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[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:

2020-02-14  Richard Biener  <rguenther@suse.de>

	* dwarf2/read.c (lnp_state_machine::handle_special_opcode): Apply CSE
	on expression with division operators.
This commit is contained in:
Richard Biener 2020-02-14 08:32:53 +01:00 committed by Tom de Vries
parent d4059b1d6c
commit 258bf0ee37
2 changed files with 10 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
gdb/ChangeLog
View File

@ -1,3 +1,8 @@
2020-02-14 Richard Biener <rguenther@suse.de>
* dwarf2/read.c (lnp_state_machine::handle_special_opcode): Apply CSE
on expression with division operators.
2020-02-13 Alok Kumar Sharma <AlokKumar.Sharma@amd.com>
* MAINTAINERS (Write After Approval): Adding myself.

10
gdb/dwarf2/read.c
View File

@ -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;