JIT: Reimport full spill clique for I_IMPL<->BYREF mismatches

src/coreclr/jit/importer.cpp

@@ -11387,19 +11387,17 @@ void Compiler::impImportBlock(BasicBlock* block)
         {
             GenTree* tree = verCurrentState.esStack[level].val;
 
-            /* VC generates code where it pushes a byref from one branch, and an int (ldc.i4 0) from
-               the other. This should merge to a byref in unverifiable code.
-               However, if the branch which leaves the TYP_I_IMPL on the stack is imported first, the
-               successor would be imported assuming there was a TYP_I_IMPL on
-               the stack. Thus the value would not get GC-tracked. Hence,
-               change the temp to TYP_BYREF and reimport the successors.
-               Note: We should only allow this in unverifiable code.
-            */
+            // VC generates code where it pushes a byref from one branch, and an int (ldc.i4 0) from
+            // the other. This should merge to a byref in unverifiable code.
+            // However, if the branch which leaves the TYP_I_IMPL on the stack is imported first, the
+            // successor would be imported assuming there was a TYP_I_IMPL on
+            // the stack. Thus the value would not get GC-tracked. Hence,
+            // change the temp to TYP_BYREF and reimport the clique.
+            // Note: We should only allow this in unverifiable code.
             if (tree->gtType == TYP_BYREF && lvaTable[tempNum].lvType == TYP_I_IMPL)
             {
                 lvaTable[tempNum].lvType = TYP_BYREF;
-                impReimportMarkSuccessors(block);
-                markImport = true;
+                reimportSpillClique      = true;
             }
 
 #ifdef TARGET_64BIT

src/coreclr/jit/lclvars.cpp

@@ -4146,7 +4146,6 @@ void Compiler::lvaMarkLclRefs(GenTree* tree, BasicBlock* block, Statement* stmt,
 
         // Check that the LCL_VAR node has the same type as the underlying variable, save a few mismatches we allow.
         assert(tree->TypeIs(varDsc->TypeGet(), genActualType(varDsc)) ||
-               (tree->TypeIs(TYP_I_IMPL) && (varDsc->TypeGet() == TYP_BYREF)) || // Created for spill clique import.
                (tree->TypeIs(TYP_BYREF) && (varDsc->TypeGet() == TYP_I_IMPL)) || // Created by inliner substitution.
                (tree->TypeIs(TYP_INT) && (varDsc->TypeGet() == TYP_LONG)));      // Created by "optNarrowTree".
     }

src/coreclr/jit/morphblock.cpp

@@ -1183,8 +1183,7 @@ GenTree* MorphCopyBlockHelper::CopyFieldByField()
         addrSpillTemp = m_comp->lvaGrabTemp(true DEBUGARG("BlockOp address local"));
 
         LclVarDsc* addrSpillDsc = m_comp->lvaGetDesc(addrSpillTemp);
-        addrSpillDsc->lvType = addrSpill->TypeIs(TYP_REF) ? TYP_REF : TYP_BYREF; // TODO-ASG: zero-diff quirk, delete.
-        addrSpillStore       = m_comp->gtNewTempStore(addrSpillTemp, addrSpill);
+        addrSpillStore          = m_comp->gtNewTempStore(addrSpillTemp, addrSpill);
     }
 
     auto grabAddr = [=, &result](unsigned offs) {
@@ -1227,7 +1226,12 @@ GenTree* MorphCopyBlockHelper::CopyFieldByField()
             // handling.
             GenTreeIntCon* fldOffsetNode = m_comp->gtNewIconNode(fullOffs, TYP_I_IMPL);
             fldOffsetNode->gtFieldSeq    = addrBaseOffsFldSeq;
-            addrClone                    = m_comp->gtNewOperNode(GT_ADD, TYP_BYREF, addrClone, fldOffsetNode);
+            addrClone = m_comp->gtNewOperNode(GT_ADD, varTypeIsGC(addrClone) ? TYP_BYREF : TYP_I_IMPL, addrClone,
+                                              fldOffsetNode);
+            // Avoid constant prop propagating each field access with a large
+            // constant address. TODO-Cleanup: We should tune constant prop to
+            // have better heuristics around this.
+            addrClone->gtFlags |= GTF_DONT_CSE;
         }
 
         return addrClone;