Value num refine phis

src/coreclr/jit/assertionprop.cpp

@@ -1466,9 +1466,24 @@ AssertionIndex Compiler::optCreateAssertion(GenTree*         op1,
             assertion.op1.vn         = optConservativeNormalVN(op1);
             assertion.op1.lcl.ssaNum = op1->AsLclVarCommon()->GetSsaNum();
 
-            assert((assertion.op1.lcl.ssaNum == SsaConfig::RESERVED_SSA_NUM) ||
-                   (assertion.op1.vn == vnStore->VNConservativeNormalValue(
-                                            lvaGetDesc(lclNum)->GetPerSsaData(assertion.op1.lcl.ssaNum)->m_vnPair)));
+#ifdef DEBUG
+
+            // If we're ssa based, check that the VN is reasonable.
+            //
+            if (assertion.op1.lcl.ssaNum != SsaConfig::RESERVED_SSA_NUM)
+            {
+                LclSsaVarDsc* const ssaDsc = lvaGetDesc(lclNum)->GetPerSsaData(assertion.op1.lcl.ssaNum);
+
+                bool doesVNMatch = (assertion.op1.vn == vnStore->VNConservativeNormalValue(ssaDsc->m_vnPair));
+
+                if (!doesVNMatch && ssaDsc->m_updated)
+                {
+                    doesVNMatch = (assertion.op1.vn == vnStore->VNConservativeNormalValue(ssaDsc->m_origVNPair));
+                }
+
+                assert(doesVNMatch);
+            }
+#endif
 
             ssize_t      cnsValue  = 0;
             GenTreeFlags iconFlags = GTF_EMPTY;

src/coreclr/jit/compiler.h

@@ -311,6 +311,13 @@ class LclSsaVarDsc
     }
 
     ValueNumPair m_vnPair;
+
+#ifdef DEBUG
+    // True if this ssa def VN was updated
+    bool m_updated = false;
+    // Originally assigned VN
+    ValueNumPair m_origVNPair;
+#endif
 };
 
 // This class stores information associated with a memory SSA definition.
@@ -5701,9 +5708,15 @@ class Compiler
 
     // Utility functions for fgValueNumber.
 
+    // Value number a block or blocks in a loop
+    void fgValueNumberBlocks(BasicBlock* block, BlockSet& visitedBlocks);
+
     // Perform value-numbering for the trees in "blk".
     void fgValueNumberBlock(BasicBlock* blk);
 
+    // Value number a phi definition
+    void fgValueNumberPhiDef(GenTreeLclVar* newSsaDef, BasicBlock* block, bool isUpdate = false);
+
     // Requires that "entryBlock" is the header block of "loop" and that "loop" is the
     // innermost loop of which "entryBlock" is the entry.  Returns the value number that should be
     // assumed for the memoryKind at the start "entryBlk".

src/coreclr/jit/copyprop.cpp

@@ -161,11 +161,25 @@ bool Compiler::optCopyProp(
     assert((tree->gtFlags & GTF_VAR_DEF) == 0);
     assert(tree->GetLclNum() == lclNum);
 
-    bool       madeChanges = false;
-    LclVarDsc* varDsc      = lvaGetDesc(lclNum);
-    ValueNum   lclDefVN    = varDsc->GetPerSsaData(tree->GetSsaNum())->m_vnPair.GetConservative();
+    bool                madeChanges = false;
+    LclVarDsc* const    varDsc      = lvaGetDesc(lclNum);
+    LclSsaVarDsc* const varSsaDsc   = varDsc->GetPerSsaData(tree->GetSsaNum());
+    GenTree* const      varDefTree  = varSsaDsc->GetDefNode();
+    BasicBlock* const   varDefBlock = varSsaDsc->GetBlock();
+    ValueNum const      lclDefVN    = varSsaDsc->m_vnPair.GetConservative();
     assert(lclDefVN != ValueNumStore::NoVN);
 
+    // See if this local is a candidate for phi dev equivalence checks
+    //
+    bool const varDefTreeIsPhiDef             = (varDefTree != nullptr) && varDefTree->IsPhiDefn();
+    bool       varDefTreeIsPhiDefAtCycleEntry = false;
+
+    if (varDefTreeIsPhiDef)
+    {
+        FlowGraphNaturalLoop* const loop = m_blockToLoop->GetLoop(varDefBlock);
+        varDefTreeIsPhiDefAtCycleEntry   = (loop != nullptr) && (loop->GetHeader() == varDefBlock);
+    }
+
     for (LclNumToLiveDefsMap::Node* const iter : LclNumToLiveDefsMap::KeyValueIteration(curSsaName))
     {
         unsigned newLclNum = iter->GetKey();
@@ -190,7 +204,15 @@ bool Compiler::optCopyProp(
 
         if (newLclDefVN != lclDefVN)
         {
-            continue;
+            bool arePhiDefsEquivalent =
+                varDefTreeIsPhiDefAtCycleEntry && vnStore->AreVNsEquivalent(lclDefVN, newLclDefVN);
+            if (!arePhiDefsEquivalent)
+            {
+                continue;
+            }
+
+            JITDUMP("orig [%06] copy [%06u] VNs proved equivalent\n", dspTreeID(tree),
+                    dspTreeID(newLclDef.GetDefNode()));
         }
 
         // It may not be profitable to propagate a 'doNotEnregister' lclVar to an existing use of an
@@ -334,12 +356,6 @@ void Compiler::optCopyPropPushDef(GenTree* defNode, GenTreeLclVarCommon* lclNode
     else if (lclNode->HasSsaName())
     {
         unsigned ssaNum = lclNode->GetSsaNum();
-        if ((defNode != nullptr) && defNode->IsPhiDefn())
-        {
-            // TODO-CQ: design better heuristics for propagation and remove this.
-            ssaNum = SsaConfig::RESERVED_SSA_NUM;
-        }
-
         pushDef(lclNum, ssaNum);
     }
 }