From 258bf0ee3748d4354e13daf00f02266cafa96389 Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Fri, 14 Feb 2020 08:32:53 +0100 Subject: [PATCH] [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 * dwarf2/read.c (lnp_state_machine::handle_special_opcode): Apply CSE on expression with division operators. --- gdb/ChangeLog | 5 +++++ gdb/dwarf2/read.c | 10 +++++----- 2 files changed, 10 insertions(+), 5 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index eb3c0a836e1..a79aabcbeed 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2020-02-14 Richard Biener + + * dwarf2/read.c (lnp_state_machine::handle_special_opcode): Apply CSE + on expression with division operators. + 2020-02-13 Alok Kumar Sharma * MAINTAINERS (Write After Approval): Adding myself. diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 7edbd9d7dfa..e74383e01dc 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -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; -- 2.30.2