void
ValueNumberer::breakClass(MDefinition *def)
{
if (def->valueNumber() == def->id()) {
IonSpew(IonSpew_GVN, "Breaking congruence with itself: %d", def->id());
ValueNumberData *defdata = def->valueNumberData();
JS_ASSERT(defdata->classPrev == NULL);
// If the def was the only member of the class, then there is nothing to do.
if (defdata->classNext == NULL)
return;
// If upon closer inspection, we are still equivalent to this class
// then there isn't anything for us to do.
MDefinition *newRep = findSplit(def);
if (!newRep)
return;
ValueNumberData *newdata = newRep->valueNumberData();
// Right now, |defdata| is at the front of the list, and |newdata| is
// somewhere in the middle.
//
// We want to move |defdata| and everything up to but excluding
// |newdata| to a new list, with |defdata| still as the canonical
// element.
//
// We then want to take |newdata| and everything after, and
// mark them for processing (since |newdata| is now a new canonical
// element).
//
MDefinition *lastOld = newdata->classPrev;
JS_ASSERT(lastOld); // newRep is NOT the first element of the list.
JS_ASSERT(lastOld->valueNumberData()->classNext == newRep);
//lastOld is now the last element of the old list (congruent to
//|def|)
lastOld->valueNumberData()->classNext = NULL;
#ifdef DEBUG
for (MDefinition *tmp = def; tmp != NULL; tmp = tmp->valueNumberData()->classNext) {
JS_ASSERT(tmp->valueNumber() == def->valueNumber());
JS_ASSERT(tmp->congruentTo(def));
JS_ASSERT(tmp != newRep);
}
#endif
//|newRep| is now the first element of a new list, therefore it is the
//new canonical element. Mark the remaining elements in the list
//(including |newRep|)
newdata->classPrev = NULL;
IonSpew(IonSpew_GVN, "Choosing a new representative: %d", newRep->id());
// make the VN of every member in the class the VN of the new representative number.
for (MDefinition *tmp = newRep; tmp != NULL; tmp = tmp->valueNumberData()->classNext) {
// if this instruction is already scheduled to be processed, don't do anything.
if (tmp->isInWorklist())
continue;
IonSpew(IonSpew_GVN, "Moving to a new congruence class: %d", tmp->id());
tmp->setValueNumber(newRep->id());
markConsumers(tmp);
markDefinition(tmp);
}
// Insert the new representative => number mapping into the table
// Logically, there should not be anything in the table currently, but
// old values are never removed, so there's a good chance something will
// already be there.
values.put(newRep, newRep->id());
} else {
// The element that is breaking from the list isn't the representative element
// just strip it from the list
ValueNumberData *defdata = def->valueNumberData();
if (defdata->classPrev)
defdata->classPrev->valueNumberData()->classNext = defdata->classNext;
if (defdata->classNext)
defdata->classNext->valueNumberData()->classPrev = defdata->classPrev;
// Make sure there is no nastinees accidentally linking elements into the old list later.
defdata->classPrev = NULL;
defdata->classNext = NULL;
}
}
