Re: [Qemu-devel] [PATCH 2/5] tcg: reorganize tb_find_physical loop

[Paolo Bonzini <pbonzini@redhat.com>]

On 29/03/2016 15:19, Sergey Fedorov wrote:
> On 22/03/16 17:59, Alex Bennée wrote:
>> sergey.fedorov@linaro.org writes:
>>
>>> From: Paolo Bonzini <pbonzini@redhat.com>
>>>
>>> Use a continue statement.
>>>
>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>> [Sergey Fedorov: Fix moving to list head in case of no TB]
>>> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
>>> ---
>>>  cpu-exec.c | 50 +++++++++++++++++++++++++-------------------------
>>>  1 file changed, 25 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/cpu-exec.c b/cpu-exec.c
>>> index fd92452f16f6..f90482eff778 100644
>>> --- a/cpu-exec.c
>>> +++ b/cpu-exec.c
>>> @@ -225,37 +225,37 @@ static TranslationBlock *tb_find_physical(CPUState *cpu,
>>>      phys_pc = get_page_addr_code(env, pc);
>>>      phys_page1 = phys_pc & TARGET_PAGE_MASK;
>>>      h = tb_phys_hash_func(phys_pc);
>>> -    ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>>> -    for(;;) {
>>> -        tb = *ptb1;
>>> -        if (!tb) {
>>> -            return NULL;
>>> +    for (ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>>> +         (tb = *ptb1) != NULL;
>>> +         ptb1 = &tb->phys_hash_next) {
>> I'm not sure I'm keen on the assignment in the for condition clause. I
>> appreciate the cleansing of the if !tb return exit though. Could we be
>> cleaner maybe? Here is my attempt:
>>
>>     static TranslationBlock *tb_find_physical(CPUState *cpu,
>>                                               target_ulong pc,
>>                                               target_ulong cs_base,
>>                                               uint64_t flags)
>>     {
>>         CPUArchState *env = (CPUArchState *)cpu->env_ptr;
>>         TranslationBlock *tb, **tb_hash_head, **ptb1;
>>         unsigned int h;
>>         tb_page_addr_t phys_pc, phys_page1;
>>
>>         /* find translated block using physical mappings */
>>         phys_pc = get_page_addr_code(env, pc);
>>         phys_page1 = phys_pc & TARGET_PAGE_MASK;
>>         h = tb_phys_hash_func(phys_pc);
>>
>>         /* Start at head of the hash entry */
>>         ptb1 = tb_hash_head = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>>         tb = *ptb1;
>>
>>         while (tb) {
>>
>>             if (tb->pc == pc &&
>>                 tb->page_addr[0] == phys_page1 &&
>>                 tb->cs_base == cs_base &&
>>                 tb->flags == flags) {
>>
>>                 if (tb->page_addr[1] == -1) {
>>                     /* done, we have a match */
>>                     break;
>>                 } else {
>>                     /* check next page if needed */
>>                     target_ulong virt_page2 = (pc & TARGET_PAGE_MASK)
>>                         + TARGET_PAGE_SIZE;
>>                     tb_page_addr_t phys_page2 = get_page_addr_code(env, virt_page2);
>>
>>                     if (tb->page_addr[1] == phys_page2) {
>>                         break;
>>                     }
>>                 }
>>             }
>>
>>             ptb1 = &tb->phys_hash_next;
>>             tb = *ptb1;
>>         }
>>
>>         if (tb) {
>>             /* Move the TB to the head of the list */
>>             *ptb1 = tb->phys_hash_next;
>>             tb->phys_hash_next = *tb_hash_head;
>>             *tb_hash_head = tb;
>>         }
>>         return tb;
>>     }
>>
>> FWIW the compiled code is 9 bytes shorter on my machine.
> 
> Looks like another attempt to rewrite it. I am wondering whom to
> attribute as an author, then? :)

I don't really care. :)

Paolo