Revert "Skip unprofitable cases"

This reverts commit 112370f.

Author: jakobbotsch

src/coreclr/jit/lower.cpp

@@ -5059,7 +5059,7 @@ bool Lowering::IsFieldListCompatibleWithReturn(GenTreeFieldList* fieldList)
         }
 
         var_types fieldType = genActualType(use.GetNode());
-        var_types regType   = genActualType(retDesc.GetReturnRegType(regIndex));
+        var_types regType   = retDesc.GetReturnRegType(regIndex);
         if (genTypeSize(fieldType) != genTypeSize(regType))
         {
             JITDUMP("it is not; field %u register has type %s but field has type %s\n", regIndex, varTypeName(regType),

src/coreclr/jit/promotion.cpp

@@ -2306,11 +2306,6 @@ bool ReplaceVisitor::ReplaceReturnedStructLocal(GenTreeOp* ret, GenTreeLclVarCom
         return false;
     }
 
-    if (!IsReturnProfitableAsFieldList(value))
-    {
-        return false;
-    }
-
     StructDeaths      deaths    = m_liveness->GetDeathsForStructLocal(value);
     GenTreeFieldList* fieldList = m_compiler->gtNewFieldList();
 
@@ -2348,49 +2343,6 @@ bool ReplaceVisitor::ReplaceReturnedStructLocal(GenTreeOp* ret, GenTreeLclVarCom
     return true;
 }
 
-//------------------------------------------------------------------------
-// IsReturnProfitableAsFieldList:
-//   Check if a returned local is expected to be profitable to turn into a
-//   FIELD_LIST.
-//
-// Parameters:
-//   value - The struct local
-//
-// Returns:
-//   True if so.
-//
-bool ReplaceVisitor::IsReturnProfitableAsFieldList(GenTreeLclVarCommon* value)
-{
-    // Currently the backend requires all fields to map cleanly to registers to
-    // efficiently return them. Otherwise they will be spilled, and we are
-    // better off decomposing the store here.
-    auto fieldMapsCleanly = [=](Replacement& rep) {
-        const ReturnTypeDesc& retDesc     = m_compiler->compRetTypeDesc;
-        unsigned              fieldOffset = rep.Offset - value->GetLclOffs();
-        unsigned              numRegs     = retDesc.GetReturnRegCount();
-        for (unsigned i = 0; i < numRegs; i++)
-        {
-            unsigned  offset  = retDesc.GetReturnFieldOffset(i);
-            var_types regType = retDesc.GetReturnRegType(i);
-            if ((fieldOffset == offset) && (genTypeSize(rep.AccessType) == genTypeSize(regType)))
-            {
-                return true;
-            }
-        }
-
-        return false;
-    };
-
-    unsigned size = value->GetLayout(m_compiler)->GetSize();
-    if (!VisitOverlappingReplacements(value->GetLclNum(), value->GetLclOffs(), size, fieldMapsCleanly))
-    {
-        // Aborted early, so a field did not map
-        return false;
-    }
-
-    return true;
-}
-
 //------------------------------------------------------------------------
 // ReplaceCallArgWithFieldList:
 //   Handle a call that may pass a struct local with replacements as the

src/coreclr/jit/promotion.h

@@ -296,7 +296,6 @@ class ReplaceVisitor : public GenTreeVisitor<ReplaceVisitor>
 
     bool ReplaceStructLocal(GenTree* user, GenTreeLclVarCommon* value);
     bool ReplaceReturnedStructLocal(GenTreeOp* ret, GenTreeLclVarCommon* value);
-    bool IsReturnProfitableAsFieldList(GenTreeLclVarCommon* value);
     bool ReplaceCallArgWithFieldList(GenTreeCall* call, GenTreeLclVarCommon* callArg);
     bool CanReplaceCallArgWithFieldListOfReplacements(GenTreeCall* call, CallArg* callArg, GenTreeLclVarCommon* lcl);
     void ReadBackAfterCall(GenTreeCall* call, GenTree* user);