JIT: add concept of edge likelihood (#81738)

Now that FlowEdges are created early and persist, decorate them with likelihood
information early, if we have edge-based PGO data.

We don't use the likelihood for anything yet, but I need to get it in circulation
so I can start working on refining both initial and subsequent consistency of
the data.

Also add a diagnostic checker for likelhood, and a way to enable it. All of
this is off by default.

Author: AndyAyersMS

src/coreclr/jit/block.h

@@ -1800,12 +1800,25 @@ struct FlowEdge
     weight_t m_edgeWeightMin;
     weight_t m_edgeWeightMax;
 
+    // Likelihood that m_sourceBlock transfers control along this edge.
+    // Values in range [0..1]
+    weight_t m_likelihood;
+
     // The count of duplicate "edges" (used for switch stmts or degenerate branches)
     unsigned m_dupCount;
 
+#ifdef DEBUG
+    bool m_likelihoodSet;
+#endif
+
 public:
     FlowEdge(BasicBlock* block, FlowEdge* rest)
-        : m_nextPredEdge(rest), m_sourceBlock(block), m_edgeWeightMin(0), m_edgeWeightMax(0), m_dupCount(0)
+        : m_nextPredEdge(rest)
+        , m_sourceBlock(block)
+        , m_edgeWeightMin(0)
+        , m_edgeWeightMax(0)
+        , m_likelihood(0)
+        , m_dupCount(0) DEBUGARG(m_likelihoodSet(false))
     {
     }
 
@@ -1852,6 +1865,32 @@ struct FlowEdge
     bool setEdgeWeightMaxChecked(weight_t newWeight, BasicBlock* bDst, weight_t slop, bool* wbUsedSlop);
     void setEdgeWeights(weight_t newMinWeight, weight_t newMaxWeight, BasicBlock* bDst);
 
+    weight_t getLikelihood() const
+    {
+        return m_likelihood;
+    }
+
+    void setLikelihood(weight_t likelihood)
+    {
+        assert(likelihood >= 0.0);
+        assert(likelihood <= 1.0);
+        INDEBUG(m_likelihoodSet = true);
+        m_likelihood = likelihood;
+    }
+
+#ifdef DEBUG
+    bool hasLikelihood() const
+    {
+        return m_likelihoodSet;
+    }
+#endif
+
+    weight_t getLikelyWeight() const
+    {
+        assert(m_likelihoodSet);
+        return m_likelihood * m_sourceBlock->bbWeight;
+    }
+
     unsigned getDupCount() const
     {
         return m_dupCount;

src/coreclr/jit/compiler.cpp

@@ -4434,6 +4434,7 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     // Note: the importer is sensitive to block weights, so this has
     // to happen before importation.
     //
+    activePhaseChecks |= PhaseChecks::CHECK_PROFILE;
     DoPhase(this, PHASE_INCPROFILE, &Compiler::fgIncorporateProfileData);
 
     // If we're going to instrument code, we may need to prepare before
@@ -4453,8 +4454,8 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
 
     // Enable the post-phase checks that use internal logic to decide when checking makes sense.
     //
-    activePhaseChecks |= PhaseChecks::CHECK_EH | PhaseChecks::CHECK_LOOPS | PhaseChecks::CHECK_UNIQUE |
-                         PhaseChecks::CHECK_PROFILE | PhaseChecks::CHECK_LINKED_LOCALS;
+    activePhaseChecks |=
+        PhaseChecks::CHECK_EH | PhaseChecks::CHECK_LOOPS | PhaseChecks::CHECK_UNIQUE | PhaseChecks::CHECK_LINKED_LOCALS;
 
     // Import: convert the instrs in each basic block to a tree based intermediate representation
     //

src/coreclr/jit/fgbasic.cpp

@@ -488,7 +488,7 @@ void Compiler::fgReplaceSwitchJumpTarget(BasicBlock* blockSwitch, BasicBlock* ne
             //
             FlowEdge* const newEdge = fgAddRefPred(newTarget, blockSwitch);
 
-            // Now set the correct value of newEdge's lDupCount
+            // Now set the correct value of newEdge's DupCount
             // and replace any other jumps in jumpTab[] that go to oldTarget.
             //
             i++;

src/coreclr/jit/fgdiagnostic.cpp

@@ -3635,7 +3635,7 @@ void Compiler::fgDebugCheckBlockLinks()
             {
                 // Create a set with all the successors. Don't use BlockSet, so we don't need to worry
                 // about the BlockSet epoch.
-                BitVecTraits bitVecTraits(fgBBNumMax + 1, this);
+                BitVecTraits bitVecTraits(impInlineRoot()->fgBBNumMax + 1, this);
                 BitVec       succBlocks(BitVecOps::MakeEmpty(&bitVecTraits));
                 for (BasicBlock* const bTarget : block->SwitchTargets())
                 {