[all-commits] [llvm/llvm-project] cb46e8: [JITLink][RISCV] Avoid quadratic removal of alignm...

[Thrrreeee via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cb46e8530f3c45be6f968fcdef47f37e5220fe95
      https://github.com/llvm/llvm-project/commit/cb46e8530f3c45be6f968fcdef47f37e5220fe95
  Author: Thrrreeee <shijinrui at bytedance.com>
  Date:   2026-09-10 (Thu, 10 Sep 2026)

  Changed paths:
    M llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
    A llvm/test/ExecutionEngine/JITLink/RISCV/ELF_relax_many_align.s

  Log Message:
  -----------
  [JITLink][RISCV] Avoid quadratic removal of alignment edges (#222317)

We encountered this issue while using BOLT to instrument clang on
RISC-V. JITLink spent significant time removing alignment edges during
relaxation finalization in large code blocks with many alignment
relocations.

During RISC-V relaxation finalization, finalizeBlockRelax removes
AlignRelaxable edges individually from a block's edge vector. Each erase
shifts the remaining suffix, making this cleanup quadratic when the
number of alignment edges grows with the total edge count.

Compact surviving edges once and remove the trailing entries from the
back, preserving edge order and making cleanup linear. Count the
trailing entries before erasing to avoid comparing an invalidated
iterator.


These results support the performance benefit, but they come from
**GPT-generated** synthetic benchmarks and do not represent speedups on
real BOLT workloads.

count |  origin | new
-- | -- | --
16,384 | 92.6 ms | 6.2 ms
32,768 | 430.0 ms | 9.5 ms
65,536 | 1,732.3 ms | 16.2 ms

Assisted by GPT-6.



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