Don't check handles in substitution (#76730)

* Remove the struct handle check in substitution

* Fix an assert

src/coreclr/jit/forwardsub.cpp

@@ -660,33 +660,6 @@ bool Compiler::fgForwardSubStatement(Statement* stmt)
         return false;
     }
 
-    // We may sometimes lose or change a type handle. Avoid substituting if so.
-    //
-    // However, we allow free substitution of hardware SIMD types.
-    //
-    CORINFO_CLASS_HANDLE fwdHnd = gtGetStructHandleIfPresent(fwdSubNode);
-    CORINFO_CLASS_HANDLE useHnd = gtGetStructHandleIfPresent(fsv.GetNode());
-    if (fwdHnd != useHnd)
-    {
-        if ((fwdHnd == NO_CLASS_HANDLE) || (useHnd == NO_CLASS_HANDLE))
-        {
-            JITDUMP(" would add/remove struct handle (substitution)\n");
-            return false;
-        }
-
-#ifdef FEATURE_SIMD
-        const bool bothHWSIMD = isHWSIMDClass(fwdHnd) && isHWSIMDClass(useHnd);
-#else
-        const bool bothHWSIMD = false;
-#endif
-
-        if (!bothHWSIMD)
-        {
-            JITDUMP(" would change struct handle (substitution)\n");
-            return false;
-        }
-    }
-
     // There are implicit assumptions downstream on where/how multi-reg ops
     // can appear.
     //

src/coreclr/jit/gentree.cpp

@@ -15423,12 +15423,11 @@ GenTree* Compiler::gtNewTempAssign(
     CORINFO_CLASS_HANDLE valStructHnd = gtGetStructHandleIfPresent(val);
     if (varTypeIsStruct(varDsc) && (valStructHnd == NO_CLASS_HANDLE) && !varTypeIsSIMD(valTyp))
     {
-        // There are 2 special cases:
-        // 1. we have lost classHandle from a FIELD node  because the parent struct has overlapping fields,
-        //     the field was transformed as IND opr GT_LCL_FLD;
-        // 2. we are propagation `ASG(struct V01, 0)` to `RETURN(struct V01)`, `CNT_INT` doesn't `structHnd`;
-        // in these cases, we can use the type of the merge return for the assignment.
-        assert(val->gtEffectiveVal(true)->OperIs(GT_IND, GT_LCL_FLD, GT_CNS_INT));
+        // There are some cases where we do not have a struct handle on the return value:
+        // 1. Handle-less IND/BLK/LCL_FLD<struct> nodes.
+        // 2. The zero constant created by local assertion propagation.
+        // In these cases, we can use the type of the merge return for the assignment.
+        assert(val->gtEffectiveVal(true)->OperIs(GT_IND, GT_BLK, GT_LCL_FLD, GT_CNS_INT));
         assert(tmp == genReturnLocal);
         valStructHnd = lvaGetStruct(genReturnLocal);
         assert(valStructHnd != NO_CLASS_HANDLE);

src/coreclr/jit/importer.cpp

@@ -1042,7 +1042,7 @@ GenTree* Compiler::impAssignStructPtr(GenTree*             destAddr,
     else
 #endif // FEATURE_HW_INTRINSICS
     {
-        assert(src->OperIs(GT_LCL_VAR, GT_LCL_FLD, GT_FIELD, GT_IND, GT_OBJ, GT_CALL, GT_MKREFANY, GT_RET_EXPR,
+        assert(src->OperIs(GT_LCL_VAR, GT_LCL_FLD, GT_FIELD, GT_IND, GT_OBJ, GT_BLK, GT_CALL, GT_MKREFANY, GT_RET_EXPR,
                            GT_COMMA, GT_CNS_VEC) ||
                ((src->TypeGet() != TYP_STRUCT) && (src->OperIsSIMD() || src->OperIs(GT_BITCAST))));
     }

src/coreclr/jit/lower.cpp

@@ -3719,6 +3719,7 @@ void Lowering::LowerRetStruct(GenTreeUnOp* ret)
             }
             break;
 
+        case GT_BLK:
         case GT_OBJ:
             retVal->ChangeOper(GT_IND);
             FALLTHROUGH;