[llvm] [CodeLayout] Faster basic block reordering, ext-tsp (PR #68617)

[Fangrui Song via llvm-commits]

================
@@ -851,36 +880,42 @@ class ExtTSPImpl {
     Gain.updateIfLessThan(
         computeMergeGain(ChainPred, ChainSucc, Jumps, 0, MergeTypeT::X_Y));
 
-    if (EnableChainSplitAlongJumps) {
-      // Attach (a part of) ChainPred before the first node of ChainSucc.
-      for (JumpT *Jump : ChainSucc->Nodes.front()->InJumps) {
-        const NodeT *SrcBlock = Jump->Source;
-        if (SrcBlock->CurChain != ChainPred)
-          continue;
-        size_t Offset = SrcBlock->CurIndex + 1;
-        tryChainMerging(Offset, {MergeTypeT::X1_Y_X2, MergeTypeT::X2_X1_Y});
-      }
+    // Attach (a part of) ChainPred before the first node of ChainSucc.
+    for (JumpT *Jump : ChainSucc->Nodes.front()->InJumps) {
+      const NodeT *SrcBlock = Jump->Source;
+      if (SrcBlock->CurChain != ChainPred)
+        continue;
+      size_t Offset = SrcBlock->CurIndex + 1;
+      tryChainMerging(Offset, {MergeTypeT::X1_Y_X2, MergeTypeT::X2_X1_Y});
+    }
 
-      // Attach (a part of) ChainPred after the last node of ChainSucc.
-      for (JumpT *Jump : ChainSucc->Nodes.back()->OutJumps) {
-        const NodeT *DstBlock = Jump->Target;
-        if (DstBlock->CurChain != ChainPred)
-          continue;
-        size_t Offset = DstBlock->CurIndex;
-        tryChainMerging(Offset, {MergeTypeT::X1_Y_X2, MergeTypeT::Y_X2_X1});
-      }
+    // Attach (a part of) ChainPred after the last node of ChainSucc.
+    for (JumpT *Jump : ChainSucc->Nodes.back()->OutJumps) {
+      const NodeT *DstBlock = Jump->Target;
+      if (DstBlock->CurChain != ChainPred)
+        continue;
+      size_t Offset = DstBlock->CurIndex;
+      tryChainMerging(Offset, {MergeTypeT::X1_Y_X2, MergeTypeT::Y_X2_X1});
     }
 
-    // Try to break ChainPred in various ways and concatenate with ChainSucc.
     if (ChainPred->Nodes.size() <= ChainSplitThreshold) {
+      // Try to break ChainPred in various ways and concatenate with ChainSucc.
----------------
MaskRay wrote:

This comment move seems unnecessary.

https://github.com/llvm/llvm-project/pull/68617