Speedup lnp_state_machine::handle_special_opcode
Commit Message
On 13-02-2020 14:03, Richard Biener wrote:
> Care to pick up this one-time patch without myself becoming familiar
> with gdb testing & patch submission?
Of course. Added ChangeLog entry, build and reg-tested on x86_64-linux.
Thanks,
- Tom
Comments
Arguably the the compiler should do this for us. *cough* :-)
On 2/13/20 2:23 PM, Tom de Vries wrote:
> On 13-02-2020 14:03, Richard Biener wrote:
>> Care to pick up this one-time patch without myself becoming familiar
>> with gdb testing & patch submission?
>
> Of course. Added ChangeLog entry, build and reg-tested on x86_64-linux.
The ChangeLog entry (as well a git author) should reflect the patch's
authorship.
Otherwise OK.
Thanks,
Pedro Alves
On 13-02-2020 19:26, Pedro Alves wrote:
> Arguably the the compiler should do this for us. *cough* :-)
>
> On 2/13/20 2:23 PM, Tom de Vries wrote:
>> On 13-02-2020 14:03, Richard Biener wrote:
>>> Care to pick up this one-time patch without myself becoming familiar
>>> with gdb testing & patch submission?
>>
>> Of course. Added ChangeLog entry, build and reg-tested on x86_64-linux.
>
> The ChangeLog entry (as well a git author) should reflect the patch's
> authorship.
>
Committed with those change @
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=258bf0ee3748d4354e13daf00f02266cafa96389
.
Thanks,
- Tom
[gdb] Speedup lnp_state_machine::handle_special_opcode
I see for some program at gdb startup:
...
Samples: 102K of event 'cycles:pu', Event count (approx.): 91710925103
Overhead Command Shared Object Symbol
15.21% gdb gdb [.]
lnp_state_machine::handle_special
...
where the divisions are the places we stall. The following
micro-optimizes things but it smells like m_line_header->line_range
is constant, likewise probably m_line_header->maximum_ops_per_instruction
so eventually the divisions could be avoided completely with some
lookup table.
Well. Micro-optimizing with this patch improves things
(don't expect [load] CSE over the gdbarch_adjust_dwarf2_line call).
Build and reg-tested on x86_64-linux.
gdb/ChangeLog:
2020-02-13 Tom de Vries <tdevries@suse.de>
* dwarf2/read.c (lnp_state_machine::handle_special_opcode): Apply CSE
on expression with division operators.
---
gdb/dwarf2/read.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
@@ -19812,16 +19812,16 @@ void
lnp_state_machine::handle_special_opcode (unsigned char op_code)
{
unsigned char adj_opcode = op_code - m_line_header->opcode_base;
- CORE_ADDR addr_adj = (((m_op_index
- + (adj_opcode / m_line_header->line_range))
+ unsigned char adj_opcode_d = adj_opcode / m_line_header->line_range;
+ unsigned char adj_opcode_r = adj_opcode % m_line_header->line_range;
+ CORE_ADDR addr_adj = (((m_op_index + adj_opcode_d)
/ m_line_header->maximum_ops_per_instruction)
* m_line_header->minimum_instruction_length);
m_address += gdbarch_adjust_dwarf2_line (m_gdbarch, addr_adj, true);
- m_op_index = ((m_op_index + (adj_opcode / m_line_header->line_range))
+ m_op_index = ((m_op_index + adj_opcode_d)
% m_line_header->maximum_ops_per_instruction);
- int line_delta = (m_line_header->line_base
- + (adj_opcode % m_line_header->line_range));
+ int line_delta = m_line_header->line_base + adj_opcode_r;
advance_line (line_delta);
record_line (false);
m_discriminator = 0;