8010437: guarantee(this->is8bit(imm8)) failed: Short forward jump exceeds 8-bit offset Summary: Fix shorten_branches() to accurately count an initial nop that may be inserted in a block that starts with a safepoint. Reviewed-by: kvn

8011102: Clear AVX registers after return from JNI call Summary: Execute vzeroupper instruction after JNI call and on exits in jit compiled code which use 256bit vectors. Reviewed-by: roland