From cc58e8918b70d5698ec06c0b6e4c6e4c27971870 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Sat, 1 May 2021 17:40:26 +0200
Subject: [PATCH] [SCEV] Simplify backedge count clearing (NFC)

This seems to be a leftover from when the BackedgeTakenInfo
stored multiple exit counts with manual memory management. At
some point this was switchted to a simple vector, and there should
be no need to micro-manage the clearing anymore. We can simply
drop the loop from the map and the the destructor do its job.
---
 llvm/include/llvm/Analysis/ScalarEvolution.h |  3 ---
 llvm/lib/Analysis/ScalarEvolution.cpp        | 34 ++++++----------------------
 2 files changed, 7 insertions(+), 30 deletions(-)

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 414baac..e84b710 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1461,9 +1461,6 @@ private:
     /// Return true if any backedge taken count expressions refer to the given
     /// subexpression.
     bool hasOperand(const SCEV *S, ScalarEvolution *SE) const;
-
-    /// Invalidate this result and free associated memory.
-    void clear();
   };
 
   /// Cache the backedge-taken count of the loops for this function as they
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index f224ab2..4005597 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -7207,16 +7207,6 @@ void ScalarEvolution::forgetAllLoops() {
 }
 
 void ScalarEvolution::forgetLoop(const Loop *L) {
-  // Drop any stored trip count value.
-  auto RemoveLoopFromBackedgeMap =
-      [](DenseMap<const Loop *, BackedgeTakenInfo> &Map, const Loop *L) {
-        auto BTCPos = Map.find(L);
-        if (BTCPos != Map.end()) {
-          BTCPos->second.clear();
-          Map.erase(BTCPos);
-        }
-      };
-
   SmallVector<const Loop *, 16> LoopWorklist(1, L);
   SmallVector<Instruction *, 32> Worklist;
   SmallPtrSet<Instruction *, 16> Visited;
@@ -7225,8 +7215,9 @@ void ScalarEvolution::forgetLoop(const Loop *L) {
   while (!LoopWorklist.empty()) {
     auto *CurrL = LoopWorklist.pop_back_val();
 
-    RemoveLoopFromBackedgeMap(BackedgeTakenCounts, CurrL);
-    RemoveLoopFromBackedgeMap(PredicatedBackedgeTakenCounts, CurrL);
+    // Drop any stored trip count value.
+    BackedgeTakenCounts.erase(CurrL);
+    PredicatedBackedgeTakenCounts.erase(CurrL);
 
     // Drop information about predicated SCEV rewrites for this loop.
     for (auto I = PredicatedSCEVRewrites.begin();
@@ -7484,11 +7475,6 @@ ScalarEvolution::BackedgeTakenInfo::BackedgeTakenInfo(
          "No point in having a non-constant max backedge taken count!");
 }
 
-/// Invalidate this result and free the ExitNotTakenInfo array.
-void ScalarEvolution::BackedgeTakenInfo::clear() {
-  ExitNotTaken.clear();
-}
-
 /// Compute the number of times the backedge of the specified loop will execute.
 ScalarEvolution::BackedgeTakenInfo
 ScalarEvolution::computeBackedgeTakenCount(const Loop *L,
@@ -12227,13 +12213,8 @@ ScalarEvolution::~ScalarEvolution() {
   ExprValueMap.clear();
   ValueExprMap.clear();
   HasRecMap.clear();
-
-  // Free any extra memory created for ExitNotTakenInfo in the unlikely event
-  // that a loop had multiple computable exits.
-  for (auto &BTCI : BackedgeTakenCounts)
-    BTCI.second.clear();
-  for (auto &BTCI : PredicatedBackedgeTakenCounts)
-    BTCI.second.clear();
+  BackedgeTakenCounts.clear();
+  PredicatedBackedgeTakenCounts.clear();
 
   assert(PendingLoopPredicates.empty() && "isImpliedCond garbage");
   assert(PendingPhiRanges.empty() && "getRangeRef garbage");
@@ -12648,10 +12629,9 @@ ScalarEvolution::forgetMemoizedResults(const SCEV *S) {
       [S, this](DenseMap<const Loop *, BackedgeTakenInfo> &Map) {
         for (auto I = Map.begin(), E = Map.end(); I != E;) {
           BackedgeTakenInfo &BEInfo = I->second;
-          if (BEInfo.hasOperand(S, this)) {
-            BEInfo.clear();
+          if (BEInfo.hasOperand(S, this))
             Map.erase(I++);
-          } else
+          else
             ++I;
         }
       };
-- 
2.7.4