From 4282e32712da220fd97177772e22ec1ee7e50af2 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 29 Aug 2010 17:46:00 +0000
Subject: [PATCH] rework the ownership of subloop alias information: instead of
 keeping them around until the pass is destroyed, keep them around a) just
 when useful (not for outer loops) and b) destroy them right after we use
 them.  This should reduce memory use and fixes potential bugs where a loop is
 deleted and another loop gets allocated to the same address.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112446 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LICM.cpp | 41 +++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 16 deletions(-)

diff --git a/lib/Transforms/Scalar/LICM.cpp b/lib/Transforms/Scalar/LICM.cpp
index d8b46bbc358..44dfed8ed4e 100644
--- a/lib/Transforms/Scalar/LICM.cpp
+++ b/lib/Transforms/Scalar/LICM.cpp
@@ -84,27 +84,21 @@ namespace {
     }
 
     bool doFinalization() {
-      // Free the values stored in the map
-      for (std::map<Loop *, AliasSetTracker *>::iterator
-             I = LoopToAliasMap.begin(), E = LoopToAliasMap.end(); I != E; ++I)
-        delete I->second;
-
-      LoopToAliasMap.clear();
+      assert(LoopToAliasSetMap.empty() && "Didn't free loop alias sets");
       return false;
     }
 
   private:
-    // Various analyses that we use...
     AliasAnalysis *AA;       // Current AliasAnalysis information
     LoopInfo      *LI;       // Current LoopInfo
     DominatorTree *DT;       // Dominator Tree for the current Loop.
 
-    // State that is updated as we process loops
+    // State that is updated as we process loops.
     bool Changed;            // Set to true when we change anything.
     BasicBlock *Preheader;   // The preheader block of the current loop...
     Loop *CurLoop;           // The current loop we are working on...
     AliasSetTracker *CurAST; // AliasSet information for the current loop...
-    std::map<Loop *, AliasSetTracker *> LoopToAliasMap;
+    DenseMap<Loop*, AliasSetTracker*> LoopToAliasSetMap;
 
     /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
     void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L);
@@ -223,15 +217,20 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
   DT = &getAnalysis<DominatorTree>();
 
   CurAST = new AliasSetTracker(*AA);
-  // Collect Alias info from subloops
+  // Collect Alias info from subloops.
   for (Loop::iterator LoopItr = L->begin(), LoopItrE = L->end();
        LoopItr != LoopItrE; ++LoopItr) {
     Loop *InnerL = *LoopItr;
-    AliasSetTracker *InnerAST = LoopToAliasMap[InnerL];
-    assert (InnerAST && "Where is my AST?");
+    AliasSetTracker *InnerAST = LoopToAliasSetMap[InnerL];
+    assert(InnerAST && "Where is my AST?");
 
     // What if InnerLoop was modified by other passes ?
     CurAST->add(*InnerAST);
+    
+    // Once we've incorporated the inner loop's AST into ours, we don't need the
+    // subloop's anymore.
+    delete InnerAST;
+    LoopToAliasSetMap.erase(InnerL);
   }
   
   CurLoop = L;
@@ -246,7 +245,7 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
   for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
        I != E; ++I) {
     BasicBlock *BB = *I;
-    if (LI->getLoopFor(BB) == L)        // Ignore blocks in subloops...
+    if (LI->getLoopFor(BB) == L)        // Ignore blocks in subloops.
       CurAST->add(*BB);                 // Incorporate the specified basic block
   }
 
@@ -278,7 +277,12 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
   CurLoop = 0;
   Preheader = 0;
 
-  LoopToAliasMap[L] = CurAST;
+  // If this loop is nested inside of another one, save the alias information
+  // for when we process the outer loop.
+  if (L->getParentLoop())
+    LoopToAliasSetMap[L] = CurAST;
+  else
+    delete CurAST;
   return Changed;
 }
 
@@ -473,6 +477,11 @@ void LICM::sink(Instruction &I) {
       I.removeFromParent();
       BasicBlock::iterator InsertPt = ExitBlocks[0]->getFirstNonPHI();
       ExitBlocks[0]->getInstList().insert(InsertPt, &I);
+
+      // This instruction is no longer in the AST for the current loop, because
+      // we just sunk it out of the loop.  If we just sunk it into an outer
+      // loop, we will rediscover the operation when we process it.
+      CurAST->deleteValue(&I);
     }
     return;
   }
@@ -842,7 +851,7 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
 
 /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
 void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
-  AliasSetTracker *AST = LoopToAliasMap[L];
+  AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
   if (!AST)
     return;
 
@@ -852,7 +861,7 @@ void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
 /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
 /// set.
 void LICM::deleteAnalysisValue(Value *V, Loop *L) {
-  AliasSetTracker *AST = LoopToAliasMap[L];
+  AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
   if (!AST)
     return;