Rework JIT<->EE communication for struct promotion; add support for general recursive struct promotion

src/coreclr/inc/corinfo.h

@@ -857,10 +857,8 @@ enum CorInfoFlag
     CORINFO_FLG_OVERLAPPING_FIELDS    = 0x00100000, // struct or class has fields that overlap (aka union)
     CORINFO_FLG_INTERFACE             = 0x00200000, // it is an interface
     CORINFO_FLG_DONT_DIG_FIELDS       = 0x00400000, // don't ask field info (used for types outside of AOT compilation version bubble)
-    CORINFO_FLG_CUSTOMLAYOUT          = 0x00800000, // does this struct have custom layout?
     CORINFO_FLG_CONTAINS_GC_PTR       = 0x01000000, // does the class contain a gc ptr ?
     CORINFO_FLG_DELEGATE              = 0x02000000, // is this a subclass of delegate or multicast delegate ?
-    CORINFO_FLG_INDEXABLE_FIELDS      = 0x04000000, // struct fields may be accessed via indexing (used for inline arrays)
     CORINFO_FLG_BYREF_LIKE            = 0x08000000, // it is byref-like value type
     CORINFO_FLG_VARIANCE              = 0x10000000, // MethodTable::HasVariance (sealed does *not* mean uncast-able)
     CORINFO_FLG_BEFOREFIELDINIT       = 0x20000000, // Additional flexibility for when to run .cctor (see code:#ClassConstructionFlags)
@@ -1946,6 +1944,25 @@ struct CORINFO_VarArgInfo
                                             // (The CORINFO_VARARGS_HANDLE counts as an arg)
 };
 
+struct CORINFO_FLATTENED_TYPE_FIELD
+{
+    // Primitive type, or CORINFO_TYPE_VALUECLASS for value classes marked as intrinsic.
+    CorInfoType type;
+    // For an intrinsic value class this is the handle for it.
+    CORINFO_CLASS_HANDLE intrinsicValueClassHnd;
+    // Offset of the field into the root struct.
+    unsigned offset;
+    // Field handle (only used for diagnostic purposes)
+    CORINFO_FIELD_HANDLE fieldHandle;
+};
+
+enum class FlattenTypeResult
+{
+    Success,
+    Partial,
+    Failure,
+};
+
 #define SIZEOF__CORINFO_Object                            TARGET_POINTER_SIZE /* methTable */
 
 #define CORINFO_Array_MaxLength                           0x7FFFFFC7
@@ -2448,6 +2465,29 @@ class ICorStaticInfo
             int32_t num
             ) = 0;
 
+    //------------------------------------------------------------------------------
+    // flattenType: Flatten a type into its primitive/intrinsic constituent
+    // fields.
+    //
+    // Parameters:
+    //    clsHnd             - Handle of the type.
+    //    fields             - [out] Pointer to entries to write.
+    //    numFields          - [in, out] Size of 'fields'. Updated to contain
+    //                         the number of entries written in 'fields'.
+    //    significantPadding - [out] Whether data not covered by fields should
+    //                         be considered as significant or whether the JIT
+    //                         is allowed to discard it on copies.
+    //
+    // Returns:
+    //    A result indicating whether the type was successfully flattened and
+    //    whether the result is partial or not.
+    //
+    virtual FlattenTypeResult flattenType(
+            CORINFO_CLASS_HANDLE clsHnd,
+            CORINFO_FLATTENED_TYPE_FIELD* fields,
+            size_t* numFields,
+            bool* significantPadding) = 0;
+
     virtual bool checkMethodModifier(
             CORINFO_METHOD_HANDLE hMethod,
             const char * modifier,

src/coreclr/inc/icorjitinfoimpl_generated.h

@@ -263,6 +263,12 @@ CORINFO_FIELD_HANDLE getFieldInClass(
           CORINFO_CLASS_HANDLE clsHnd,
           int32_t num) override;
 
+FlattenTypeResult flattenType(
+          CORINFO_CLASS_HANDLE clsHnd,
+          CORINFO_FLATTENED_TYPE_FIELD* fields,
+          size_t* numFields,
+          bool* significantPadding) override;
+
 bool checkMethodModifier(
           CORINFO_METHOD_HANDLE hMethod,
           const char* modifier,

src/coreclr/inc/jiteeversionguid.h

@@ -43,11 +43,11 @@ typedef const GUID *LPCGUID;
 #define GUID_DEFINED
 #endif // !GUID_DEFINED
 
-constexpr GUID JITEEVersionIdentifier = { /* 4e6355a0-3844-45e2-8cef-082c18217e14 */
-    0x4e6355a0,
-    0x3844,
-    0x45e2,
-    {0x8c, 0xef, 0x8, 0x2c, 0x18, 0x21, 0x7e, 0x14}
+constexpr GUID JITEEVersionIdentifier = { /* 878d63a7-ffc9-421f-81f7-db4729f0ed5c */
+    0x878d63a7,
+    0xffc9,
+    0x421f,
+    {0x81, 0xf7, 0xdb, 0x47, 0x29, 0xf0, 0xed, 0x5c}
   };
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////////

src/coreclr/jit/ICorJitInfo_names_generated.h

@@ -64,6 +64,7 @@ DEF_CLR_API(getClassAlignmentRequirement)
 DEF_CLR_API(getClassGClayout)
 DEF_CLR_API(getClassNumInstanceFields)
 DEF_CLR_API(getFieldInClass)
+DEF_CLR_API(flattenType)
 DEF_CLR_API(checkMethodModifier)
 DEF_CLR_API(getNewHelper)
 DEF_CLR_API(getNewArrHelper)

src/coreclr/jit/ICorJitInfo_wrapper_generated.hpp

@@ -599,6 +599,18 @@ CORINFO_FIELD_HANDLE WrapICorJitInfo::getFieldInClass(
     return temp;
 }
 
+FlattenTypeResult WrapICorJitInfo::flattenType(
+          CORINFO_CLASS_HANDLE clsHnd,
+          CORINFO_FLATTENED_TYPE_FIELD* fields,
+          size_t* numFields,
+          bool* significantPadding)
+{
+    API_ENTER(flattenType);
+    FlattenTypeResult temp = wrapHnd->flattenType(clsHnd, fields, numFields, significantPadding);
+    API_LEAVE(flattenType);
+    return temp;
+}
+
 bool WrapICorJitInfo::checkMethodModifier(
           CORINFO_METHOD_HANDLE hMethod,
           const char* modifier,

src/coreclr/jit/compiler.h

@@ -593,8 +593,13 @@ class LclVarDsc
                                   // 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 lvContainsHoles : 1; // True when we have a promoted struct that contains holes
-    unsigned char lvCustomLayout : 1;  // True when this struct has "CustomLayout"
+    unsigned char lvContainsHoles : 1; // Is this a promoted struct whose fields do not cover the struct local?
+
+    // True for a promoted struct that has significant padding in it.
+    // Significant padding is any data in the struct that is not covered by a
+    // promoted field and that the EE told us we need to preserve on block
+    // copies/inits.
+    unsigned char lvAnySignificantPadding : 1;
 
     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
@@ -3561,8 +3566,8 @@ class Compiler
     struct lvaStructFieldInfo
     {
         CORINFO_FIELD_HANDLE fldHnd;
-        unsigned char        fldOffset;
-        unsigned char        fldOrdinal;
+        uint8_t              fldOffset;
+        uint8_t              fldOrdinal;
         var_types            fldType;
         unsigned             fldSize;
         CORINFO_CLASS_HANDLE fldTypeHnd;
@@ -3579,27 +3584,20 @@ class Compiler
         CORINFO_CLASS_HANDLE typeHnd;
         bool                 canPromote;
         bool                 containsHoles;
-        bool                 customLayout;
-        bool                 fieldsSorted;
+        bool                 anySignificantPadding;
         unsigned char        fieldCnt;
         lvaStructFieldInfo   fields[MAX_NumOfFieldsInPromotableStruct];
 
         lvaStructPromotionInfo(CORINFO_CLASS_HANDLE typeHnd = nullptr)
             : typeHnd(typeHnd)
             , canPromote(false)
             , containsHoles(false)
-            , customLayout(false)
-            , fieldsSorted(false)
+            , anySignificantPadding(false)
             , fieldCnt(0)
         {
         }
     };
 
-    struct lvaFieldOffsetCmp
-    {
-        bool operator()(const lvaStructFieldInfo& field1, const lvaStructFieldInfo& field2);
-    };
-
     // This class is responsible for checking validity and profitability of struct promotion.
     // If it is both legal and profitable, then TryPromoteStructVar promotes the struct and initializes
     // necessary information for fgMorphStructField to use.
@@ -3619,12 +3617,7 @@ class Compiler
         bool CanPromoteStructVar(unsigned lclNum);
         bool ShouldPromoteStructVar(unsigned lclNum);
         void PromoteStructVar(unsigned lclNum);
-        void SortStructFields();
-
-        bool CanConstructAndPromoteField(lvaStructPromotionInfo* structPromotionInfo);
-
-        lvaStructFieldInfo GetFieldInfo(CORINFO_FIELD_HANDLE fieldHnd, BYTE ordinal);
-        bool TryPromoteStructField(lvaStructFieldInfo& outerFieldInfo);
+        var_types TryPromoteIntrinsicTypeAsPrimitive(CORINFO_CLASS_HANDLE clsHnd);
 
     private:
         Compiler*              compiler;
@@ -8610,14 +8603,19 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         return pTypeInfo->IsStruct() && isSIMDClass(pTypeInfo->GetClassHandleForValueClass());
     }
 
+    bool isRuntimeIntrinsicsNamespace(const char* ns)
+    {
+        return strcmp(ns, "System.Runtime.Intrinsics") == 0;
+    }
+
     bool isHWSIMDClass(CORINFO_CLASS_HANDLE clsHnd)
     {
 #ifdef FEATURE_HW_INTRINSICS
         if (isIntrinsicType(clsHnd))
         {
             const char* namespaceName = nullptr;
             (void)getClassNameFromMetadata(clsHnd, &namespaceName);
-            return strcmp(namespaceName, "System.Runtime.Intrinsics") == 0;
+            return isRuntimeIntrinsicsNamespace(namespaceName);
         }
 #endif // FEATURE_HW_INTRINSICS
         return false;

src/coreclr/jit/compiler.hpp

@@ -4276,21 +4276,11 @@ inline static bool StructHasOverlappingFields(DWORD attribs)
     return ((attribs & CORINFO_FLG_OVERLAPPING_FIELDS) != 0);
 }
 
-inline static bool StructHasCustomLayout(DWORD attribs)
-{
-    return ((attribs & CORINFO_FLG_CUSTOMLAYOUT) != 0);
-}
-
 inline static bool StructHasDontDigFieldsFlagSet(DWORD attribs)
 {
     return ((attribs & CORINFO_FLG_DONT_DIG_FIELDS) != 0);
 }
 
-inline static bool StructHasIndexableFields(DWORD attribs)
-{
-    return ((attribs & CORINFO_FLG_INDEXABLE_FIELDS) != 0);
-}
-
 //------------------------------------------------------------------------------
 // DEBUG_DESTROY_NODE: sets value of tree to garbage to catch extra references
 //

src/coreclr/jit/forwardsub.cpp

@@ -584,7 +584,8 @@ bool Compiler::fgForwardSubStatement(Statement* stmt)
     bool found = false;
     for (GenTreeLclVarCommon* lcl : nextStmt->LocalsTreeList())
     {
-        if (lcl->OperIs(GT_LCL_VAR) && (lcl->GetLclNum() == lclNum))
+        bool isUse = ((lcl->gtFlags) & GTF_VAR_DEF) == 0;
+        if (lcl->OperIs(GT_LCL_VAR) && (lcl->GetLclNum() == lclNum) && isUse)
         {
             if (fsv.IsLastUse(lcl->AsLclVar()))
             {

src/coreclr/jit/gentree.cpp

@@ -11961,28 +11961,13 @@ void Compiler::gtDispLeaf(GenTree* tree, IndentStack* indentStack)
                 {
                     for (unsigned index = 0; index < varDsc->lvFieldCnt; index++)
                     {
-                        unsigned    fieldLclNum = varDsc->lvFieldLclStart + index;
-                        LclVarDsc*  fieldVarDsc = lvaGetDesc(fieldLclNum);
-                        const char* fieldName;
-#if !defined(TARGET_64BIT)
-                        if (varTypeIsLong(varDsc))
-                        {
-                            fieldName = (index == 0) ? "lo" : "hi";
-                        }
-                        else
-#endif // !defined(TARGET_64BIT)
-                        {
-                            CORINFO_CLASS_HANDLE typeHnd = varDsc->GetLayout()->GetClassHandle();
-                            CORINFO_FIELD_HANDLE fldHnd =
-                                info.compCompHnd->getFieldInClass(typeHnd, fieldVarDsc->lvFldOrdinal);
-                            fieldName = eeGetFieldName(fldHnd, true, buffer, sizeof(buffer));
-                        }
+                        unsigned   fieldLclNum = varDsc->lvFieldLclStart + index;
+                        LclVarDsc* fieldVarDsc = lvaGetDesc(fieldLclNum);
 
                         printf("\n");
                         printf("                                                            ");
                         printIndent(indentStack);
-                        printf("    %-6s V%02u.%s (offs=0x%02x) -> ", varTypeName(fieldVarDsc->TypeGet()),
-                               tree->AsLclVarCommon()->GetLclNum(), fieldName, fieldVarDsc->lvFldOffset);
+                        printf("    %-6s %s -> ", varTypeName(fieldVarDsc->TypeGet()), fieldVarDsc->lvReason);
                         gtDispLclVar(fieldLclNum);
                         gtDispSsaName(fieldLclNum, tree->AsLclVarCommon()->GetSsaNum(this, index), isDef);