+/// ResolveConstantForwardRefs - Once all constants are read, this method bulk
+/// resolves any forward references. The idea behind this is that we sometimes
+/// get constants (such as large arrays) which reference *many* forward ref
+/// constants. Replacing each of these causes a lot of thrashing when
+/// building/reuniquing the constant. Instead of doing this, we look at all the
+/// uses and rewrite all the place holders at once for any constant that uses
+/// a placeholder.
+void BitcodeReaderValueList::ResolveConstantForwardRefs() {
+ // Sort the values by-pointer so that they are efficient to look up with a
+ // binary search.
+ std::sort(ResolveConstants.begin(), ResolveConstants.end());
+
+ SmallVector<Constant*, 64> NewOps;
+
+ while (!ResolveConstants.empty()) {
+ Value *RealVal = operator[](ResolveConstants.back().second);
+ Constant *Placeholder = ResolveConstants.back().first;
+ ResolveConstants.pop_back();
+
+ // Loop over all users of the placeholder, updating them to reference the
+ // new value. If they reference more than one placeholder, update them all
+ // at once.
+ while (!Placeholder->use_empty()) {
+ Value::use_iterator UI = Placeholder->use_begin();
+
+ // If the using object isn't uniqued, just update the operands. This
+ // handles instructions and initializers for global variables.
+ if (!isa<Constant>(*UI) || isa<GlobalValue>(*UI)) {
+ UI.getUse().set(RealVal);
+ continue;
+ }
+
+ // Otherwise, we have a constant that uses the placeholder. Replace that
+ // constant with a new constant that has *all* placeholder uses updated.
+ Constant *UserC = cast<Constant>(*UI);
+ for (User::op_iterator I = UserC->op_begin(), E = UserC->op_end();
+ I != E; ++I) {
+ Value *NewOp;
+ if (!isa<ConstantPlaceHolder>(*I)) {
+ // Not a placeholder reference.
+ NewOp = *I;
+ } else if (*I == Placeholder) {
+ // Common case is that it just references this one placeholder.
+ NewOp = RealVal;
+ } else {
+ // Otherwise, look up the placeholder in ResolveConstants.
+ ResolveConstantsTy::iterator It =
+ std::lower_bound(ResolveConstants.begin(), ResolveConstants.end(),
+ std::pair<Constant*, unsigned>(cast<Constant>(*I),
+ 0));
+ assert(It != ResolveConstants.end() && It->first == *I);
+ NewOp = operator[](It->second);
+ }
+
+ NewOps.push_back(cast<Constant>(NewOp));
+ }
+
+ // Make the new constant.
+ Constant *NewC;
+ if (ConstantArray *UserCA = dyn_cast<ConstantArray>(UserC)) {
+ NewC = Context.getConstantArray(UserCA->getType(), &NewOps[0],
+ NewOps.size());
+ } else if (ConstantStruct *UserCS = dyn_cast<ConstantStruct>(UserC)) {
+ NewC = Context.getConstantStruct(&NewOps[0], NewOps.size(),
+ UserCS->getType()->isPacked());
+ } else if (isa<ConstantVector>(UserC)) {
+ NewC = Context.getConstantVector(&NewOps[0], NewOps.size());
+ } else {
+ assert(isa<ConstantExpr>(UserC) && "Must be a ConstantExpr.");
+ NewC = cast<ConstantExpr>(UserC)->getWithOperands(&NewOps[0],
+ NewOps.size());
+ }
+
+ UserC->replaceAllUsesWith(NewC);
+ UserC->destroyConstant();
+ NewOps.clear();
+ }
+
+ // Update all ValueHandles, they should be the only users at this point.
+ Placeholder->replaceAllUsesWith(RealVal);
+ delete Placeholder;
+ }
+}
+