[compiler] Optimize BranchConditionDuplicationPhase

Only apply this optimization to the conditions that have multiple
branch uses.

Bug: v8:12484
Change-Id: Ieb74b8e879e62aa96344f2903f1fea6a1b769549
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3902559Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Hao A Xu <hao.a.xu@intel.com>
Cr-Commit-Position: refs/heads/main@{#83347}

src/compiler/branch-condition-duplicator.cc

@@ -70,7 +70,7 @@ void BranchConditionDuplicator::DuplicateConditionIfNeeded(Node* node) {
   if (!IsBranch(node)) return;
 
   Node* condNode = node->InputAt(0);
-  if (condNode->UseCount() > 1 && CanDuplicate(condNode)) {
+  if (condNode->BranchUseCount() > 1 && CanDuplicate(condNode)) {
     node->ReplaceInput(0, DuplicateNode(condNode));
   }
 }

src/compiler/node.cc

@@ -293,6 +293,15 @@ int Node::UseCount() const {
   return use_count;
 }
 
+int Node::BranchUseCount() const {
+  int use_count = 0;
+  for (Use* use = first_use_; use; use = use->next) {
+    if (use->from()->opcode() == IrOpcode::kBranch) {
+      ++use_count;
+    }
+  }
+  return use_count;
+}
 
 void Node::ReplaceUses(Node* that) {
   DCHECK(this->first_use_ == nullptr || this->first_use_->prev == nullptr);

src/compiler/node.h

@@ -98,6 +98,7 @@ class V8_EXPORT_PRIVATE Node final {
   void EnsureInputCount(Zone* zone, int new_input_count);
 
   int UseCount() const;
+  int BranchUseCount() const;
   void ReplaceUses(Node* replace_to);
 
   class InputEdges;