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.
+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.
2020-02-13 Alok Kumar Sharma <AlokKumar.Sharma@amd.com>
* MAINTAINERS (Write After Approval): Adding myself.
lnp_state_machine::handle_special_opcode (unsigned char op_code)
{
unsigned char adj_opcode = op_code - m_line_header->opcode_base;
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_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);
% 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;
advance_line (line_delta);
record_line (false);
m_discriminator = 0;