Re: [Qemu-devel] [PATCH v5 1/9] tcg: pass down TranslationBlock to tcg_code_gen

[Richard Henderson <rth@twiddle.net>]

On 02/05/2016 01:56 AM, Alex Bennée wrote:
> diff --git a/translate-all.c b/translate-all.c
> index ab61fac..dce00d5 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -1055,7 +1055,6 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>       TranslationBlock *tb;
>       tb_page_addr_t phys_pc, phys_page2;
>       target_ulong virt_page2;
> -    tcg_insn_unit *gen_code_buf;
>       int gen_code_size, search_size;
>   #ifdef CONFIG_PROFILER
>       int64_t ti;
> @@ -1078,8 +1077,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>           tcg_ctx.tb_ctx.tb_invalidated_flag = 1;
>       }
>
> -    gen_code_buf = tcg_ctx.code_gen_ptr;
> -    tb->tc_ptr = gen_code_buf;
> +    tb->tc_ptr = tcg_ctx.code_gen_ptr;

Why get rid of the gen_code_buf variable?  You're forcing the compiler to keep 
reloading the value from memory.

Certainly that's not relevant to passing down TB to tcg_gen_code, and is a 
separate change that ought to be separately defended.


r~

>       tb->cs_base = cs_base;
>       tb->flags = flags;
>       tb->cflags = cflags;
> @@ -1119,11 +1117,11 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>          the tcg optimization currently hidden inside tcg_gen_code.  All
>          that should be required is to flush the TBs, allocate a new TB,
>          re-initialize it per above, and re-do the actual code generation.  */
> -    gen_code_size = tcg_gen_code(&tcg_ctx, gen_code_buf);
> +    gen_code_size = tcg_gen_code(&tcg_ctx, tb);
>       if (unlikely(gen_code_size < 0)) {
>           goto buffer_overflow;
>       }
> -    search_size = encode_search(tb, (void *)gen_code_buf + gen_code_size);
> +    search_size = encode_search(tb, (void *)tb->tc_ptr + gen_code_size);
>       if (unlikely(search_size < 0)) {
>           goto buffer_overflow;
>       }
> @@ -1145,7 +1143,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>   #endif
>
>       tcg_ctx.code_gen_ptr = (void *)
> -        ROUND_UP((uintptr_t)gen_code_buf + gen_code_size + search_size,
> +        ROUND_UP((uintptr_t)tb->tc_ptr + gen_code_size + search_size,
>                    CODE_GEN_ALIGN);
>
>       /* check next page if needed */
>