/**
* Determines whether this block is guaranteed to begin executing before the given block does.
*/
boolean provablyExecutesBefore(BasicBlock thatBlock) {
// If thatBlock is a descendant of this block, and there are no hoisted
// blocks between them, then this block must start before thatBlock.
BasicBlock currentBlock;
for (currentBlock = thatBlock;
currentBlock != null && currentBlock != this;
currentBlock = currentBlock.getParent()) {}
if (currentBlock == this) {
return true;
}
return isGlobalScopeBlock() && thatBlock.isGlobalScopeBlock();
}
/** @return Whether the variable is only assigned a value once for its lifetime. */
boolean isAssignedOnceInLifetime() {
Reference ref = getOneAndOnlyAssignment();
if (ref == null) {
return false;
}
// Make sure this assignment is not in a loop.
for (BasicBlock block = ref.getBasicBlock(); block != null; block = block.getParent()) {
if (block.isFunction) {
if (ref.getSymbol().getScope() != ref.scope) {
return false;
}
break;
} else if (block.isLoop) {
return false;
}
}
return true;
}
/**
* Determines if the variable for this reference collection is "well-defined." A variable is
* well-defined if we can prove at compile-time that it's assigned a value before it's used.
*
* <p>Notice that if this function returns false, this doesn't imply that the variable is used
* before it's assigned. It just means that we don't have enough information to make a
* definitive judgment.
*/
protected boolean isWellDefined() {
int size = references.size();
if (size == 0) {
return false;
}
// If this is a declaration that does not instantiate the variable,
// it's not well-defined.
Reference init = getInitializingReference();
if (init == null) {
return false;
}
Preconditions.checkState(references.get(0).isDeclaration());
BasicBlock initBlock = init.getBasicBlock();
for (int i = 1; i < size; i++) {
if (!initBlock.provablyExecutesBefore(references.get(i).getBasicBlock())) {
return false;
}
}
return true;
}