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

[Hari Limaye via llvm-commits]

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@@ -875,48 +909,67 @@ bool FunctionSpecializer::findSpecializations(Function *F, unsigned FuncSize,
       AllSpecs[Index].CallSites.push_back(&CS);
     } else {
       // Calculate the specialisation gain.
-      Bonus B;
+      Cost CodeSize;
       unsigned Score = 0;
       InstCostVisitor Visitor = getInstCostVisitorFor(F);
       for (ArgInfo &A : S.Args) {
-        B += Visitor.getSpecializationBonus(A.Formal, A.Actual);
+        CodeSize += Visitor.getCodeSizeSavingsForArg(A.Formal, A.Actual);
         Score += getInliningBonus(A.Formal, A.Actual);
       }
-      B += Visitor.getBonusFromPendingPHIs();
-
+      CodeSize += Visitor.getCodeSizeSavingsFromPendingPHIs();
 
-      LLVM_DEBUG(dbgs() << "FnSpecialization: Specialization bonus {CodeSize = "
-                        << B.CodeSize << ", Latency = " << B.Latency
-                        << ", Inlining = " << Score << "}\n");
-
-      FunctionGrowth[F] += FuncSize - B.CodeSize;
-
-      auto IsProfitable = [](Bonus &B, unsigned Score, unsigned FuncSize,
-                             unsigned FuncGrowth) -> bool {
+      auto IsProfitable = [&]() -> bool {
         // No check required.
         if (ForceSpecialization)
           return true;
+
+        unsigned CodeSizeSavings = getCostValue(CodeSize);
+        // TODO: We should only accumulate codesize increase of specializations
+        // that are actually created.
+        FunctionGrowth[F] += FuncSize - CodeSizeSavings;
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hazzlim wrote:

> Hmm, but we sometimes early exit due to inlining bonus. Bummer

Yeah, it's somewhat annoying - I've put it where it is for this reason.

>Perhaps we can move it here ...

I think that this would be the ideal place to do the accumulation to `FunctionGrowth[F]`.

Could you clarify what you mean by the following:
> (it is S.Score as long as we remove Score += std::max(CodeSizeSavings, LatencySavings)). 

The Score is initially the Inlining Bonus, and then we add `std::max(CodeSizeSavings, LatencySavings))` - do you mean to just simply set `Score = CodeSizeSavings` in the case where we reach this point i.e. we are specializing due to CodeSizeSavings/LatencySavings rather than the Inlining Bonus?

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