSGlobalObject,
m_propertyStorage)), regT0); *// loads m_propertyStorage to eax*
*
*
*// Here is interesting thing happens*
*// offset member of GlobalResolveInfo class is always 0;*
load32(Address(regT2, OBJECT_OFFSETOF(GlobalResolveInfo, offset)),
regT1); *//move value of **GlobalResolveInfo offset member(it's always 0 )
to edx(regT1)*
*//So here we always mov same value to eax(regT0), regardless of whether
our global Array , String or Object*
loadPtr(BaseIndex(regT0, regT1, ScalePtr), regT0);
emitValueProfilingSite();
emitPutVirtualRegister(currentInstruction[1].u.operand);
}
So
1. What is mystery of this instruction, how it's really works let's say for
this example???
var a=Array(5);
var s=String;
var o=Object;
2. What is in m_propertyStorage, and when it's sets?
Thanks for attention!