[Arm64] Fix genCodeForCpObj()

CORINFO_HELP_ASSIGN_BYREF is the functional equivalent to

   *dst = *src;
   ++dst;
   ++src;

Note: Description ignores barriers.

Since src and dst are incremented the registers are marked dead.

In genCodeForCpObj(), the incremented values are will be reused
and therefore must be treated as live.  Add code to explicitly
force them live for this use case.

Commit migrated from https://github.com/dotnet/coreclr/commit/a5d464837248bae64845fb3e8207821d29f316d8

diff --git a/src/coreclr/src/jit/codegenarm64.cpp b/src/coreclr/src/jit/codegenarm64.cpp
index 48d6f76..7cc9622 100644 (file)
--- a/src/coreclr/src/jit/codegenarm64.cpp
+++ b/src/coreclr/src/jit/codegenarm64.cpp
@@ -3626,8 +3626,14 @@ void CodeGen::genCodeForCpObj(GenTreeObj* cpObjNode)
                     break;
 
                 default:
-                    // We have a GC pointer, call the memory barrier.
+                    // In the case of a GC-Pointer we'll call the ByRef write barrier helper
                     genEmitHelperCall(CORINFO_HELP_ASSIGN_BYREF, 0, EA_PTRSIZE);
+
+                    // genEmitHelperCall(CORINFO_HELP_ASSIGN_BYREF...) killed these registers.
+                    // However they are still live references to the structures we are copying.
+                    gcInfo.gcMarkRegPtrVal(REG_WRITE_BARRIER_SRC_BYREF, TYP_BYREF);
+                    gcInfo.gcMarkRegPtrVal(REG_WRITE_BARRIER_DST_BYREF, TYP_BYREF);
+
                     gcPtrCount--;
                     break;
             }