[RFC] Introduce BreakAtCompileId

[Leslie Zhai]

Hi,

OptoBreakpoint is very useful for debugging C2 compiler when porting 
some cpu for jdk8u. It is able to `b breakpoint` for breaking at the 
prolog about for example Compile_id = 2. But when fixed several bugs for 
C2, it needs to press `c` times and times again for reaching the proper 
Compile_id.

I `grep` Opto related options.  But there is no such one to break at the 
precise Compile_id.  Please teach me if there was :)

So here comes BreakAtCompileId. It is able to break at the precise 
Compile_id which you want to debug.


gdb -ex=r --args $JAVA -Xcomp -XX:+PrintCompilation 
-XX:BreakAtCompileId=430  -version


(gdb) b breakpoint
Breakpoint 1 at 0x7ffff633b0d0: breakpoint. (133 locations)

    6333  433       3 java.util.ImmutableCollections$List12::get (35 
bytes)   made not entrant

Thread 2 "java" hit Breakpoint 1, 0x00007ffff711f410 in os::breakpoint() 
() at /home/zhaixiang/projects
452         if (pslash != NULL) {
(gdb) si
0x00007fffe01b46d1 in ?? ()
(gdb) x/22i $pc-44
    0x7fffe01b46a5:      shl    $0x3,%edx
    0x7fffe01b46a8:      movabs $0x800000000,%r11
    0x7fffe01b46b2:      add    %r11,%r10
    0x7fffe01b46b5:      cmp    %r10,%rax
    0x7fffe01b46b8:      jne    0x7fffd87cf920
    0x7fffe01b46be:      nop
    0x7fffe01b46bf:      nop
    0x7fffe01b46c0:      mov    %eax,-0x16000(%rsp)
    0x7fffe01b46c7:      push   %rbp
    0x7fffe01b46c8:      sub    $0x10,%rsp
    0x7fffe01b46cc:      callq  0x7ffff711f410 <_ZN2os10breakpointEv>
=> 0x7fffe01b46d1:      mov    0xc(%rsi),%r11d
    0x7fffe01b46d5:      mov    0x10(%rsi),%r10d
    0x7fffe01b46d9:      cmp    %r11d,%r10d
    0x7fffe01b46dc:      je     0x7fffe01b46f6
    0x7fffe01b46de:      mov    $0x1,%eax
    0x7fffe01b46e3:      add    $0x10,%rsp
    0x7fffe01b46e7:      pop    %rbp
    0x7fffe01b46e8:      cmp    0x128(%r15),%rsp
    0x7fffe01b46ef:      ja     0x7fffe01b46fa
    0x7fffe01b46f5:      retq
    0x7fffe01b46f6:      xor    %eax,%eax
(gdb) i r
rax            0x7fffe01b46c0      140736953272000
rbx            0x8004699e8         34364365288
rcx            0x1                 1
rdx            0x7fffc5068980      140736498928000
rsi            0x62a020b40         26474580800
rdi            0x1                 1
rbp            0x7ffff5a668d0      0x7ffff5a668d0
rsp            0x7ffff5a66290      0x7ffff5a66290
r8             0x80008eeb0         34360323760
r9             0x7ffb4cf60         34354810720
r10            0x800012488         34359813256
r11            0x800000000         34359738368
r12            0x0                 0
r13            0x7292dae5          1922226917
r14            0x62a020818         26474579992
r15            0x7ffff00271e0      140737220080096
rip            0x7fffe01b46d1      0x7fffe01b46d1
eflags         0x206               [ PF IF ]
cs             0x33                51
ss             0x2b                43
ds             0x0                 0
es             0x0                 0
fs             0x0                 0
gs             0x0                 0


Thanks,
Leslie Zhai