[llvm] [FuncSpec] Only compute Latency bonus when necessary (PR #113159)

[Alexandros Lamprineas via llvm-commits]

================
@@ -154,37 +154,55 @@ static Constant *findConstantFor(Value *V, ConstMap &KnownConstants) {
   return KnownConstants.lookup(V);
 }
 
-Bonus InstCostVisitor::getBonusFromPendingPHIs() {
-  Bonus B;
+Cost InstCostVisitor::getCodeSizeBonusFromPendingPHIs() {
+  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()))
-      B += getUserBonus(Phi);
+      CodeSize += getUserCodeSizeBonus(Phi);
   }
-  return B;
+  return CodeSize;
 }
 
-/// Compute a bonus for replacing argument \p A with constant \p C.
-Bonus InstCostVisitor::getSpecializationBonus(Argument *A, Constant *C) {
+/// Compute the codesize savings for replacing argument \p A with constant \p C.
+Cost InstCostVisitor::getCodeSizeBonus(Argument *A, Constant *C) {
   LLVM_DEBUG(dbgs() << "FnSpecialization: Analysing bonus for constant: "
                     << C->getNameOrAsOperand() << "\n");
-  Bonus B;
+  Cost CodeSize;
   for (auto *U : A->users())
     if (auto *UI = dyn_cast<Instruction>(U))
       if (isBlockExecutable(UI->getParent()))
-        B += getUserBonus(UI, A, C);
+        CodeSize += getUserCodeSizeBonus(UI, A, C);
 
   LLVM_DEBUG(dbgs() << "FnSpecialization:   Accumulated bonus {CodeSize = "
-                    << B.CodeSize << ", Latency = " << B.Latency
-                    << "} for argument " << *A << "\n");
-  return B;
+                    << CodeSize << "} for argument " << *A << "\n");
+  return CodeSize;
+}
+
+Cost InstCostVisitor::getLatencyBonus() {
----------------
labrinea wrote:

We must be very careful here. The KnownConstants span for the lifetime of InstCostVisitor. If we separate the CodeSize savings calculation from that of LatencySavings, we must ensure they are in sync (calculated upon the same instructions we have visited and replaced by a constant). This also deserves a comment.

https://github.com/llvm/llvm-project/pull/113159