From 8a24e0cb5aeecef63fb77830e437bcc116985af1 Mon Sep 17 00:00:00 2001
From: Mircea Trofin <mtrofin@google.com>
Date: Mon, 26 Sep 2022 12:20:37 -0700
Subject: [PATCH] [nfc][mlgo] Lazily compute the regalloc reward

Differential Revision: https://reviews.llvm.org/D134664
---
 llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp | 25 ++++++++++++++++---------
 llvm/lib/CodeGen/RegAllocEvictionAdvisor.h  |  3 ++-
 llvm/lib/CodeGen/RegAllocPriorityAdvisor.h  |  3 ++-
 3 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp b/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp
index 86c28ab..e48aac4 100644
--- a/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp
+++ b/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp
@@ -461,9 +461,10 @@ public:
     return I->second.get();
   }
 
-  void logRewardIfNeeded(const MachineFunction &MF, float Reward) override {
+  void logRewardIfNeeded(const MachineFunction &MF,
+                         llvm::function_ref<float()> GetReward) override {
     if (auto *Log = this->getLogger(MF))
-      Log->logFloatFinalReward(Reward);
+      Log->logFloatFinalReward(GetReward());
   }
 
 private:
@@ -1067,13 +1068,19 @@ int64_t DevelopmentModeEvictAdvisor::tryFindEvictionCandidatePosition(
 }
 
 bool RegAllocScoring::runOnMachineFunction(MachineFunction &MF) {
-  float Reward = static_cast<float>(
-      calculateRegAllocScore(MF, getAnalysis<MachineBlockFrequencyInfo>())
-          .getScore());
-
-  getAnalysis<RegAllocEvictionAdvisorAnalysis>().logRewardIfNeeded(MF, Reward);
-  getAnalysis<RegAllocPriorityAdvisorAnalysis>().logRewardIfNeeded(MF, Reward);
-
+  Optional<float> CachedReward;
+  auto GetReward = [&]() {
+    if (!CachedReward)
+      CachedReward = static_cast<float>(
+          calculateRegAllocScore(MF, getAnalysis<MachineBlockFrequencyInfo>())
+              .getScore());
+    return *CachedReward;
+  };
+
+  getAnalysis<RegAllocEvictionAdvisorAnalysis>().logRewardIfNeeded(MF,
+                                                                   GetReward);
+  getAnalysis<RegAllocPriorityAdvisorAnalysis>().logRewardIfNeeded(MF,
+                                                                   GetReward);
   return false;
 }
 #endif // #ifdef LLVM_HAVE_TF_API
diff --git a/llvm/lib/CodeGen/RegAllocEvictionAdvisor.h b/llvm/lib/CodeGen/RegAllocEvictionAdvisor.h
index c7f48bc..a3936ea 100644
--- a/llvm/lib/CodeGen/RegAllocEvictionAdvisor.h
+++ b/llvm/lib/CodeGen/RegAllocEvictionAdvisor.h
@@ -177,7 +177,8 @@ public:
   virtual std::unique_ptr<RegAllocEvictionAdvisor>
   getAdvisor(const MachineFunction &MF, const RAGreedy &RA) = 0;
   AdvisorMode getAdvisorMode() const { return Mode; }
-  virtual void logRewardIfNeeded(const MachineFunction &MF, float Reward){};
+  virtual void logRewardIfNeeded(const MachineFunction &MF,
+                                 llvm::function_ref<float()> GetReward){};
 
 protected:
   // This analysis preserves everything, and subclasses may have additional
diff --git a/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h b/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h
index 520d8d8..1e9fa96 100644
--- a/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h
+++ b/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h
@@ -68,7 +68,8 @@ public:
   virtual std::unique_ptr<RegAllocPriorityAdvisor>
   getAdvisor(const MachineFunction &MF, const RAGreedy &RA) = 0;
   AdvisorMode getAdvisorMode() const { return Mode; }
-  virtual void logRewardIfNeeded(const MachineFunction &MF, float Reward){};
+  virtual void logRewardIfNeeded(const MachineFunction &MF,
+                                 llvm::function_ref<float()> GetReward){};
 
 protected:
   // This analysis preserves everything, and subclasses may have additional
-- 
2.7.4