Debugging the architecture-dependent AD file

[Gustavo Serra Scalet]

Hi,

I'd like to know if there is any easier way to debug the architecture-dependent
AD file. I see that some compilers include a set of gdb-python scripts in order
to facilitate debugging.

On this example I wanted to closely check how loadB_indirect_Ex is behaving on
ppc. I could manage to debug the hotspot overall, but I'm confused about what is
happening when looking at the AD file:

~/hs-comp $ ./build/linux-ppc64le-normal-server-slowdebug/jdk/bin/javac pidigits.java
~/hs-comp $ gdb ./build/linux-ppc64le-normal-server-slowdebug/jdk/bin/java
GNU gdb (Ubuntu 7.9-1ubuntu1) 7.9
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This GDB was configured as "powerpc64le-linux-gnu".
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Type "apropos word" to search for commands related to "word"...
Reading symbols from java...done.
(gdb 64) handle SIGILL nostop noprint pass
Signal        Stop      Print   Pass to program Description
SIGILL        No        No      Yes             Illegal instruction
(gdb 64) handle SIGSEGV nostop noprint pass
Signal        Stop      Print   Pass to program Description
SIGSEGV       No        No      Yes             Segmentation fault
(gdb 64) b ppc.ad:5030
No source file named ppc.ad.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (ppc.ad:5030) pending.
(gdb 64) r -Xcomp -XX:-UseSIGTRAP pidigits 10
Starting program: /home/gut/hs-comp/java -Xcomp -XX:-UseSIGTRAP pidigits 10
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/powerpc64le-linux-gnu/libthread_db.so.1".
[New Thread 0x3fffb61df1a0 (LWP 17208)]
... (removed for readability purposes)
[New Thread 0x3fffb534f1a0 (LWP 17209)]
[Switching to Thread 0x3ffe7944f1a0 (LWP 17292)]

Breakpoint 1, State::_sub_Op_LoadB (this=0x3ffe68044950, n=0x3ffe34326930) at /home/gut/hs-comp/hotspot/src/cpu/ppc/vm/ppc.ad:5031
warning: Source file is more recent than executable.
5031      predicate(n->as_Load()->is_unordered() || followed_by_acquire(n));
(gdb 64) l
5026    %}
5027
5028    // Load Byte (8bit signed). LoadB = LoadUB + ConvUB2B.
5029    instruct loadB_indirect_Ex(iRegIdst dst, indirectMemory mem) %{
5030      match(Set dst (LoadB mem));
5031      predicate(n->as_Load()->is_unordered() || followed_by_acquire(n));
5032      ins_cost(MEMORY_REF_COST + DEFAULT_COST);
5033      expand %{
5034        iRegIdst tmp;
5035        loadUB_indirect(tmp, mem);
(gdb 64) n
7500    dfa_ppc.cpp: No such file or directory.
(gdb 64) dir build/linux-ppc64le-normal-server-slowdebug/hotspot/variant-server/gensrc/adfiles/
Source directories searched: /home/gut/hs-comp/build/linux-ppc64le-normal-server-slowdebug/hotspot/variant-server/gensrc/adfiles:$cdir:$cwd
(gdb 64) l
7495            DFA_PRODUCTION__SET_VALID(RARG3REGI, loadB_indirect_ac_Ex_rule, c+1)
7496          }
7497          if (STATE__NOT_YET_VALID(RARG4REGI) || _cost[RARG4REGI] > c+1) {
7498            DFA_PRODUCTION__SET_VALID(RARG4REGI, loadB_indirect_ac_Ex_rule, c+1)
7499          }
7500        }
7501        if( STATE__VALID_CHILD(_kids[0], INDIRECTMEMORY) &&
7502            (
7503    #line 5031 "/home/gut/hs-comp/hotspot/src/cpu/ppc/vm/ppc.ad"
7504    n->as_Load()->is_unordered() || followed_by_acquire(n)
(gdb 64) #WTH?!
(gdb 64) fin
Run till exit from #0  State::_sub_Op_LoadB (this=0x3ffe68044950, n=0x3ffe34326930) at dfa_ppc.cpp:7514
State::DFA (this=0x3ffe68044950, opcode=156, n=0x3ffe34326930) at dfa_ppc.cpp:11395
11395     case Op_LoadB: { _sub_Op_LoadB(n);
(gdb 64) n
11676     }
(gdb 64)
11677     return true;
(gdb 64)
Matcher::Label_Root (this=0x3ffe7944b5d8, n=0x3ffe34326930, svec=0x3ffe68044950, control=0x3ffe34326748, mem=0x1)
    at /home/gut/hs-comp/hotspot/src/share/vm/opto/matcher.cpp:1565
1565      for( x = 0; x < _LAST_MACH_OPER; x++ )


I see that the wiki page dedicated to this topic is unfortunately empty:
https://wiki.openjdk.java.net/display/HotSpot/UsingGDB

And I also didn't find any blog post about this (I'm considering doing one after
I figure this out).

Thanks in advance