JIT: Change VN's representation for phi definitions (#105198)

Replace `VNF_PhiDef` and `VNF_MemoryPhiDef` by new explicit
representations that represent all phi args directly.

Author: jakobbotsch

src/coreclr/jit/optimizer.cpp

@@ -5162,24 +5162,13 @@ bool Compiler::optVNIsLoopInvariant(ValueNum vn, FlowGraphNaturalLoop* loop, VNS
         return previousRes;
     }
 
-    bool      res = true;
-    VNFuncApp funcApp;
+    bool           res = true;
+    VNFuncApp      funcApp;
+    VNPhiDef       phiDef;
+    VNMemoryPhiDef memoryPhiDef;
     if (vnStore->GetVNFunc(vn, &funcApp))
     {
-        if (funcApp.m_func == VNF_PhiDef)
-        {
-            // Is the definition within the loop?  If so, is not loop-invariant.
-            unsigned      lclNum = funcApp.m_args[0];
-            unsigned      ssaNum = funcApp.m_args[1];
-            LclSsaVarDsc* ssaDef = lvaTable[lclNum].GetPerSsaData(ssaNum);
-            res                  = !loop->ContainsBlock(ssaDef->GetBlock());
-        }
-        else if (funcApp.m_func == VNF_PhiMemoryDef)
-        {
-            BasicBlock* defnBlk = reinterpret_cast<BasicBlock*>(vnStore->ConstantValue<ssize_t>(funcApp.m_args[0]));
-            res                 = !loop->ContainsBlock(defnBlk);
-        }
-        else if (funcApp.m_func == VNF_MemOpaque)
+        if (funcApp.m_func == VNF_MemOpaque)
         {
             const unsigned loopIndex = funcApp.m_args[0];
 
@@ -5239,6 +5228,16 @@ bool Compiler::optVNIsLoopInvariant(ValueNum vn, FlowGraphNaturalLoop* loop, VNS
             }
         }
     }
+    else if (vnStore->GetPhiDef(vn, &phiDef))
+    {
+        // Is the definition within the loop?  If so, is not loop-invariant.
+        LclSsaVarDsc* ssaDef = lvaTable[phiDef.LclNum].GetPerSsaData(phiDef.SsaDef);
+        res                  = !loop->ContainsBlock(ssaDef->GetBlock());
+    }
+    else if (vnStore->GetMemoryPhiDef(vn, &memoryPhiDef))
+    {
+        res = !loop->ContainsBlock(memoryPhiDef.Block);
+    }
 
     loopVnInvariantCache->Set(vn, res);
     return res;

src/coreclr/jit/redundantbranchopts.cpp

@@ -1398,8 +1398,8 @@ bool Compiler::optJumpThreadPhi(BasicBlock* block, GenTree* tree, ValueNum treeN
     for (int i = 0; i < 2; i++)
     {
         const ValueNum phiDefVN = treeNormVNFuncApp.m_args[i];
-        VNFuncApp      phiDefFuncApp;
-        if (!vnStore->GetVNFunc(phiDefVN, &phiDefFuncApp) || (phiDefFuncApp.m_func != VNF_PhiDef))
+        VNPhiDef       phiDef;
+        if (!vnStore->GetPhiDef(phiDefVN, &phiDef))
         {
             // This input is not a phi def. If it's a func app it might depend on
             // transitively on a phi def; consider a general search utility.
@@ -1409,12 +1409,10 @@ bool Compiler::optJumpThreadPhi(BasicBlock* block, GenTree* tree, ValueNum treeN
 
         // The PhiDef args tell us which local and which SSA def of that local.
         //
-        assert(phiDefFuncApp.m_arity == 3);
-        const unsigned lclNum    = unsigned(phiDefFuncApp.m_args[0]);
-        const unsigned ssaDefNum = unsigned(phiDefFuncApp.m_args[1]);
-        const ValueNum phiVN     = ValueNum(phiDefFuncApp.m_args[2]);
-        JITDUMP("... JT-PHI [interestingVN] in " FMT_BB " relop %s operand VN is PhiDef for V%02u:%u " FMT_VN "\n",
-                block->bbNum, i == 0 ? "first" : "second", lclNum, ssaDefNum, phiVN);
+        const unsigned lclNum    = phiDef.LclNum;
+        const unsigned ssaDefNum = phiDef.SsaDef;
+        JITDUMP("... JT-PHI [interestingVN] in " FMT_BB " relop %s operand VN is PhiDef for V%02u\n", block->bbNum,
+                i == 0 ? "first" : "second", lclNum, ssaDefNum);
         if (!foundPhiDef)
         {
             DISPTREE(tree);