ImplicitNullChecks did not work on platforms where the zero page is only write protected. This change adds os property 'zero_page_read_protected' and extends the ImplicitNullCheck optimization to consider only stores if this property is not true. If a decoded compressed oop will access the guard page before the heap, Loads work again. This is needed on AIX, where the page at address '0' is only write-protected. ---------------------------- This is preparation for PPC64 integration: http://openjdk.java.net/jeps/175 This and following ppc64 changes will go into staging repository first and tested there: http://hg.openjdk.java.net/ppc-aix-port/stage/ http://hg.openjdk.java.net/ppc-aix-port/jdk8/hotspot/file/338e318f1e12/ppc_patches/0215_opto-extend_ImplicitNullCheck_optimizations.patch