Deleting field sequences from LCL_FLD and VNF_PtrToArrElem (#68986)

* Delete field sequences from GenTreeLclFld

* Delete field sequences from VNF_PtrToArrElem

* Clean up "DefinesLocalAddr"

Move the responsibility of determining "entireness" to
its only caller that needed to do that: "DefinesLocal".

Add function headers.

No diffs.

* Also clean up block morphing a little

No diffs.

* Fix a potential bug with return buffer numbering

Also address the TODO-CQ.

* Fix another "VN maintainance in morph" bug

Exposed by the more aggressive hoisting.

src/coreclr/jit/compiler.h

@@ -471,8 +471,6 @@ class LclVarDsc
     unsigned char lvInSsa : 1;       // The variable is in SSA form (set by SsaBuilder)
     unsigned char lvIsCSE : 1;       // Indicates if this LclVar is a CSE variable.
     unsigned char lvHasLdAddrOp : 1; // has ldloca or ldarga opcode on this local.
-    unsigned char lvStackByref : 1;  // This is a compiler temporary of TYP_BYREF that is known to point into our local
-                                     // stack frame.
 
     unsigned char lvHasILStoreOp : 1;         // there is at least one STLOC or STARG on this local
     unsigned char lvHasMultipleILStoreOp : 1; // there is more than one STLOC on this local
@@ -4782,8 +4780,6 @@ class Compiler
     // Does value-numbering for a block assignment.
     void fgValueNumberBlockAssignment(GenTree* tree);
 
-    bool fgValueNumberBlockAssignmentTypeCheck(LclVarDsc* dstVarDsc, FieldSeqNode* dstFldSeq, GenTree* src);
-
     // Does value-numbering for a cast tree.
     void fgValueNumberCastTree(GenTree* tree);
 
@@ -5702,8 +5698,6 @@ class Compiler
     GenTree* fgMorphMultiOp(GenTreeMultiOp* multiOp);
     GenTree* fgMorphConst(GenTree* tree);
 
-    bool fgMorphCanUseLclFldForCopy(unsigned lclNum1, unsigned lclNum2);
-
     GenTreeLclVar* fgMorphTryFoldObjAsLclVar(GenTreeObj* obj, bool destroyNodes = true);
     GenTreeOp* fgMorphCommutative(GenTreeOp* tree);
     GenTree* fgMorphCastedBitwiseOp(GenTreeOp* tree);

src/coreclr/jit/compiler.hpp

@@ -1348,7 +1348,7 @@ inline void GenTree::SetOper(genTreeOps oper, ValueNumberUpdate vnUpdate)
 #endif
         case GT_LCL_FLD:
             AsLclFld()->SetLclOffs(0);
-            AsLclFld()->SetFieldSeq(FieldSeqStore::NotAField());
+            AsLclFld()->SetLayout(nullptr);
             break;
 
         case GT_CALL:

src/coreclr/jit/decomposelongs.cpp

@@ -366,11 +366,9 @@ GenTree* DecomposeLongs::DecomposeLclVar(LIR::Use& use)
         m_compiler->lvaSetVarDoNotEnregister(varNum DEBUGARG(DoNotEnregisterReason::LocalField));
         loResult->SetOper(GT_LCL_FLD);
         loResult->AsLclFld()->SetLclOffs(0);
-        loResult->AsLclFld()->SetFieldSeq(FieldSeqStore::NotAField());
 
         hiResult->SetOper(GT_LCL_FLD);
         hiResult->AsLclFld()->SetLclOffs(4);
-        hiResult->AsLclFld()->SetFieldSeq(FieldSeqStore::NotAField());
     }
 
     return FinalizeDecomposition(use, loResult, hiResult, hiResult);

src/coreclr/jit/flowgraph.cpp

@@ -961,13 +961,6 @@ bool Compiler::fgAddrCouldBeNull(GenTree* addr)
         {
             return false;
         }
-
-        LclVarDsc* varDsc = lvaGetDesc(varNum);
-
-        if (varDsc->lvStackByref)
-        {
-            return false;
-        }
     }
     else if (addr->gtOper == GT_ADDR)
     {

src/coreclr/jit/gcinfo.cpp

@@ -346,25 +346,6 @@ GCInfo::WriteBarrierForm GCInfo::gcWriteBarrierFormFromTargetAddress(GenTree* tg
         return GCInfo::WBF_NoBarrier;
     }
 
-    if (tgtAddr->OperGet() == GT_LCL_VAR)
-    {
-        unsigned   lclNum = tgtAddr->AsLclVar()->GetLclNum();
-        LclVarDsc* varDsc = compiler->lvaGetDesc(lclNum);
-
-        // Instead of marking LclVar with 'lvStackByref',
-        // Consider decomposing the Value Number given to this LclVar to see if it was
-        // created using a GT_ADDR(GT_LCLVAR)  or a GT_ADD( GT_ADDR(GT_LCLVAR), Constant)
-
-        // We may have an internal compiler temp created in fgMorphCopyBlock() that we know
-        // points at one of our stack local variables, it will have lvStackByref set to true.
-        //
-        if (varDsc->lvStackByref)
-        {
-            assert(varDsc->TypeGet() == TYP_BYREF);
-            return GCInfo::WBF_NoBarrier;
-        }
-    }
-
     if (tgtAddr->TypeGet() == TYP_REF)
     {
         return GCInfo::WBF_BarrierUnchecked;