target-i386: remove helper_lock()

It's been superseded by the atomic helpers.

The use of the atomic helpers provides a significant performance and scalability
improvement. Below is the result of running the atomic_add-test microbenchmark with:
$ x86_64-linux-user/qemu-x86_64 tests/atomic_add-bench -o 5000000 -r $r -n $n
, where $n is the number of threads and $r is the allowed range for the additions.

The scenarios measured are:
- atomic: implements x86' ADDL with the atomic_add helper (i.e. this patchset)
- cmpxchg: implement x86' ADDL with a TCG loop using the cmpxchg helper
- master: before this patchset

Results sorted in ascending range, i.e. descending degree of contention.
Y axis is Throughput in Mops/s. Tests are run on an AMD machine with 64
Opteron 6376 cores.

atomic_add-bench: 5000000 ops/thread, [0,1] range

25 ++---------+----------+---------+----------+----------+----------+---++
+ atomic +-E--+ + + + + + |
|cmpxchg +-H--+ |
20 +Emaster +-N--+ ++
|| |
|++ |
|| |
15 +++ ++
|N| |
|+| |
10 ++| ++
|+|+ |
| | -+E+------ +++ ---+E+------+E+------+E+-----+E+------+E|
|+E+E+- +++ +E+------+E+-- |
5 ++|+ ++
|+N+H+--- +++ |
++++N+--+H++----+++ + +++ --++H+------+H+------+H++----+H+---+--- |
0 ++---------+-----H----+---H-----+----------+----------+----------+---H+
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 5000000 ops/thread, [0,2] range

25 ++---------+----------+---------+----------+----------+----------+---++
++atomic +-E--+ + + + + + |
|cmpxchg +-H--+ |
20 ++master +-N--+ ++
|E| |
|++ |
||E |
15 ++| ++
|N|| |
|+|| ---+E+------+E+-----+E+------+E|
10 ++| | ---+E+------+E+-----+E+--- +++ +++
||H+E+--+E+-- |
|+++++ |
| || |
5 ++|+H+-- +++ ++
|+N+ - ---+H+------+H+------ |
+ +N+--+H++----+H+---+--+H+----++H+--- + + +H+---+--+H|
0 ++---------+----------+---------+----------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 5000000 ops/thread, [0,8] range

40 ++---------+----------+---------+----------+----------+----------+---++
++atomic +-E--+ + + + + + |
35 +cmpxchg +-H--+ ++
| master +-N--+ ---+E+------+E+------+E+-----+E+------+E|
30 ++| ---+E+-- +++ ++
| | -+E+--- |
25 ++E ---- +++ ++
|+++++ -+E+ |
20 +E+ E-- +++ ++
|H|+++ |
|+| +H+------- |
15 ++H+ ---+++ +H+------ ++
|N++H+-- +++--- +H+------++|
10 ++ +++ - +++ ---+H+ +++ +H+
| | +H+-----+H+------+H+-- |
5 ++| +++ ++
++N+N+--+N++ + + + + + |
0 ++---------+----------+---------+----------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 5000000 ops/thread, [0,128] range

160 ++---------+---------+----------+---------+----------+----------+---++
+ atomic +-E--+ + + + + + |
140 +cmpxchg +-H--+ +++ +++ ++
| master +-N--+ E--------E------+E+------++|
120 ++ --| | +++ E+
| -- +++ +++ ++|
100 ++ - ++
| +++- +++ ++|
80 ++ -+E+ -+H+------+H+------H--------++
| ---- ---- +++ H|
| ---+E+-----+E+- ---+H+ ++|
60 ++ +E+--- +++ ---+H+--- ++
| --+++ ---+H+-- |
40 ++ +E+-+H+--- ++
| +H+ |
20 +EE+ ++
+N+ + + + + + + |
0 ++N-N---N--+---------+----------+---------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 5000000 ops/thread, [0,1024] range

350 ++---------+---------+----------+---------+----------+----------+---++
+ atomic +-E--+ + + + + + |
300 +cmpxchg +-H--+ +++
| master +-N--+ +++ ||
| +++ | ----E|
250 ++ | ----E---- ++
| ----E--- | ---+H|
200 ++ -+E+--- +++ ---+H+--- ++
| ---- -+H+-- |
| +E+ +++ ---- +++ |
150 ++ ---+++ ---+H+- ++
| --- -+H+-- |
100 ++ ---+E+ ---- +++ ++
| +++ ---+E+-----+H+- |
| -+E+------+H+-- |
50 ++ +E+ ++
+EE+ + + + + + + |
0 ++N-N---N--+---------+----------+---------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

hi-res: http://imgur.com/a/fMRmq

For master I stopped measuring master after 8 threads, because there is little
point in measuring the well-known performance collapse of a contended lock.

Backports commit 37b995f6e7a1cb6fa378c5cd4217b9dd9e1fc98b from qemu

qemu/target-i386/helper.h

@@ -3,8 +3,6 @@ DEF_HELPER_4(uc_tracecode, void, i32, i32, ptr, i64)
 DEF_HELPER_FLAGS_4(cc_compute_all, TCG_CALL_NO_RWG_SE, tl, tl, tl, tl, int)
 DEF_HELPER_FLAGS_4(cc_compute_c, TCG_CALL_NO_RWG_SE, tl, tl, tl, tl, int)
 
-DEF_HELPER_1(lock, void, env)
-DEF_HELPER_1(unlock, void, env)
 DEF_HELPER_3(write_eflags, void, env, tl, i32)
 DEF_HELPER_1(read_eflags, tl, env)
 DEF_HELPER_2(divb_AL, void, env, tl)

qemu/target-i386/mem_helper.c

@@ -27,16 +27,6 @@
 
 #include "uc_priv.h"
 
-/* broken thread support */
-
-void helper_lock(CPUX86State *env)
-{
-}
-
-void helper_unlock(CPUX86State *env)
-{
-}
-
 void helper_cmpxchg8b_unlocked(CPUX86State *env, target_ulong a0)
 {
     uintptr_t ra = GETPC();

qemu/target-i386/translate.c

@@ -5184,10 +5184,6 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
     s->aflag = aflag;
     s->dflag = dflag;
 
-    /* lock generation */
-    if (prefixes & PREFIX_LOCK)
-        gen_helper_lock(tcg_ctx, cpu_env);
-
     /* now check op code */
  reswitch:
     switch(b) {
@@ -8947,9 +8943,6 @@ case 0x101:
     default:
         goto unknown_op;
     }
-    /* lock generation */
-    if (s->prefix & PREFIX_LOCK)
-        gen_helper_unlock(tcg_ctx, cpu_env);
 
     // Unicorn: patch the callback for the instruction size
     if (HOOK_EXISTS_BOUNDED(env->uc, UC_HOOK_CODE, pc_start)) {
@@ -8975,15 +8968,9 @@ case 0x101:
 
     return s->pc;
  illegal_op:
-    if (s->prefix & PREFIX_LOCK)
-        gen_helper_unlock(tcg_ctx, cpu_env);
-    /* XXX: ensure that no lock was generated */
     gen_illegal_opcode(s);
     return s->pc;
  unknown_op:
-    if (s->prefix & PREFIX_LOCK)
-        gen_helper_unlock(tcg_ctx, cpu_env);
-    /* XXX: ensure that no lock was generated */
     gen_unknown_opcode(env, s);
     return s->pc;
 }