[Bug gas/26406] New: Extreme assembling time regression with 2.35 and master

[franz.sirl at lauterbach dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=26406

            Bug ID: 26406
           Summary: Extreme assembling time regression with 2.35 and
                    master
           Product: binutils
           Version: 2.35
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: franz.sirl at lauterbach dot com
  Target Milestone: ---

Hi,

I just stumbled over an extreme slowdown in assembler performance. On a 265
MByte .s file (gcc10 assembly output of a 27000 line C source compiled with -O2
-fno-inline + debug + ASAN + UBSAN) the assembler of 2.34 takes ~49-59sec, but
the 2.35 assembler takes ~65-74min. Both use about 3.6 GBytes of memory. That's
quite a performance regression.

fsirl@ds1:~> time as-2.35 --64 -o sample.o sample.s

real    74m11.921s
user    73m45.203s
sys     0m13.132s
fsirl@ds1:~> time as-2.34 --64 -o sample.o sample.s

real    0m49.454s
user    0m46.331s
sys     0m2.623s

Most of the time seems to be spent in _bfd_elf_write_secondary_reloc_section().

The slowdown started with this commit:

commit a8e14f4cc2badfcf959f5e2cc57a941dc43f72d4
Author: Nick Clifton <nickc@redhat.com>
Date:   Thu Mar 5 15:47:15 2020 +0000

    Add support for ELF files which contain multiple reloc sections which all
target the same section.

Unfortunately I cannot share the testcase, but I can do any requested
debugging/testing.

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