hg: jdk/sandbox: 8217909: Make unused r12 register (without compressed oops) available to regalloc in C2

[chris.hegarty at oracle.com]

Changeset: 48b50573dee4
Author:    rkennke
Date:      2019-02-20 13:01 +0100
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/48b50573dee4

8217909: Make unused r12 register (without compressed oops) available to regalloc in C2
Reviewed-by: adinn, dlong, neliasso

! src/hotspot/cpu/x86/c2_init_x86.cpp
! src/hotspot/cpu/x86/x86_64.ad
! src/hotspot/share/adlc/formsopt.hpp