Pick region info for LeaveNull block from finally label.

When there are infinite loops, we add edges from loop top to LeaveNull label, to avoid unreachable block removal phase deleting LeaveNull block.
When such edges are present, we will pick up wrong region info from the predecessor. So use the map.

lib/Backend/FlowGraph.cpp

@@ -173,6 +173,7 @@ FlowGraph::Build(void)
         this->finallyLabelStack = JitAnew(this->alloc, SList<IR::LabelInstr*>, this->alloc);
         this->leaveNullLabelStack = JitAnew(this->alloc, SList<IR::LabelInstr*>, this->alloc);
         this->regToFinallyEndMap = JitAnew(this->alloc, RegionToFinallyEndMapType, this->alloc, 0);
+        this->leaveNullLabelToFinallyLabelMap = JitAnew(this->alloc, LeaveNullLabelToFinallyLabelMapType, this->alloc, 0);
     }
 
     IR::Instr * currLastInstr = nullptr;
@@ -301,7 +302,8 @@ FlowGraph::Build(void)
 
             this->finallyLabelStack->Push(finallyLabel);
             Assert(!this->leaveNullLabelStack->Empty());
-            this->leaveNullLabelStack->Pop();
+            IR::LabelInstr * leaveNullLabel = this->leaveNullLabelStack->Pop();
+            this->leaveNullLabelToFinallyLabelMap->Item(leaveNullLabel, leaveTarget /*new finally label*/);
 
             Assert(leaveTarget->labelRefs.HasOne());
             IR::BranchInstr * brOnException = IR::BranchInstr::New(Js::OpCode::BrOnException, finallyLabel, instr->m_func);
@@ -671,6 +673,13 @@ void FlowGraph::InsertEdgeFromFinallyToEarlyExit(BasicBlock *finallyEndBlock, IR
     IR::LabelInstr *leaveLabel = IR::LabelInstr::New(Js::OpCode::Label, this->func);
     lastInstr->InsertBefore(leaveLabel);
 
+    if (this->leaveNullLabelToFinallyLabelMap->ContainsKey(finallyEndBlock->GetFirstInstr()->AsLabelInstr()))
+    {
+        // Add new LeaveNull label to the map, we don't delete old LeaveNull label from the map
+        Assert(this->leaveNullLabelToFinallyLabelMap->ContainsKey(finallyEndBlock->GetFirstInstr()->AsLabelInstr()));
+        this->leaveNullLabelToFinallyLabelMap->Item(leaveLabel, this->leaveNullLabelToFinallyLabelMap->Item(finallyEndBlock->GetFirstInstr()->AsLabelInstr()));
+    }
+
     this->AddBlock(leaveLabel, lastInstr, nextBB, finallyEndBlock /*prevBlock*/);
     leaveLabel->SetRegion(lastLabel->GetRegion());
 
@@ -1875,41 +1884,18 @@ FlowGraph::UpdateRegionForBlock(BasicBlock * block)
         // Head of the graph: create the root region.
         region = Region::New(RegionTypeRoot, nullptr, this->func);
     }
-    else if (block->GetLastInstr()->m_opcode == Js::OpCode::LeaveNull)
+    else if (this->leaveNullLabelToFinallyLabelMap && block->GetLastInstr()->m_opcode == Js::OpCode::LeaveNull)
     {
-        region = nullptr;
-        if (block->GetPredList()->Count() == 1)
-        {
-            FOREACH_PREDECESSOR_BLOCK(predBlock, block)
-            {
-                AssertMsg(predBlock->GetBlockNum() < this->blockCount, "Misnumbered block at teardown time?");
-                predRegion = predBlock->GetFirstInstr()->AsLabelInstr()->GetRegion();
-                if (predRegion)
-                {
-                    region = this->PropagateRegionFromPred(block, predBlock, predRegion, tryInstr);
-                    break;
-                }
-            }
-            NEXT_PREDECESSOR_BLOCK;
-        }
-        else
-        {
-            FOREACH_PREDECESSOR_BLOCK(predBlock, block)
-            {
-                AssertMsg(predBlock->GetBlockNum() < this->blockCount, "Misnumbered block at teardown time?");
-                predRegion = predBlock->GetFirstInstr()->AsLabelInstr()->GetRegion();
-                if (predRegion && predRegion->GetType() == RegionTypeFinally)
-                {
-                    region = this->PropagateRegionFromPred(block, predBlock, predRegion, tryInstr);
-                    break;
-                }
-            }
-            NEXT_PREDECESSOR_BLOCK;
-        }
-        if (this->regToFinallyEndMap)
-        {
-            regToFinallyEndMap->Item(region, block);
-        }
+        // We hold on to the LeaveNull block by adding BrOnException from loop tops
+        // So that LeaveNull doesn't get removed due to unreachable block elimination
+        // We need the finally end block to insert edge from finally to early exit
+        // If a LeaveNull block had only BrOnException edges from predecessor
+        // We will end up in inaccurate region propagation if we propagate from the predecessor edges
+        // So pick up the finally region from the map
+        Assert(this->leaveNullLabelToFinallyLabelMap->ContainsKey(block->GetFirstInstr()->AsLabelInstr()));
+        IR::LabelInstr * finallyLabel = this->leaveNullLabelToFinallyLabelMap->Item(block->GetFirstInstr()->AsLabelInstr());
+        Assert(finallyLabel);
+        region = finallyLabel->GetRegion();
     }
     else
     {
@@ -1981,6 +1967,19 @@ FlowGraph::UpdateRegionForBlockFromEHPred(BasicBlock * block, bool reassign)
         // Head of the graph: create the root region.
         region = Region::New(RegionTypeRoot, nullptr, this->func);
     }
+    else if (this->leaveNullLabelToFinallyLabelMap && block->GetLastInstr()->m_opcode == Js::OpCode::LeaveNull)
+    {
+        // We hold on to the LeaveNull block by adding BrOnException from loop tops
+        // So that LeaveNull doesn't get removed due to unreachable block elimination
+        // We need the finally end block to insert edge from finally to early exit
+        // If a LeaveNull block had only BrOnException edges from predecessor
+        // We will end up in inaccurate region propagation if we propagate from the predecessor edges
+        // So pick up the finally region from the map
+        Assert(this->leaveNullLabelToFinallyLabelMap->ContainsKey(block->GetFirstInstr()->AsLabelInstr()));
+        IR::LabelInstr * finallyLabel = this->leaveNullLabelToFinallyLabelMap->Item(block->GetFirstInstr()->AsLabelInstr());
+        Assert(finallyLabel);
+        region = finallyLabel->GetRegion();
+    }
     else
     {
         // Propagate the region forward by finding a predecessor we've already processed.

lib/Backend/FlowGraph.h

@@ -142,6 +142,7 @@ public:
         finallyLabelStack(nullptr),
         leaveNullLabelStack(nullptr),
         regToFinallyEndMap(nullptr),
+        leaveNullLabelToFinallyLabelMap(nullptr),
         hasBackwardPassInfo(false),
         hasLoop(false),
         implicitCallFlags(Js::ImplicitCall_HasNoInfo)
@@ -188,6 +189,8 @@ public:
     SList<IR::LabelInstr*> *  leaveNullLabelStack;
     typedef JsUtil::BaseDictionary<Region *, BasicBlock *, JitArenaAllocator> RegionToFinallyEndMapType;
     RegionToFinallyEndMapType * regToFinallyEndMap;
+    typedef JsUtil::BaseDictionary<IR::LabelInstr *, IR::LabelInstr *, JitArenaAllocator> LeaveNullLabelToFinallyLabelMapType;
+    LeaveNullLabelToFinallyLabelMapType * leaveNullLabelToFinallyLabelMap;
     bool                      hasBackwardPassInfo;
     bool                      hasLoop;
     Js::ImplicitCallFlags     implicitCallFlags;