Just a little precursor re-factoring before I was going to add a trace
point:

  - single return point, defaulting to tcg_ctx.code_gen_epilogue
  - move cs_base, pc and flags inside the jump cache hit scope
  - calculate the tb_jmp_cache hash once

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 tcg-runtime.c | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/tcg-runtime.c b/tcg-runtime.c
index 7fa90ce508..f4bfa9cea6 100644
--- a/tcg-runtime.c
+++ b/tcg-runtime.c
@@ -147,30 +147,33 @@ uint64_t HELPER(ctpop_i64)(uint64_t arg)
 void *HELPER(lookup_tb_ptr)(CPUArchState *env, target_ulong addr)
 {
     CPUState *cpu = ENV_GET_CPU(env);
+    unsigned int addr_hash = tb_jmp_cache_hash_func(addr);
+    void *code_ptr = NULL;
     TranslationBlock *tb;
-    target_ulong cs_base, pc;
-    uint32_t flags;
 
-    tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)]);
+    tb = atomic_rcu_read(&cpu->tb_jmp_cache[addr_hash]);
     if (likely(tb)) {
+        target_ulong cs_base, pc;
+        uint32_t flags;
+
         cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
+
         if (likely(tb->pc == addr && tb->cs_base == cs_base &&
                    tb->flags == flags)) {
-            goto found;
-        }
-        tb = tb_htable_lookup(cpu, addr, cs_base, flags);
-        if (likely(tb)) {
-            atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)], tb);
-            goto found;
+            code_ptr = tb->tc_ptr;
+        } else {
+            /* If we didn't find it in the jmp_cache we still might
+             * find it in the global tb_htable
+             */
+            tb = tb_htable_lookup(cpu, addr, cs_base, flags);
+            if (likely(tb)) {
+                atomic_set(&cpu->tb_jmp_cache[addr_hash], tb);
+                code_ptr = tb->tc_ptr;
+            }
         }
     }
-    return tcg_ctx.code_gen_epilogue;
- found:
-    qemu_log_mask_and_addr(CPU_LOG_EXEC, addr,
-                           "Chain %p [%d: " TARGET_FMT_lx "] %s\n",
-                           tb->tc_ptr, cpu->cpu_index, addr,
-                           lookup_symbol(addr));
-    return tb->tc_ptr;
+
+    return code_ptr ? code_ptr : tcg_ctx.code_gen_epilogue;
 }
 
 void HELPER(exit_atomic)(CPUArchState *env)
-- 
2.13.0

On 06/14/2017 07:02 AM, Alex Bennée wrote:
> Just a little precursor re-factoring before I was going to add a trace
> point:
> 
>    - single return point, defaulting to tcg_ctx.code_gen_epilogue

Why?  Any if you're going to do that, why not init ret = epilogue and avoid the 
null test at the end?

>    - move cs_base, pc and flags inside the jump cache hit scope

Funny story.  While looking at this again, I notice that there's no reason to 
avoid, and every reason not to avoid, calling tb_htable_lookup when 
tb_jmp_cache is empty.  So I'm now doing

     tb = atomic_rcu_read(...);
     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);

     if (!(tb && tb->pc == addr && ...)) {
         tb = tb_htable_lookup(...);
         ...

>    - calculate the tb_jmp_cache hash once

I did look once and the compiler is doing the CSE.  But it does look cleaner.


r~

Richard Henderson <rth@twiddle.net> writes:

> On 06/14/2017 07:02 AM, Alex Bennée wrote:
>> Just a little precursor re-factoring before I was going to add a trace
>> point:
>>
>>    - single return point, defaulting to tcg_ctx.code_gen_epilogue
>
> Why?  Any if you're going to do that, why not init ret = epilogue and
> avoid the null test at the end?

That would be better. I think the NULL is left over from my originall
debugging when I had added a trace point and wanted to see when the
lookup had failed.

>
>>    - move cs_base, pc and flags inside the jump cache hit scope
>
> Funny story.  While looking at this again, I notice that there's no
> reason to avoid, and every reason not to avoid, calling
> tb_htable_lookup when tb_jmp_cache is empty.  So I'm now doing
>
>     tb = atomic_rcu_read(...);
>     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
>
>     if (!(tb && tb->pc == addr && ...)) {
>         tb = tb_htable_lookup(...);
>         ...

OK I can fix on the next iteration.

>>    - calculate the tb_jmp_cache hash once
>
> I did look once and the compiler is doing the CSE.  But it does look cleaner.
>
>
> r~


--
Alex Bennée