JIT: Expand flow graph debug checking (#99238)

Ensure that the derived flow graph annotations, like loops and the
dominator tree, do not lose their link with the current DFS tree.

src/coreclr/jit/compiler.h

@@ -2323,6 +2323,11 @@ class FlowGraphDominatorTree
 
     static BasicBlock* IntersectDom(BasicBlock* block1, BasicBlock* block2);
 public:
+    const FlowGraphDfsTree* GetDfsTree()
+    {
+        return m_dfsTree;
+    }
+
     BasicBlock* Intersect(BasicBlock* block, BasicBlock* block2);
     bool Dominates(BasicBlock* dominator, BasicBlock* dominated);
 
@@ -2357,23 +2362,28 @@ class BlockToNaturalLoopMap
 // exceptional flow, then CanReach returns false.
 class BlockReachabilitySets
 {
-    FlowGraphDfsTree* m_dfsTree;
+    const FlowGraphDfsTree* m_dfsTree;
     BitVec* m_reachabilitySets;
 
-    BlockReachabilitySets(FlowGraphDfsTree* dfsTree, BitVec* reachabilitySets)
+    BlockReachabilitySets(const FlowGraphDfsTree* dfsTree, BitVec* reachabilitySets)
         : m_dfsTree(dfsTree)
         , m_reachabilitySets(reachabilitySets)
     {
     }
 
 public:
+    const FlowGraphDfsTree* GetDfsTree()
+    {
+        return m_dfsTree;
+    }
+
     bool CanReach(BasicBlock* from, BasicBlock* to);
 
 #ifdef DEBUG
     void Dump();
 #endif
 
-    static BlockReachabilitySets* Build(FlowGraphDfsTree* dfsTree);
+    static BlockReachabilitySets* Build(const FlowGraphDfsTree* dfsTree);
 };
 
 enum class FieldKindForVN
@@ -6095,7 +6105,7 @@ class Compiler
     bool fgDebugCheckIncomingProfileData(BasicBlock* block, ProfileChecks checks);
     bool fgDebugCheckOutgoingProfileData(BasicBlock* block, ProfileChecks checks);
 
-    void fgDebugCheckDfsTree();
+    void fgDebugCheckFlowGraphAnnotations();
 
 #endif // DEBUG
 

src/coreclr/jit/fgdiagnostic.cpp

@@ -4744,10 +4744,17 @@ void Compiler::fgDebugCheckLoops()
 }
 
 //------------------------------------------------------------------------------
-// fgDebugCheckDfsTree: Checks that the DFS tree matches the current flow graph.
+// fgDebugCheckFlowGraphAnnotations: Checks that all flow graph annotations
+// that are currently non-null are valid.
 //
-void Compiler::fgDebugCheckDfsTree()
+void Compiler::fgDebugCheckFlowGraphAnnotations()
 {
+    if (m_dfsTree == nullptr)
+    {
+        assert((m_loops == nullptr) && (m_domTree == nullptr) && (m_reachabilitySets == nullptr));
+        return;
+    }
+
     unsigned count =
         fgRunDfs([](BasicBlock* block, unsigned preorderNum) { assert(block->bbPreorderNum == preorderNum); },
                  [=](BasicBlock* block, unsigned postorderNum) {
@@ -4757,6 +4764,10 @@ void Compiler::fgDebugCheckDfsTree()
                  [](BasicBlock* block, BasicBlock* succ) {});
 
     assert(m_dfsTree->GetPostOrderCount() == count);
+
+    assert((m_loops == nullptr) || (m_loops->GetDfsTree() == m_dfsTree));
+    assert((m_domTree == nullptr) || (m_domTree->GetDfsTree() == m_dfsTree));
+    assert((m_reachabilitySets == nullptr) || (m_reachabilitySets->GetDfsTree() == m_dfsTree));
 }
 
 /*****************************************************************************/

src/coreclr/jit/flowgraph.cpp

@@ -6144,7 +6144,7 @@ BlockToNaturalLoopMap* BlockToNaturalLoopMap::Build(FlowGraphNaturalLoops* loops
 //   This algorithm consumes O(n^2) memory because we're using dense
 //   bitsets to represent reachability.
 //
-BlockReachabilitySets* BlockReachabilitySets::Build(FlowGraphDfsTree* dfsTree)
+BlockReachabilitySets* BlockReachabilitySets::Build(const FlowGraphDfsTree* dfsTree)
 {
     Compiler*    comp            = dfsTree->GetCompiler();
     BitVecTraits postOrderTraits = dfsTree->PostOrderTraits();

src/coreclr/jit/phase.cpp

@@ -171,10 +171,7 @@ void Phase::PostPhase(PhaseStatus status)
             comp->fgDebugCheckLinkedLocals();
         }
 
-        if (comp->m_dfsTree != nullptr)
-        {
-            comp->fgDebugCheckDfsTree();
-        }
+        comp->fgDebugCheckFlowGraphAnnotations();
     }
 #endif // DEBUG
 }