On Wed, Jul 12, 2017 at 7:08 PM, Richard Henderson <r...@twiddle.net> wrote:
> On 07/12/2017 12:14 PM, Pranith Kumar wrote:
>>
>> Use ADR instruction for shorter jumps.
>>
>> I was going through rth's email and realized that I should have done
>> this the first time.
>>
>> Signed-off-by: Pranith Kumar <bobby.pr...@gmail.com>
>> ---
>> tcg/aarch64/tcg-target.inc.c | 14 +++++++++-----
>> 1 file changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
>> index 04bc369a92..5121ebc1a1 100644
>> --- a/tcg/aarch64/tcg-target.inc.c
>> +++ b/tcg/aarch64/tcg-target.inc.c
>> @@ -886,12 +886,16 @@ void aarch64_tb_set_jmp_target(uintptr_t jmp_addr,
>> uintptr_t addr)
>> i1 = I3206_B | ((offset >> 2) & 0x3ffffff);
>> i2 = NOP;
>> } else {
>> - offset = (addr >> 12) - (jmp_addr >> 12);
>> + if (offset == sextract64(offset, 0, 21)) {
>> + i1 = I3406_ADR;
>> + i2 = NOP;
>> + } else {
>
>
> This is dead code because it is covered by the direct jump above.
> B has a 26-bit range, whereas ADR has a 21-bit range.
Hmm, yep. And I guess it doesn't make sense to use ADR for short jumps
because this will be a 2 instruction jump vs 1 instruction for direct
branch.
Thanks,
--
Pranith
