riscv_dis_opts_cache_support

Disassembler: Cache instruction class support

• Status: Waiting for a prerequisite to be Merged
• Branch: riscv-dis-opts-cache-support
• Tracking PR: #22 (view Pull Request and Diff)
• Mailing List:
  • Not yet

Requires

• Disassembler: Minor optimizations (batch 1)
  • Requires: Disassembler: Use faster hash table

Feature Description

As I mentioned in the previous patchset, calling riscv_subset_supports repeatedly harms the performance in a measurable way (about 3-13% in total).

As a simple solution, this patch now caches instruction class support as a signed char array.

Performance Improvements

On disassembling linked RISC-V ELF files using objdump, performance improvements achieved by this patchset is about 4-8%. Not bad for a simple change.

This is relative to the previous optimization.

objdump (near regular cases)

Program	Improvements
Busybox 1.35.1 (RV64GC)	6.3-6.9%
OpenSBI 1.1 (generic fw_*.elf)	5.8-7.4%
Linux kernel 5.18 (vmlinux)	6.0-7.5%
Linux kernel 5.18 (vmlinux.o)	(-1.5)-2.4%
glibc (libc.so.6)	6.3-6.9%
glibc (libc.a)	(-0.8)-(-0.4)%
newlib (libc.a)	(-0.6)-1.2%

objdump (special cases)

Program	Improvements
Random files (/dev/urandom)	7.4-7.9%
1M (1048576) CSR instructions	34.8%

gdb: near all code region of disas

Program	Improvements
Linux kernel 5.18 (vmlinux) with debug info	0.8%
Linux kernel 5.18 (vmlinux) without debug info	1.3%
OpenSBI 1.1 (generic fw_*.elf)	0.4-5.8%