[InlineCost] Consider the default branch when transforming to comparison

Author: dianqk

llvm/lib/Analysis/InlineCost.cpp

@@ -701,12 +701,14 @@ class InlineCostCallAnalyzer final : public CallAnalyzer {
 
   void onFinalizeSwitch(unsigned JumpTableSize, unsigned NumCaseCluster,
                         bool DefaultDestUndefined) override {
-    // if (!DefaultDestUndefined)
-    //   addCost(2 * InstrCost);
     // If suitable for a jump table, consider the cost for the table size and
     // branch to destination.
     // Maximum valid cost increased in this function.
     if (JumpTableSize) {
+      // Suppose a default branch includes one compare and one conditional
+      // branch if it's reachable.
+      if (!DefaultDestUndefined)
+        addCost(2 * InstrCost);
       int64_t JTCost =
           static_cast<int64_t>(JumpTableSize) * InstrCost + 4 * InstrCost;
       addCost(JTCost);
@@ -715,10 +717,13 @@ class InlineCostCallAnalyzer final : public CallAnalyzer {
 
     if (NumCaseCluster <= 3) {
       // Suppose a comparison includes one compare and one conditional branch.
-      addCost(NumCaseCluster * 2 * InstrCost);
+      // We can reduce a set of instructions if the default branch is
+      // undefined.
+      addCost((NumCaseCluster - DefaultDestUndefined) * 2 * InstrCost);
       return;
     }
 
+    // FIXME: Consider the case when default branch is undefined.
     int64_t ExpectedNumberOfCompare =
         getExpectedNumberOfCompare(NumCaseCluster);
     int64_t SwitchCost = ExpectedNumberOfCompare * 2 * InstrCost;
@@ -1235,11 +1240,10 @@ class InlineCostFeaturesAnalyzer final : public CallAnalyzer {
 
   void onFinalizeSwitch(unsigned JumpTableSize, unsigned NumCaseCluster,
                         bool DefaultDestUndefined) override {
-    // if (!DefaultDestUndefined)
-    //   increment(InlineCostFeatureIndex::switch_default_dest_penalty,
-    //             SwitchDefaultDestCostMultiplier * InstrCost);
-
     if (JumpTableSize) {
+      if (!DefaultDestUndefined)
+        increment(InlineCostFeatureIndex::switch_default_dest_penalty,
+                  SwitchDefaultDestCostMultiplier * InstrCost);
       int64_t JTCost = static_cast<int64_t>(JumpTableSize) * InstrCost +
                        JTCostMultiplier * InstrCost;
       increment(InlineCostFeatureIndex::jump_table_penalty, JTCost);
@@ -1248,10 +1252,12 @@ class InlineCostFeaturesAnalyzer final : public CallAnalyzer {
 
     if (NumCaseCluster <= 3) {
       increment(InlineCostFeatureIndex::case_cluster_penalty,
-                NumCaseCluster * CaseClusterCostMultiplier * InstrCost);
+                (NumCaseCluster - DefaultDestUndefined) *
+                    CaseClusterCostMultiplier * InstrCost);
       return;
     }
 
+    // FIXME: Consider the case when default branch is undefined.
     int64_t ExpectedNumberOfCompare =
         getExpectedNumberOfCompare(NumCaseCluster);