[FnSpecialization] Allow chains to form when collapsing PHI nodes

Author: bababuck

llvm/include/llvm/Transforms/IPO/FunctionSpecialization.h

@@ -228,7 +228,8 @@ class InstCostVisitor : public InstVisitor<InstCostVisitor, Constant *> {
   LLVM_ABI Cost getCodeSizeSavingsForArg(Argument *A, Constant *C,
                                          CallUserT *CallUsers = nullptr);
 
-  LLVM_ABI Cost getCodeSizeSavingsFromPendingPHIs();
+  LLVM_ABI Cost
+  getCodeSizeSavingsFromPendingPHIs(CallUserT *CallUsers = nullptr);
 
   LLVM_ABI Cost getLatencySavingsForKnownConstants();
 

llvm/lib/Transforms/IPO/FunctionSpecialization.cpp

@@ -154,13 +154,14 @@ Constant *InstCostVisitor::findConstantFor(Value *V) const {
   return KnownConstants.lookup(V);
 }
 
-Cost InstCostVisitor::getCodeSizeSavingsFromPendingPHIs() {
+Cost InstCostVisitor::getCodeSizeSavingsFromPendingPHIs(CallUserT *CallUsers) {
   Cost CodeSize;
   while (!PendingPHIs.empty()) {
     Instruction *Phi = PendingPHIs.pop_back_val();
     // The pending PHIs could have been proven dead by now.
     if (isBlockExecutable(Phi->getParent()))
-      CodeSize += getCodeSizeSavingsForUser(Phi);
+      CodeSize +=
+          getCodeSizeSavingsForUser(Phi, nullptr, nullptr, CallUsers, nullptr);
   }
   return CodeSize;
 }
@@ -1116,7 +1117,7 @@ bool FunctionSpecializer::findSpecializations(
         Score += getInliningBonus(A.Formal, A.Actual);
       }
 
-      CodeSize += Visitor.getCodeSizeSavingsFromPendingPHIs();
+      CodeSize += Visitor.getCodeSizeSavingsFromPendingPHIs(&CallUsers);
       CurrentChain.insert(F);
 
       for (auto &CU : CallUsers) {