Delete "lvOverlappingFields" (#72356)

We used to exclude locals with the flag set from SSA; this should no longer be necessary.

src/coreclr/jit/compiler.h

@@ -530,10 +530,9 @@ class LclVarDsc
                                   // 32-bit target.  For implicit byref parameters, this gets hijacked between
                                   // fgRetypeImplicitByRefArgs and fgMarkDemotedImplicitByRefArgs to indicate whether
                                   // references to the arg are being rewritten as references to a promoted shadow local.
-    unsigned char lvIsStructField : 1;     // Is this local var a field of a promoted struct local?
-    unsigned char lvOverlappingFields : 1; // True when we have a struct with possibly overlapping fields
-    unsigned char lvContainsHoles : 1;     // True when we have a promoted struct that contains holes
-    unsigned char lvCustomLayout : 1;      // True when this struct has "CustomLayout"
+    unsigned char lvIsStructField : 1; // Is this local var a field of a promoted struct local?
+    unsigned char lvContainsHoles : 1; // True when we have a promoted struct that contains holes
+    unsigned char lvCustomLayout : 1;  // True when this struct has "CustomLayout"
 
     unsigned char lvIsMultiRegArg : 1; // true if this is a multireg LclVar struct used in an argument context
     unsigned char lvIsMultiRegRet : 1; // true if this is a multireg LclVar struct assigned from a multireg call

src/coreclr/jit/lclvars.cpp

@@ -1482,11 +1482,6 @@ void Compiler::lvaInitVarDsc(LclVarDsc*              varDsc,
         compFloatingPointUsed = true;
     }
 
-    if (typeHnd != NO_CLASS_HANDLE)
-    {
-        varDsc->lvOverlappingFields = StructHasOverlappingFields(info.compCompHnd->getClassAttribs(typeHnd));
-    }
-
 #if FEATURE_IMPLICIT_BYREFS
     varDsc->lvIsImplicitByRef = 0;
 #endif // FEATURE_IMPLICIT_BYREFS
@@ -3074,8 +3069,6 @@ void Compiler::lvaSetStruct(unsigned varNum, CORINFO_CLASS_HANDLE typeHnd, bool
 
     unsigned classAttribs = info.compCompHnd->getClassAttribs(typeHnd);
 
-    varDsc->lvOverlappingFields = StructHasOverlappingFields(classAttribs);
-
     // Check whether this local is an unsafe value type and requires GS cookie protection.
     // GS checks require the stack to be re-ordered, which can't be done with EnC.
     if (unsafeValueClsCheck && (classAttribs & CORINFO_FLG_UNSAFE_VALUECLASS) && !opts.compDbgEnC)
@@ -7930,10 +7923,6 @@ void Compiler::lvaDumpEntry(unsigned lclNum, FrameLayoutState curState, size_t r
     if (varDsc->lvStructDoubleAlign)
         printf(" double-align");
 #endif // !TARGET_64BIT
-    if (varDsc->lvOverlappingFields)
-    {
-        printf(" overlapping-fields");
-    }
 
     if (compGSReorderStackLayout && !varDsc->lvRegister)
     {

src/coreclr/jit/morph.cpp

@@ -16627,12 +16627,6 @@ PhaseStatus Compiler::fgRetypeImplicitByRefArgs()
             // Since the parameter in this position is really a pointer, its type is TYP_BYREF.
             varDsc->lvType = TYP_BYREF;
 
-            // Since this previously was a TYP_STRUCT and we have changed it to a TYP_BYREF
-            // make sure that the following flag is not set as these will force SSA to
-            // exclude tracking/enregistering these LclVars. (see SsaBuilder::IncludeInSsa)
-            //
-            varDsc->lvOverlappingFields = 0; // This flag could have been set, clear it.
-
             // The struct parameter may have had its address taken, but the pointer parameter
             // cannot -- any uses of the struct parameter's address are uses of the pointer
             // parameter's value, and there's no way for the MSIL to reference the pointer

src/coreclr/jit/ssabuilder.cpp

@@ -1644,11 +1644,6 @@ bool SsaBuilder::IncludeInSsa(unsigned lclNum)
     // lvPromoted structs are never tracked...
     assert(!varDsc->lvPromoted);
 
-    if (varDsc->lvOverlappingFields)
-    {
-        return false; // Don't use SSA on structs that have overlapping fields
-    }
-
     if (varDsc->lvIsStructField &&
         (m_pCompiler->lvaGetParentPromotionType(lclNum) != Compiler::PROMOTION_TYPE_INDEPENDENT))
     {