Enable multireg returns on Arm64

Added method IsMultiRegPassedType and updated IsMultiRegReturnType
Switched these methods to using getArgTypeForStruct and getReturnTypeForStruct
Removed IsRegisterPassable and used IsMultiRegReturned instead.
Converted lvIsMultiregStruct to use getArgTypeForStruct
Renamed varDsc->lvIsMultiregStruct() to compiler->lvaIsMultiregStruct(varDsc)
Skip calling getPrimitiveTypeForStruct when we have a struct larger than 8 bytes
Refactored ReturnTypeDesc::InitializeReturnType
Fixed missing SPK_ByReference case in InitializeReturnType
Fixes for RyiJIt x86 TYP_LONG return types and additional ARM64 work for full multireg support
Added ARM64 guard the uses of MAX_RET_MULTIREG_BYTES with FEATURE_MULTIREG_RET
Fixes for multireg returns in Arm64 Codegen
Added dumping of lvIsMultiRegArg and lvIsMultiRegRet in the assembly output
Added check and set of compFloatingPointUsed to InitializeStructReturnType
Fixes to handle JIT helper calls that say they return a TYP_STRUCT with no class handle available
Placed all of the second GC return reg under MULTIREG_HAS_SECOND_GC_RET ifdefs
Added the Arm64 VM changes from Rahul's PR 5175
Update getArgTypeForStruct for x86/arm32 so that it returns TYP_STRUCT for all pass by value cases
Fixes for the passing of 3,5,6 or 7 byte sized structs
Fix issue on ARM64 where we would back fill into x7 after passing a 16-byte struct on the stack
Implemented register shuffling for multi reg Call returns on Arm64
Fixed regression on Arm32 for struct args that are not multi regs
Updated Tests.Lst with 23 additional passing tests

Changes from codereview feedback

1 files changed, 4 insertions, 6 deletions

diff --git a/src/jit/emit.h b/src/jit/emit.h
index c8de077dc1..e3eee557d4 100644
--- a/src/jit/emit.h
+++ b/src/jit/emit.h
@@ -1241,14 +1241,12 @@ protected:
         regMaskTP       idcByrefRegs;              // ... byref registers
         unsigned        idcArgCnt;                 // ... lots of args or (<0 ==> caller pops args)
 
-#ifdef FEATURE_UNIX_AMD64_STRUCT_PASSING
+#if MULTIREG_HAS_SECOND_GC_RET
         // This method handle the GC-ness of the second register in a 2 register returned struct on System V.
         GCtype          idSecondGCref() const { return (GCtype)_idcSecondRetRegGCType; }
         void            idSecondGCref(GCtype gctype) { _idcSecondRetRegGCType = gctype; }
-#endif // FEATURE_UNIX_AMD64_STRUCT_PASSING
 
     private:
-#ifdef FEATURE_UNIX_AMD64_STRUCT_PASSING
         // This member stores the GC-ness of the second register in a 2 register returned struct on System V.
         // It is added to the call struct since it is not needed by the base instrDesc struct, which keeps GC-ness
         // of the first register for the instCall nodes.
@@ -1257,7 +1255,7 @@ protected:
         // since the GC-ness of the second register is only needed for call instructions.
         // The base struct's member keeping the GC-ness of the first return register is _idGCref.
         GCtype          _idcSecondRetRegGCType : 2;      // ... GC type for the second return register.  
-#endif // FEATURE_UNIX_AMD64_STRUCT_PASSING  
+#endif // MULTIREG_HAS_SECOND_GC_RET
     };
 
     struct          instrDescArmFP : instrDesc  
@@ -1640,9 +1638,9 @@ private:
 
     regNumber       emitSyncThisObjReg; // where is "this" enregistered for synchronized methods?
 
-#ifdef FEATURE_UNIX_AMD64_STRUCT_PASSING
+#if MULTIREG_HAS_SECOND_GC_RET
     void            emitSetSecondRetRegGCType(instrDescCGCA* id, emitAttr secondRetSize); 
-#endif // FEATURE_UNIX_AMD64_STRUCT_PASSING
+#endif // MULTIREG_HAS_SECOND_GC_RET
 
     static void     emitEncodeCallGCregs(regMaskTP regs, instrDesc *id);
     static unsigned emitDecodeCallGCregs(instrDesc *id);