7143491: G1 C2 CTW: assert(p2x->outcnt() == 2) failed: expects 2 users: Xor and URShift nodes Summary: Adjust the assert and code in eliminate_card_mark() method for case when stored value is NULL. Reviewed-by: iveresov, never

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; This .DEF file is a placeholder for one which is automatically
; generated during the build process. See
; make\windows\build_vm_def.sh and
; make\windows\makefiles\projectcreator.make (esp. the "-prelink"
; options).
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